U.S. patent number RE42,627 [Application Number 11/726,762] was granted by the patent office on 2011-08-16 for encoding and decoding of information in audio signals.
This patent grant is currently assigned to Arbitron, Inc.. Invention is credited to James M. Jensen, Wendell D. Lynch, Alan R. Neuhauser.
United States Patent |
RE42,627 |
Neuhauser , et al. |
August 16, 2011 |
Encoding and decoding of information in audio signals
Abstract
Systems and methods are provided for decoding a message symbol
in an audio signal. This message symbol is represented by first and
second code symbols displaced in time. Values representing the code
signals are accumulated and the accumulated values are examined to
detect the message symbol.
Inventors: |
Neuhauser; Alan R. (Silver
Spring, MD), Lynch; Wendell D. (East Lansing, MI),
Jensen; James M. (Shelton, WA) |
Assignee: |
Arbitron, Inc. (Columbia,
MD)
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Family
ID: |
23236391 |
Appl.
No.: |
11/726,762 |
Filed: |
March 22, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
09318045 |
May 25, 1999 |
6871180 |
Mar 22, 2005 |
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Current U.S.
Class: |
704/500; 725/18;
725/14; 380/205 |
Current CPC
Class: |
G10L
19/018 (20130101); H04H 20/31 (20130101); H04H
2201/50 (20130101) |
Current International
Class: |
H04Q
11/04 (20060101); H04L 27/26 (20060101); H04L
1/08 (20060101); H04N 9/00 (20060101) |
Field of
Search: |
;704/200,200.1,201,205,206,270,273,501,502,503,504
;380/201,202,205,3,4,6 ;375/355,362,365,366,132 ;348/1 ;725/14,18
;370/511 |
References Cited
[Referenced By]
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S. Macera (representing Kiefl) re: alleged patent infringement.
cited by other.
|
Primary Examiner: Lerner; Martin
Attorney, Agent or Firm: Barnes & Thornburg LLP
Claims
What is claimed is:
1. A system for decoding a predetermined message symbol of a
plurality of message symbols embedded in an audio signal,
comprising: means for receiving an audio signal in which a
plurality of message symbols have been incorporated so that the
message symbols are inaudible when the audio signal is reproduced
audibly, the plurality of message symbols being contained within a
predetermined message as a plurality of code symbols, the
predetermined message symbol being represented by first and second
code symbols incorporated in and displaced in time in the audio
signal with at least one code symbol representing a different one
of the message symbols being incorporated in the audio signal and
positioned in time between the first and second code symbols; means
for accumulating a first signal value of the first code symbol
representing the predetermined message symbol and a second signal
value of the second code symbol representing the predetermined
message symbol; and means for examining the accumulated first and
second signal values to detect the predetermined message symbol
represented by the first and second code symbols.
2. The system of claim 1, wherein the accumulating means is
operative to produce a third signal value derived from the first
and second signal values and the examining means is operative to
detect the predetermined message symbol based on the third signal
value.
3. The system of claim 2, wherein the accumulating means is
operative to produce the third signal value by linearly combining
the first and second signal values.
4. The system of claim 2, wherein the accumulating means is
operative to produce the third signal value as a non-linear
function of the first and second signal values.
5. The system of claim 1, wherein the accumulating means is
operative to store the first and second signal values, and the
examining means is operative to detect the predetermined message
symbol by examining both of the first and second signal values.
6. The system of claim 1, wherein the receiving means comprises an
acoustic transducer for transducing an acoustic audio signal to an
electrical signal, the acoustic audio signal having a plurality of
code symbols representing a plurality of message symbols comprising
source data for the acoustic audio signal, and further comprising a
memory for storing indications of detected message symbols.
7. The system of claim 5, further comprising a housing for the
system adapted to be carried on the person of an audience member
and means for transmitting the stored data for use in producing
audience estimates.
8. A method for decoding a predetermined message symbol of a
plurality of message symbols incorporated in an audio signal,
comprising: receiving an audio signal in which a plurality of
message symbols have been incorporated so that the message symbols
are inaudible when the audio signal is reproduced audibly, the
plurality of message symbols being contained within a predetermined
message as a plurality of code symbols, the predetermined message
symbol being represented by first and second code symbols
incorporated in and displaced in time in the audio signal with at
least one code symbol representing a different one of the message
symbols being incorporated in the audio signal and positioned in
time between the first and second code symbols; accumulating a
first signal value of the first code symbol representing the
predetermined message symbol and a second signal value of the
second code symbol representing the predetermined message symbol;
and examining the accumulated first and second signal values to
detect the predetermined message symbol.
9. The method of claim 8, further comprising receiving the first
and second code symbols by transducing an acoustic audio signal to
an electrical signal, the acoustic audio signal having a plurality
of message symbols comprising source data for the acoustic audio
signal, and storing data representing indications of detected
message symbols.
10. The method of claim 9, further comprising transmitting the
stored data for use in producing audience estimates.
11. A system for decoding a predetermined message symbol of a
plurality of message symbols incorporated in an audio signal,
comprising: an input device for an audio signal in which a
plurality of message symbols have been incorporated so that the
message symbols are inaudible when the audio signal is reproduced
audibly, the plurality of message symbols being contained within a
predetermined message as a plurality of code symbols, the
predetermined message symbol being represented by first and second
code symbols incorporated in and displaced in time in the audio
signal with at least one code symbol representing a different one
of the message symbols being incorporated in the audio signal and
positioned in time between the first and second code symbols; and a
digital processor in communication with the input device to receive
the audio signal therefrom, the digital processor being programmed
to accumulate a first signal value representing the first code
symbol and a second signal value representing the second code
symbol, the digital processor being further programmed to examine
the accumulated first and second signal values to detect the
predetermined message symbol.
12. The system of claim 11, wherein the input device comprises an
acoustic transducer for transducing an acoustic signal to an
electrical signal, the acoustic audio signal having a plurality of
code symbols representing a plurality of message symbols comprising
source data for the acoustic audio signal, the digital processor
having a memory for storing data representing indications of
detected message symbols.
13. The system of claim 12, further comprising a housing for the
system adapted to be carried on the person of an audience member
and means for transmitting the stored data for use in producing
audience estimates.
14. A system for decoding a predetermined message symbol of a
plurality of message symbols embedded in an audio signal,
comprising: means for receiving an audio signal in which a
plurality of message symbols have been incorporated so that the
message symbols are inaudible when the audio signal is reproduced
audibly, the plurality of message symbols being contained within a
predetermined message as a plurality of code symbols, the
predetermined message symbol being represented by first and second
code symbols incorporated in and displaced in time in the audio
signal with at least one code symbol representing a different one
of the message symbols being incorporated in the audio signal and
positioned in time between the first and second code symbols, the
first and second code symbols each comprising a predetermined
number of frequency components; means for producing first and
second sets of component values, each set corresponding to a
respective one of the first and second code symbols and each
component value of each set representing a characteristic of a
respective frequency component of the corresponding symbol; means
for accumulating a first signal value of the first code symbol
representing the predetermined message symbol based on the first
set of component values and a second signal value of the second
code symbol representing the predetermined message symbol based on
the second set of component values; and means for examining the
accumulated first and second signal values to detect the
predetermined message symbol represented by the first and second
code symbols.
15. A method for decoding a predetermined message symbol of a
plurality of message symbols incorporated in an audio signal,
comprising: receiving an audio signal in which a plurality of
message symbols have been incorporated so that the message symbols
are inaudible when the audio signal is reproduced audibly, the
plurality of message symbols being contained within a predetermined
message as a plurality of code symbols, the predetermined message
symbol being represented by first and second code symbols
incorporated in and displaced in time in the audio signal with at
least one code symbol representing a different one of the message
symbols being incorporated in the audio signal and positioned in
time between the first and second code symbols, the first and
second code symbols each comprising a predetermined number of
frequency components; producing first and second sets of component
values, each set corresponding to a respective one of the first and
second code symbols and each component value of each set
representing a characteristic of a respective frequency component
of the corresponding symbol; accumulating a first signal value of
the first code symbol representing the predetermined message symbol
based on the first set of component values and a second signal
value of the second code symbol representing the predetermined
message symbol based on the second set of component values; and
examining the accumulated first and second signal values to detect
the predetermined message symbol.
16. A system for decoding a predetermined message symbol of a
plurality of message symbols incorporated in an audio signal,
comprising: an input device for an audio signal in which a
plurality of message symbols have been incorporated so that the
message symbols are inaudible when the audio signal is reproduced
audibly, the plurality of message symbols being contained within a
predetermined message as a plurality of code symbols, the
predetermined message symbol being represented by first and second
code symbols incorporated in and displaced in time in the audio
signal with at least one code symbol representing a different one
of the message symbols being incorporated in the audio signal and
positioned in time between the first and second code symbols, the
first and second code symbols each comprising a predetermined
number of frequency components; and a digital processor in
communication with the input device to receive the audio signal
therefrom, the digital processor being programmed to produce first
and second sets of component values, each set corresponding to a
respective one of the first and second code symbols and each
component value of each set representing a characteristic of a
respective frequency component of the corresponding symbol the
digital processor being further programmed to produce a first
signal value based on the first set of component values and a
second signal value based on the second set of component values and
to accumulate a first signal value representing the first code
symbol and a second signal value representing the second code
symbol, the digital processor being further programmed to examine
the accumulated first and second signal values to detect the
predetermined message symbol.
17. A system for decoding predetermined message symbols of a
plurality of message symbols embedded in an audio signal,
comprising: means for receiving an audio signal in which a
plurality of message symbols have been incorporated so that the
message symbols are inaudible when the audio signal is reproduced
audibly, the plurality of message symbols being represented by
plural sets of first and second code symbols, each set representing
a respective one of the plurality of message symbols, the plural
sets of first and second code symbols being arranged as a message
having a predetermined sequence including at least one marker
symbol and at least one data symbol, at least one of the marker
symbol and the data symbol being represented by first and second
code symbols incorporated in and displaced in time in the audio
signal with at least one code symbol representing a different one
of the message symbols being incorporated in the audio signal and
positioned in time between the first and second code symbols; means
for accumulating sets of first and second signal values, each
signal value set corresponding to a respective one of the sets of
first and second code symbols and including a first signal value
representing the first code symbol of the respective code symbol
set and a second signal value representing the second code symbol
thereof; and means for examining the accumulated sets of first and
second signal values to detect the presence of the at least one
marker symbol based on its signal value set and to detect the at
least one data symbol based on the detected presence of the at
least one marker symbol and the corresponding signal value set of
the at least one data symbol.
18. A method for decoding predetermined message symbols of a
plurality of message symbols incorporated in an audio signal,
comprising: receiving an audio signal in which a plurality of
message symbols have been incorporated so that the message symbols
are inaudible when the audio signal is reproduced audibly, the
plurality of message symbols being represented by plural sets of
first and second code symbols, each set representing a respective
one of the plurality of message symbols, the plural sets of first
and second code symbols being arranged as a message having a
predetermined sequence including at least one marker symbol and at
least one data symbol, at least one of the marker symbol and the
data symbol being represented by first and second code symbols
incorporated in and displaced in time in the audio signal with at
least one code symbol representing a different one of the message
symbols being incorporated in the audio signal and positioned in
time between the first and second code symbols; accumulating sets
of first and second signal values, each signal value set
corresponding to a respective one of the sets of first and second
code symbols and including a first signal value representing the
first code symbol of the respective code symbol set and a second
signal value representing the second code symbol thereof; and
examining the accumulated sets of first and second signal values to
detect the presence of the marker symbol based on its signal value
set and to detect at least one data symbol based on the detected
presence of the marker symbol and the corresponding signal value
set of the at least one data symbol.
19. A system for decoding predetermined message symbols of a
plurality of message symbols incorporated in an audio signal,
comprising: an input device for an audio signal in which a
plurality of message symbols have been incorporated so that the
message symbols are inaudible when the audio signal is reproduced
audibly, the plurality of message symbols being represented by
plural sets of first and second code symbols, each set representing
a respective one of the plurality of message symbols, the plural
sets of first and second code symbols being arranged as a message
having a predetermined sequence including at least one marker
symbol and at least one data symbol, at least one of the marker
symbol and the data symbol being represented by first and second
code symbols incorporated in and displaced in time in the audio
signal with at least one code symbol representing a different one
of the message symbols being incorporated in the audio signal and
positioned in time between the first and second code symbols; and a
digital processor in communication with the input device to receive
the audio signal therefrom, the digital processor being programmed
to accumulate sets of first and second signal values, each signal
value set corresponding to a respective one of the sets of first
and second code symbols and including a first signal value
representing the first code symbol of the respective code symbol
set and a second signal value representing the second code symbol
thereof, the digital processor being further programmed to examine
the accumulated sets of first and second signal values to detect
the presence of the marker symbol based on its signal value set and
to detect at least one data symbol based on the detected presence
of the marker symbol and the corresponding signal value set of the
at least one data symbol.
20. A system for decoding a predetermined message symbol of a
plurality of message symbols embedded in an audio signal,
comprising: means for receiving an audio signal in which a
plurality of message symbols have been incorporated so that the
message symbols are inaudible when the audio signal is reproduced
audibly, the plurality of message symbols being contained within a
predetermined message as a plurality of code symbols, the
predetermined message symbol being represented by first and second
code symbols incorporated in and displaced in time in the audio
signal with at least one code symbol representing a different one
of the message symbols being incorporated in the audio signal and
positioned in time between the first and second code symbols; means
for accumulating a first signal value of the first code symbol
representing the predetermined message symbol and a second signal
value of the second code symbol representing the predetermined
message symbol, wherein the accumulating means is operative to
produce the first and second signal values based on multiple other
signal values; and means for examining the accumulated first and
second signal values to detect the predetermined message symbol
represented by the first and second code symbols.
21. A method for decoding a predetermined message symbol of a
plurality of message symbols incorporated in an audio signal,
comprising: receiving an audio signal in which a plurality of
message symbols have been incorporated so that the message symbols
are inaudible when the audio signal is reproduced audibly, the
plurality of message symbols being contained within a predetermined
message as a plurality of code symbols, the predetermined message
symbol being represented by first and second code symbols
incorporated in and displaced in time in the audio signal with at
least one code symbol representing a different one of the message
symbols being incorporated in the audio signal and positioned in
time between the first and second code symbols; accumulating a
first signal value of the first code symbol representing the
predetermined message symbol and a second signal value of the
second code symbol representing the predetermined message symbol
based on multiple other signal values; and examining the
accumulated first and second signal values to detect the
predetermined message symbol.
22. A system for decoding a predetermined message symbol of a
plurality of message symbols incorporated in an audio signal,
comprising: an input device for an audio signal in which a
plurality of message symbols have been incorporated so that the
message symbols are inaudible when the audio signal is reproduced
audibly, the plurality of message symbols being contained within a
predetermined message as a plurality of code symbols, the
predetermined message symbol being represented by first and second
code symbols incorporated in and displaced in time in the audio
signal with at least one code symbol representing a different one
of the message symbols being incorporated in the audio sign al and
positioned in time between the first and second code symbols; and a
digital processor in communication with the input device to receive
the audio signal therefrom, the digital processor being programmed
to accumulate a first signal value representing the first code
symbol and a second signal value representing the second code
symbol based on multiple other signal values, the digital processor
being further programmed to examine the accumulated first and
second signal values to detect the predetermined message
symbol.
23. A system for decoding a predetermined message symbol of a
plurality of message symbols embedded in an audio signal,
comprising: means for receiving an audio signal in which a
plurality of message symbols have been incorporated so that the
message symbols are inaudible when the audio signal is reproduced
audibly, the plurality of message symbols being contained within a
predetermined message as a plurality of code symbols, the
predetermined message symbol being represented by first and second
code symbols incorporated in and displaced in time in the audio
signal with at least one code symbol representing a different one
of the message symbols being incorporated in the audio signal and
positioned in time between the first and second code symbols; means
for accumulating a first signal value of the first code symbol
representing the predetermined message symbol and a second signal
value of the second code symbol representing the predetermined
message symbol, wherein the first and second signal values are
produced from respective sets of time displaced signal values, each
of the time displaced signal values representing a value of a
respective one of the first and second code symbols during a
corresponding time period thereof; and means for examining the
accumulated first and second signal values to detect the
predetermined message symbol represented by the first and second
code symbols.
24. A method for decoding a predetermined message symbol of a
plurality of message symbols incorporated in an audio signal,
comprising: receiving an audio signal in which a plurality of
message symbols have been incorporated so that the message symbols
are inaudible when the audio signal is reproduced audibly, the
plurality of message symbols being contained within a predetermined
message as a plurality of code symbols, the predetermined message
symbol being represented by first and second code symbols
incorporated in and displaced in time in the audio signal with at
least one code symbol representing a different one of the message
symbols being incorporated in the audio signal and positioned in
time between the first and second code symbols; accumulating a
first signal value of the first code symbol representing the
predetermined message symbol and a second signal value of the
second code symbol representing the predetermined message symbol,
wherein the first and second signal values are produced from
respective sets of time displaced signal values, each of the time
displaced signal values representing a value of a respective one of
the first and second code symbols during a corresponding time
period thereof; and examining the accumulated first and second
signal values to detect the predetermined message symbol.
25. A system for decoding a predetermined message symbol of a
plurality of message symbols incorporated in an audio signal,
comprising: an input device for an audio signal in which a
plurality of message symbols have been incorporated so that the
message symbols are inaudible when the audio signal is reproduced
audibly, the plurality of message symbols being contained within a
predetermined message as a plurality of code symbols, the
predetermined message symbol being represented by first and second
code symbols incorporated in and displaced in time in the audio
signal with at least one code symbol representing a different one
of the message symbols being incorporated in the audio signal and
positioned in time between the first and second code symbols; and a
digital processor in communication with the input device to receive
the audio signal therefrom, the digital processor being programmed
to accumulate a first signal value representing the first code
symbol and a second signal value representing the second code
symbol, wherein the first and second signal values are produced
from respective sets of time displaced signal values, each of the
time displaced signal values representing a value of a respective
one of the first and second code symbols during a corresponding
time period thereof, the digital processor being further programmed
to examine the accumulated first and second signal values to detect
the predetermined message symbol.
26. A system for decoding a predetermined message symbol of a
plurality of message symbols embedded in an audio signal,
comprising: means for receiving an audio signal in which a
plurality of message symbols have been incorporated so that the
message symbols are inaudible when the audio signal is reproduced
audibly, the plurality of message symbols being contained within a
predetermined message as a plurality of code symbols, the
predetermined message symbol being represented by first and second
code symbols incorporated in and displaced in time in the audio
signal with at least one code symbol representing a different one
of the message symbols being incorporated in the audio signal and
positioned in time between the first and second code symbols, the
first and second code symbols each comprising a predetermined
number of frequency components; means for producing first and
second sets of component values, each set corresponding to a
respective one of the first and second code symbols and each
component value of each set representing a characteristic of a
respective frequency component of the corresponding symbol; means
for accumulating a first signal value of the first code symbol
representing the predetermined message symbol based on the first
set of component values and a second signal value of the second
code symbol representing the predetermined message symbol based on
the second set of component values, and for producing a third
signal value derived from the first and second signal values; and
means for detecting the predetermined message symbol represented by
the first and second code symbols based on the third signal
value.
27. A system for decoding a message represented by a plurality of
message symbols embedded in an audio signal, comprising: means for
receiving an audio signal in which a plurality of message symbols
have been incorporated so that the message symbols are inaudible
when the audio signal is reproduced audibly, the plurality of
message symbols being represented by plural sets of first and
second code symbols, each set representing a respective one of the
plurality of message symbols, the plural sets of first and second
code symbols being arranged as a message having a predetermined
sequence including at least one marker symbol and at least one data
symbol, at least one of the marker symbol and the data symbol being
represented by first and second code symbols incorporated in and
displaced in time in the audio signal with at least one code symbol
representing a different one of the message symbols being
incorporated in the audio signal and positioned in time between the
first and second code symbols; means for accumulating sets of first
and second signal values, each signal value set corresponding to a
respective one of the sets of first and second code symbols and
including a first signal value representing the first code symbol
of the respective code symbol set and a second signal value
representing the second code symbol thereof and for producing a
third signal value derived from the first and second signal values;
and means for detecting a respective one of the plurality of
message symbols represented by the first and second code symbols
based on the third signal value and for detecting the message by
detecting the presence of the marker symbol based on its signal
value set and detecting at least one data symbol based on the
detected presence of the marker symbol and the corresponding signal
value set of the at least one data symbol.
28. A system for decoding a predetermined message symbol of a
plurality of message symbols embedded in an audio signal,
comprising: means for receiving an audio signal in which a
plurality of message symbols have been incorporated so that the
message symbols are inaudible when the audio signal is reproduced
audibly, the plurality of message symbols being contained within a
predetermined message as a plurality of code symbols, the
predetermined message symbol being represented by first and second
code symbols incorporated in and displaced in time in the audio
signal with at least one code symbol representing a different one
of the message symbols being incorporated in the audio signal and
positioned in time between the first and second code symbols; means
for accumulating a first signal value of the first code symbol
representing the predetermined message symbol and a second signal
value of the second code symbol representing the predetermined
message symbol, wherein the accumulating means is operative to
produce the first and second signal values based on multiple other
signal values and wherein the accumulating means is operative to
store the first and second signal values; and means for examining
both of the accumulated first and second signal values to detect
the predetermined message symbol represented by the first and
second code symbols.
29. The system of claim 28, wherein the first and second signal
values are produced from respective sets of time displaced signal
values, each of the time displaced signal values representing a
value of a respective one of the first and second code symbols
during a corresponding time period thereof.
30. The system of claim 28, wherein the first and second code
symbols each comprise a predetermined number of frequency
components, and further comprising means for producing first and
second sets of component values, each set corresponding to a
respective one of the first and second code symbols and each
component value of each set representing a characteristic of a
respective frequency component of the corresponding symbol, and
means for producing the first signal value based on the first set
of component values and producing the second signal value based on
the second set of component values.
31. A method for decoding a predetermined message symbol of a
plurality of message symbols embedded in an audio signal,
comprising: receiving an audio signal in which a plurality of
message symbols have been incorporated so that the message symbols
are inaudible when the audio signal is reproduced audibly, the
plurality of message symbols being contained within a predetermined
message as a plurality of code symbols, the predetermined message
symbol being represented by first and second code symbols
incorporated in and displaced in time in the audio signal with at
least one code symbol representing a different one of the message
symbols being incorporated in the audio signal and positioned in
time between the first and second code symbols, the first and
second code symbols each comprising a predetermined number of
frequency components; producing first and second sets of component
values, each set corresponding to a respective one of the first and
second code symbols and each component value of each set
representing a characteristic of a respective frequency component
of the corresponding symbol; accumulating a first signal value of
the first code symbol representing the predetermined message symbol
based on the first set of component values and a second signal
value of the second code symbol representing the predetermined
message symbol based on the second set of component values, and for
producing a third signal value derived from the first and second
signal values; and detecting the predetermined message symbol
represented by the first and second code symbols based on the third
signal value.
32. A method for decoding a message represented by a plurality of
message symbols embedded in an audio signal, comprising: receiving
an audio signal in which a plurality of message symbols have been
incorporated so that the message symbols are inaudible when the
audio signal is reproduced audibly, the plurality of message
symbols being represented by plural sets of first and second code
symbols, each set representing a respective one of the plurality of
message symbols, the plural sets of first and second code symbols
being arranged as a message having a predetermined sequence
including at least one marker symbol and at least one data symbol,
at least one of the marker symbol and the data symbol being
represented by first and second code symbols incorporated in and
displaced in time in the audio signal with at least one code symbol
representing a different one of the message symbols being
incorporated in the audio signal and positioned in time between the
first and second code symbols; accumulating sets of first and
second signal values, each signal value set corresponding to a
respective one of the sets of first and second code symbols and
including a first signal value representing the first code symbol
of the respective code symbol set and a second signal value
representing the second code symbol thereof; producing a third
signal value derived from the first and second signal values;
detecting a respective one of the plurality of message symbols
represented by the first and second code symbols based on the third
signal value; and detecting the message by detecting the presence
of the marker symbol based on its signal value set and detecting at
least one data symbol based on the detected presence of the marker
symbol and the corresponding signal value set of the at least one
data symbol.
33. A method for decoding a predetermined message symbol of a
plurality of message symbols embedded in an audio signal,
comprising: receiving an audio signal in which a plurality of
message symbols have been incorporated so that the message symbols
are inaudible when the audio signal is reproduced audibly, the
plurality of message symbols being contained within a predetermined
message as a plurality of code symbols, the predetermined message
symbol being represented by first and second code symbols
incorporated in and displaced in time in the audio signal with at
least one code symbol representing a different one of the message
symbols being incorporated in the audio signal and positioned in
time between the first and second code symbols; accumulating a
first signal value of the first code symbol representing the
predetermined message symbol and a second signal value of the
second code symbol representing the predetermined message symbol
based on multiple other signal values; storing the first and second
signal values; and examining both of the accumulated first and
second signal values to detect the predetermined message symbol
represented by the first and second code symbols.
34. The method of claim 33, wherein the first and second signal
values are produced from respective sets of time displaced signal
values, each of the time displaced signal values representing a
value of a respective one of the first and second code symbols
during a corresponding time period thereof.
35. The method of claim 33, wherein the first and second code
symbols each comprise a predetermined number of frequency
components, and further comprising producing first and second sets
of component values, each set corresponding to a respective one of
the first and second code symbols and each component value of each
set representing a characteristic of a respective frequency
component of the corresponding symbol, and producing the first
signal value based on the first set of component values and
producing the second signal value based on the second set of
component values.
36. A system for decoding a predetermined message symbol of a
plurality of message symbols embedded in an audio signal,
comprising: an input device for an audio signal in which a
plurality of message symbols have been incorporated so that the
message symbols are inaudible when the audio signal is reproduced
audibly, the plurality of message symbols being contained within a
predetermined message as a plurality of code symbols, the
predetermined message symbol being represented by first and second
code symbols incorporated in and displaced in time in the audio
signal with at least one code symbol representing a different one
of the message symbols being incorporated in the audio signal and
positioned in time between the first and second code symbols, the
first and second code symbols each comprising a predetermined
number of frequency components; a digital processor in
communication with the input device to receive the audio signal
therefrom, the digital processor being programmed to produce first
and second sets of component values, each set corresponding to a
respective one of the first and second code symbols and each
component value of each set representing a characteristic of a
respective frequency component of the corresponding symbol, the
digital processor being further programmed to accumulate a first
signal value of the first code symbol representing the
predetermined message symbol based on the first set of component
values and a second signal value of the second code symbol
representing the predetermined message symbol based on the second
set of component values, to produce a third signal value derived
from the first and second signal values, and to detect the
predetermined message symbol represented by the first and second
code symbols based on the third signal value.
37. A system for decoding a message represented by a plurality of
message symbols embedded in an audio signal, comprising: an input
device for an audio signal in which a plurality of message symbols
have been incorporated so that the message symbols are inaudible
when the audio signal is reproduced audibly, the plurality of
message symbols being represented by plural sets of first and
second code symbols, each set representing a respective one of the
plurality of message symbols, the plural sets of first and second
code symbols being arranged as a message having a predetermined
sequence including at least one marker symbol and at least one data
symbol, at least one of the marker symbol and the data symbol being
represented by first and second code symbols incorporated in and
displaced in time in the audio signal with at least one code symbol
representing a different one of the message symbols being
incorporated in the audio signal and positioned in time between the
first and second code symbols; and a digital processor in
communication with the input device to receive the audio signal
therefrom, the digital processor being programmed to accumulate
sets of first and second signal values, each signal value set
corresponding to a respective one of the sets of first and second
code symbols and including a first signal value representing the
first code symbol of the respective code symbol set and a second
signal value representing the second code symbol thereof, the
digital processor being further programmed to produce a third
signal value derived from the first and second signal values, to
detect a respective one of the plurality of message symbols
represented by the first and second code symbols based on the third
signal value, and to detect the message by detecting the presence
of the marker symbol based on its signal value set and detecting at
least one data symbol based on the detected presence of the marker
symbol and the corresponding signal value set of the at least one
data symbol.
38. A system for decoding a predetermined message symbol of a
plurality of message symbols embedded in an audio signal,
comprising: an input device for an audio signal in which a
plurality of message symbols have been incorporated so that the
message symbols are inaudible when the audio signal is reproduced
audibly, the plurality of message symbols being contained within a
predetermined message as a plurality of code symbols, the
predetermined message symbol being represented by first and second
code symbols incorporated in and displaced in time in the audio
signal with at least one code symbol representing a different one
of the message symbols being incorporated in the audio signal and
positioned in time between the first and second code symbols; and a
digital processor in communication with the input device to receive
the audio signal therefrom, the digital processor being programmed
to accumulate a first signal value of the first code symbol
representing the predetermined message symbol and a second signal
value of the second code symbol representing the predetermined
message symbol based on multiple other signal values, to store the
first and second signal values, and to examine both of the
accumulated first and second signal values to detect the
predetermined message symbol represented by the first and second
code symbols.
39. The system of claim 38, wherein the first and second signal
values are produced from respective sets of time displaced signal
values, each of the time displaced signal values representing a
value of a respective one of the first and second code symbols
during a corresponding time period thereof.
40. The system of claim 38, wherein the first and second code
symbols each comprise a predetermined number of frequency
components, and wherein the digital processor is programmed to
produce first and second sets of component values, each set
corresponding to a respective one of the first and second code
symbols and each component value of each set representing a
characteristic of a respective frequency component of the
corresponding symbol, and the digital processor is further
programmed to produce the first signal value based on the first set
of component values and to produce the second signal value based on
the second set of component values.
.Iadd.41. A method of encoding a predetermined message in an audio
signal using a processing device, comprising: encoding the audio
signal using the processing device with a first encoded sequence of
code symbols representing the predetermined message; and encoding
the audio signal using the processing device with a second encoded
sequence of code symbols representing the predetermined message,
such that the second encoded sequence of code symbols differs from
the first encoded sequence of code symbols and the second encoded
sequence of code symbols is displaced in time in the audio signal
with respect to the first encoded sequence of code symbols; wherein
each of the code symbols in the first encoded sequence of code
symbols comprises a first plurality of single frequency components
and each of the code symbols in the second encoded sequence of code
symbols comprises a second plurality of single frequency
components, and wherein the first encoded sequence of code symbols
has a frequency content which differs at least in part from a
frequency content of the second encoded sequence of code
symbols..Iaddend.
.Iadd.42. A method according to claim 41, wherein each code symbol
in the first encoded sequence of code symbols corresponds to a
respective code symbol in the second encoded sequence of code
symbols, and wherein each code symbol in the first encoded sequence
of code symbols has a frequency content which differs at least in
part from a frequency content of the respective code symbol in the
second encoded sequence of code symbols..Iaddend.
.Iadd.43. A method according to claim 41, wherein the code symbols
in the first and second encoded sequences of code symbols are
selected from a predetermined set of code symbols in which the code
symbols are arranged in a predetermined order, and wherein each
code symbol of the second encoded sequence of code symbols
corresponds to a respective code symbol of the first encoded
sequence of code symbols and is selected based on the order of the
respective code symbol of the first encoded sequence of code
symbols..Iaddend.
.Iadd.44. A method according to claim 43, wherein each code symbol
of the second encoded sequence of code symbols is selected from the
predetermined set of code symbols based on a predetermined offset
in the predetermined order from the respective code symbol of the
first encoded sequence of code symbols..Iaddend.
.Iadd.45. A method according to claim 44, wherein the predetermined
offset is the same for all code symbols of the second encoded
sequence of code symbols..Iaddend.
.Iadd.46. A method according to claim 41, wherein the code symbols
of the first and second encoded sequences of code symbols are
selected from a predetermined set of code symbols and wherein each
code symbol in the predetermined set of code symbols comprises a
combination of single-frequency code components unique among all
combinations of single frequency code components of the code
symbols within the predetermined set of code symbols..Iaddend.
.Iadd.47. A method according to claim 41, wherein the processing
device is a record device storing a recorded audio signal encoded
with a predetermined message..Iaddend.
.Iadd.48. A method according to claim 47, wherein each code symbol
in the first encoded sequence of code symbols corresponds to a
respective code symbol in the second encoded sequence of code
symbols..Iaddend.
.Iadd.49. A method according to claim 47, wherein the code symbols
in the first and second encoded sequences of code symbols are
selected from a predetermined set of code symbols in which the code
symbols are arranged in a predetermined order, and wherein each
code symbol of the second encoded sequence of code symbols
corresponds to a respective code symbol of the first encoded
sequence of code symbols and is selected based on the order of the
respective code symbol of the first encoded sequence of code
symbols..Iaddend.
.Iadd.50. A method according to claim 49, wherein each code symbol
of the second encoded sequence of code symbols is selected from the
predetermined set of code symbols based on a predetermined offset
in the predetermined order from the respective code symbol of the
first encoded sequence of code symbols..Iaddend.
.Iadd.51. A method according to claim 50, wherein the predetermined
offset is the same for all code symbols of the second encoded
sequence of code symbols..Iaddend.
.Iadd.52. A method according to claim 47, wherein the code symbols
of the first and second encoded sequences of code symbols are
selected from a predetermined set of code symbols and wherein each
code symbol in the predetermined set of code symbols comprises a
combination of single-frequency code components unique among all
combinations of single frequency code components of the code
symbols within the predetermined set of code symbols..Iaddend.
.Iadd.53. A method for encoding information in an audio signal
using a processing device, comprising the steps of: translating an
information signal using the processing device into a first set of
code symbols representing the information signal and a second set
of code symbols representing the information signal, such that each
of the code symbols in the first and second sets of code symbols
comprises a corresponding plurality of single-frequency code
components, at least some of the single-frequency code components
of the code symbols in the first set of code symbols differing from
the single-frequency code components of the code symbols in the
second set of code symbols; and, using the processing device,
combining the single-frequency code components of the first and
second sets of code symbols with the audio signal to produce an
encoded audio signal, such that the single-frequency code
components of the code symbols in the first set of code symbols are
time-displaced from the single-frequency code components of the
code symbols in the second set of code symbols in the audio
signal..Iaddend.
.Iadd.54. A method according to claim 53, wherein the processing
device is a record device storing a recorded audio signal encoded
with a predetermined message..Iaddend.
.Iadd.55. A method of encoding a predetermined message in an audio
signal using a processing device, comprising: encoding the audio
signal using the processing device with a first encoded sequence of
code symbols representing the predetermined message; and encoding
the audio signal with a second encoded sequence of code symbols
representing the predetermined message, such that the second
encoded sequence of code symbols differs from the first encoded
sequence of code symbols and the second encoded sequence of code
symbols is displaced in time in the audio signal with respect to
the first encoded sequence of code symbols; wherein the first
encoded sequence of code symbols has a frequency content which
differs at least in part from a frequency content of the second
encoded sequence of code symbols..Iaddend.
.Iadd.56. A method according to claim 55, wherein each code symbol
in the first encoded sequence of code symbols corresponds to a
respective code symbol in the second encoded sequence of code
symbols, and wherein each code symbol in the first encoded sequence
of code symbols has a frequency content which differs at least in
part from a frequency content of its respective code symbol in the
second encoded sequence of code symbols..Iaddend.
.Iadd.57. A method according to claim 55, wherein the code symbols
in the first and second encoded sequences of code symbols are
selected from a predetermined set of code symbols in which the code
symbols are arranged in a predetermined order, and wherein each
code symbol of the second encoded sequence of code symbols
corresponds to a respective code symbol of the first encoded
sequence of code symbols and is selected based on the order of the
respective code symbol of the first encoded sequence of code
symbols..Iaddend.
.Iadd.58. A method according to claim 57, wherein each code symbol
of the second encoded sequence of code symbols is selected from the
predetermined set of code symbols based on a predetermined offset
in the predetermined order from the respective code symbol of the
first encoded sequence of code symbols..Iaddend.
.Iadd.59. A method according to claim 58, wherein the predetermined
offset is the same for all code symbols of the second encoded
sequence of code symbols..Iaddend.
.Iadd.60. A method according to claim 55, wherein the code symbols
of the first and second encoded sequences of code symbols are
selected from a predetermined set of code symbols and wherein each
code symbol in the predetermined set of code symbols comprises a
combination of single-frequency code components unique among all
combinations of single frequency code components of the code
symbols within the predetermined set of code signals..Iaddend.
.Iadd.61. A method according to claim 55, wherein the processing
device is a record device storing a recorded audio signal encoded
with a predetermined message..Iaddend.
.Iadd.62. A method according to claim 61, wherein each code symbol
in the first encoded sequence of code symbols corresponds to a
respective code symbol in the second encoded sequence of code
symbols, and wherein each code symbol in the first encoded sequence
of code symbols has a frequency content which differs at least in
part from a frequency content of the respective code symbol in the
second encoded sequence of code symbols..Iaddend.
.Iadd.63. A method according to claim 61, wherein the code symbols
of the first and second encoded sequences of code symbols are
selected from a predetermined set of code symbols and wherein each
code symbol in the predetermined set of code symbols comprises a
combination of single-frequency code components unique among all
combinations of single frequency code components of the code
symbols within the predetermined set of code symbols..Iaddend.
.Iadd.64. A method according to claim 61, wherein the code symbols
in the first and second encoded sequences of code symbols are
selected from a predetermined set of code symbols in which the code
symbols are arranged in a predetermined order, and wherein each
code symbol of the second encoded sequence of code symbols
corresponds to a respective code symbol of the first encoded
sequence of code symbols and is selected based on the order of the
respective code symbol of the first encoded sequence of code
symbols..Iaddend.
.Iadd.65. A method according to claim 64, wherein each code symbol
of the second encoded sequence of code symbols is selected from the
predetermined set of code symbols based on a predetermined offset
in the predetermined order from the respective code symbol of the
first encoded sequence of code symbols..Iaddend.
.Iadd.66. A method according to claim 65, wherein the predetermined
offset is the same for all code symbols of the second encoded
sequence of code symbols..Iaddend.
.Iadd.67. A method of encoding a predetermined message in an audio
signal using a processing device, comprising: encoding the audio
signal using the processing device with a first encoded sequence of
code symbols representing the predetermined message; and encoding
the audio signal using the processing device with a second encoded
sequence of code symbols representing the predetermined message,
such that the second encoded sequence of code symbols differs from
the first encoded sequence of code symbols and the second encoded
sequence of code symbols is displaced in time in the audio signal
with respect to the first encoded sequence of code symbols; wherein
each code symbol in the second encoded sequence of code symbols
corresponds to a respective code symbol in the first encoded
sequence of code symbols, and wherein each code symbol in the
second encoded sequence of code symbols has a frequency content
which differs at least in part from a frequency content of the
corresponding code symbol in the first encoded sequence of code
symbols..Iaddend.
.Iadd.68. A method according to claim 67, wherein the code symbols
in the first and second encoded sequences of code symbols are
selected from a predetermined set of code symbols in which the code
symbols are arranged in a predetermined order, and wherein each
code symbol of the second encoded sequence of code symbols is
selected based on the predetermined order of the corresponding code
symbol of the first encoded sequence of code symbols..Iaddend.
.Iadd.69. A method according to claim 68, wherein each code symbol
of the second encoded sequence of code symbols is selected from the
predetermined set of code symbols based on a predetermined offset
in the predetermined order from the corresponding code symbol of
the first encoded sequence of code symbols..Iaddend.
.Iadd.70. A method according to claim 69, wherein the predetermined
offset is the same for all code symbols of the second encoded
sequence of code symbols..Iaddend.
.Iadd.71. A method according to claim 67, wherein the processing
device is a record device storing a recorded audio signal encoded
with a predetermined message..Iaddend.
.Iadd.72. A method according to claim 71, wherein the code symbols
in the first and second encoded sequences of code symbols are
selected from a predetermined set of code symbols in which the code
symbols are arranged in a predetermined order, and wherein each
code symbol of the second encoded sequence of code symbols is
selected based on the predetermined order of the corresponding code
symbol of the first encoded sequence of code symbols..Iaddend.
.Iadd.73. A method according to claim 72, wherein each code symbol
of the second encoded sequence of code symbols is selected from the
predetermined set of code symbols based on a predetermined offset
in the predetermined order from the corresponding code symbol of
the first encoded sequence of code symbols..Iaddend.
.Iadd.74. A method according to claim 73, wherein the predetermined
offset is the same for all code symbols of the second encoded
sequence of code symbols..Iaddend.
.Iadd.75. A method of encoding a predetermined message in an audio
signal using a processing device, comprising: encoding the audio
signal using the processing device with a first encoded sequence of
code symbols representing the predetermined message; and encoding
the audio signal using the processing device with a second encoded
sequence of code symbols representing the predetermined message,
such that the second encoded sequence of code symbols differs from
the first encoded sequence of code symbols and the second encoded
sequence of code symbols is displaced in time in the audio signal
with respect to the first encoded sequence of code symbols, wherein
the first and second encoded sequences of code symbols are
inaudible when the audio signal is reproduced audibly; wherein the
code symbols of the first and second encoded sequences of code
symbols are selected from a predetermined set of code symbols in
which the code symbols are arranged in a predetermined order, and
wherein each code symbol of the second encoded sequence of code
symbols corresponds to a respective code symbol of the first
encoded sequence of code symbols and is selected based on the order
of the respective code symbol of the first encoded sequence of code
symbols, and wherein the first encoded sequence of code symbols has
a frequency content which differs at least in part from a frequency
content of the second encoded sequence of code
symbols..Iaddend.
.Iadd.76. A method according to claim 75, wherein each code symbol
of the second encoded sequence of code symbols is selected from the
predetermined set of code symbols based on a predetermined offset
in the predetermined order from its respective code symbol of the
first encoded sequence of code symbols..Iaddend.
.Iadd.77. A method according to claim 76, wherein the predetermined
offset is the same for all code symbols of the second encoded
sequence of code symbols..Iaddend.
.Iadd.78. A method according to claim 75, wherein the processing
device comprises a record device storing a recorded audio signal
encoded with a predetermined message..Iaddend.
.Iadd.79. A method according to claim 78, wherein each code symbol
of the second encoded sequence of code symbols is selected from the
predetermined set of code symbols based on a predetermined offset
in the predetermined order from the respective code symbol of the
first encoded sequence of code symbols..Iaddend.
.Iadd.80. A method according to claim 79, wherein the predetermined
offset is the same for all code symbols of the second encoded
sequence of code symbols..Iaddend.
.Iadd.81. A method of encoding a predetermined message in an audio
signal using a processing device, comprising: encoding the audio
signal using the processing device with a first encoded sequence of
code symbols representing the predetermined message; encoding the
audio signal using the processing device with a second encoded
sequence of code symbols representing the predetermined message,
such that the second encoded sequence of code symbols differs from
the first encoded sequence of code symbols and the second encoded
sequence of code symbols is displaced in time in the audio signal
with respect to the first encoded sequence of code symbols; and
wherein the code symbols of the first and second encoded sequences
of code symbols are selected from a predetermined set of code
symbols and each code symbol of the predetermined set of code
symbols comprises a combination of single-frequency code components
unique among all combinations of single-frequency code components
of the code symbols within the predetermined set of code symbols,
and wherein the first encoded sequence of code symbols has a
frequency content which differs at least in part from a frequency
content of the second encoded sequence of code
symbols..Iaddend.
.Iadd.82. A method according to claim 81, wherein the processing
device comprises a record device storing a recorded audio signal
encoded with a predetermined message..Iaddend.
.Iadd.83. A method of encoding a predetermined message in an audio
signal in a processing device, comprising: encoding the audio
signal using the processing device with a first encoded sequence of
code symbols representing the predetermined message, each of the
first encoded code symbols comprising a first plurality of single
frequency components; and encoding the audio signal using the
processing device with a second encoded sequence of code symbols
representing the predetermined message, each of the second encoded
code symbols comprising a second plurality of single frequency
components, such that the second encoded sequence of code symbols
differs from the first encoded sequence of code symbols and the
second encoded sequence of code symbols is displaced in time in the
audio signal with respect to the first encoded sequence of code
symbols, and wherein the first encoded sequence of code symbols has
a frequency content which differs at least in part from a frequency
content of the second encoded sequence of code
symbols..Iaddend.
.Iadd.84. A method according to claim 83, further comprising:
encoding the audio signal with a marker symbol positioned in time
adjacent at least one of the first encoded sequence of code symbols
and the second encoded sequence of code symbols..Iaddend.
.Iadd.85. A method according to claim 83, further comprising:
encoding the audio signal with a first marker symbol adjacent the
first encoded sequence of code symbols and a second marker symbol
adjacent the second encoded sequence of code symbols..Iaddend.
.Iadd.86. A method according to claim 83, wherein the processing
device comprises a record device storing a recorded audio signal
encoded with a predetermined message..Iaddend.
.Iadd.87. A method according to claim 86, further comprising:
encoding the audio signal with a marker symbol positioned in time
adjacent at least one of the first encoded sequence of code symbols
and the second encoded sequence of code symbols..Iaddend.
.Iadd.88. A method according to claim 86, further comprising:
encoding the audio signal with a marker symbol adjacent the first
encoded sequence of code symbols and adjacent the second encoded
sequence of code symbols..Iaddend.
.Iadd.89. An apparatus for encoding a predetermined message in an
audio signal, comprising: a memory an encoder, operatively coupled
to the memory, that encodes the audio signal with a first encoded
sequence of code symbols representing the predetermined message and
a second encoded sequence of code symbols representing the
predetermined message, such that the second encoded sequence of
code symbols differs from the first encoded sequence of code
symbols and the second encoded sequence of code symbols is
displaced in time in the audio signal with respect to the first
encoded sequence of code symbols; wherein each of the code symbols
in the first encoded sequence of code symbols comprises a first
plurality of single frequency components and each of the code
symbols in the second encoded sequence of code symbols comprises a
second plurality of single frequency components, and wherein the
first encoded sequence of code symbols has a frequency content
which differs at least in part from a frequency content of the
second encoded sequence of code symbols..Iaddend.
.Iadd.90. An apparatus according to claim 89, wherein each code
symbol in the first encoded sequence of code symbols corresponds to
a respective code symbol in the second encoded sequence of code
symbols..Iaddend.
.Iadd.91. An apparatus according to claim 89, wherein the code
symbols in the first and second encoded sequences of code symbols
are selected from a predetermined set of code symbols in which the
code symbols are arranged in a predetermined order, and wherein
each code symbol of the second encoded sequence of code symbols
corresponds to a respective code symbol of the first encoded
sequence of code symbols and is selected based on the order of the
respective code symbol of the first encoded sequence of code
symbols..Iaddend.
.Iadd.92. An apparatus according to claim 91, wherein each code
symbol of the second encoded sequence of code symbols is selected
from the predetermined set of code symbols based on a predetermined
offset in the predetermined order from the respective code symbol
of the first encoded sequence of code symbols..Iaddend.
.Iadd.93. An apparatus according to claim 92, wherein the
predetermined offset is the same for all code symbols of the second
encoded sequence of code symbols..Iaddend.
.Iadd.94. An apparatus according to claim 89, wherein the code
symbols of the first and second encoded sequences of code symbols
are selected from a predetermined set of code symbols and wherein
each code symbol in the predetermined set of code symbols comprises
a combination of single-frequency code components unique among all
combinations of single frequency code components of the code
symbols within the predetermined set of code symbols..Iaddend.
.Iadd.95. An apparatus for encoding information in an audio signal,
comprising: a translator that translates an information signal into
a first set of code symbols representing the information signal and
a second set of code symbols representing the information signal,
each of the code symbols in the first and second sets of code
symbols having a corresponding plurality of single-frequency code
components, such that at least some of the single-frequency code
components of the code symbols in the first set of code symbols
differ from the single-frequency code components of code symbols in
the second set of code symbols; and an encoder that combines the
single-frequency code components of the first and second sets of
code symbols with the audio signal to produce an encoded audio
signal, such that the single-frequency code components of the code
symbols in the first set of code symbols are time-displaced from
the single-frequency code components of the code symbols in the
second set of code symbols in the audio signal..Iaddend.
.Iadd.96. An apparatus for encoding a predetermined message in an
audio signal, comprising: a memory; an encoder, operatively coupled
to the memory, that encodes the audio signal with a first encoded
sequence of code symbols representing the predetermined message and
a second encoded sequence of code symbols representing the
predetermined message, such that the second encoded sequence of
code symbols differs from the first encoded sequence of code
symbols and the second encoded sequence of code symbols is
displaced in time in the audio signal with respect to the first
encoded sequence of code symbols; and wherein the first encoded
sequence of code symbols has a frequency content which differs at
least in part from a frequency content of the second encoded
sequence of code symbols..Iaddend.
.Iadd.97. An apparatus according to claim 96, wherein each code
symbol in the first encoded sequence of code symbols corresponds to
a respective code symbol in the second encoded sequence of code
symbols, and wherein each code symbol in the first encoded sequence
of code symbols has a frequency content which differs at least in
part from a frequency content of the respective code symbol in the
second encoded sequence of code symbols..Iaddend.
.Iadd.98. An apparatus according to claim 96, wherein the code
symbols in the first and second encoded sequences of code symbols
are selected from a predetermined set of code symbols in which the
code symbols are arranged in a predetermined order, and wherein
each code symbol of the second encoded sequence of code symbols
corresponds to a respective code symbol of the first encoded
sequence of code symbols and is selected based on the order of the
respective code symbol of the first encoded sequence of code
symbols..Iaddend.
.Iadd.99. An apparatus according to claim 98, wherein each code
symbol of the second encoded sequence of code symbols is selected
from the predetermined set of code symbols based on a predetermined
offset in the predetermined order from the respective code symbol
of the first encoded sequence of code symbols..Iaddend.
.Iadd.100. An apparatus according to claim 99, wherein the
predetermined offset is the same for all code symbols of the second
encoded sequence of code symbols..Iaddend.
.Iadd.101. An apparatus according to claim 96, wherein the code
symbols of the first and second encoded sequences of code symbols
are selected from a predetermined set of code symbols and wherein
each code symbol in the predetermined set of code symbols comprises
a combination of single-frequency code components unique among all
combinations of single frequency code components of the code
symbols within the predetermined set of code symbols..Iaddend.
.Iadd.102. An apparatus for encoding a predetermined message in an
audio signal, comprising: a memory; an encoder, operatively coupled
to the memory, that encodes the audio signal with a first encoded
sequence of code symbols representing the predetermined message and
a second encoded sequence of code symbols representing the
predetermined message, such that the second encoded sequence of
code symbols differs from the first encoded sequence of code
symbols and the second encoded sequence of code symbols is
displaced in time in the audio signal with respect to the first
encoded sequence of code symbols; and wherein each code symbol in
the second encoded sequence of code symbols corresponds to a
respective code symbol in the first encoded sequence of code
symbols, and wherein each code symbol in the second encoded
sequence of code symbols has a frequency content which differs at
least in part from a frequency content of the corresponding code
symbol in the first encoded sequence of code symbols..Iaddend.
.Iadd.103. An apparatus according to claim 102, wherein the code
symbols in the first and second encoded sequences of code symbols
are selected from a predetermined set of code symbols in which the
code symbols are arranged in a predetermined order, and wherein
each code symbol of the second encoded sequence of code symbols is
selected based on the predetermined order of the corresponding code
symbol of the first encoded sequence of code symbols..Iaddend.
.Iadd.104. An apparatus according to claim 103, wherein each code
symbol of the second encoded sequence of code symbols is selected
from the predetermined set of code symbols based on a predetermined
offset in the predetermined order from the corresponding code
symbol of the first encoded sequence of code symbols..Iaddend.
.Iadd.105. An apparatus according to claim 104, wherein the
predetermined offset is the same for all code symbols of the second
encoded sequence of code symbols..Iaddend.
.Iadd.106. An apparatus for encoding a predetermined message in an
audio signal, comprising: a memory; and an encoder, operatively
coupled to the memory, that encodes the audio signal with a first
encoded sequence of code symbols representing the predetermined
message and a second encoded sequence of code symbols representing
the predetermined message, such that the second encoded sequence of
code symbols differs from the first encoded sequence of code
symbols and the second encoded sequence of code symbols is
displaced in time in the audio signal with respect to the first
encoded sequence of code symbols, wherein the first and second
encoded sequences of code symbols are inaudible when the audio
signal is reproduced audibly; and wherein the code symbols of the
first and second encoded sequences of code symbols are selected
from a predetermined set of code symbols in which the code symbols
are arranged in a predetermined order, and wherein each code symbol
of the second encoded sequence of code symbols corresponds to a
respective code symbol of the first encoded sequence of code
symbols and is selected based on the order of the respective code
symbol of the first encoded sequence of code symbols, and wherein
the first encoded sequence of code symbols has a frequency content
which differs at least in part from a frequency content of the
second encoded sequence of code symbols..Iaddend.
.Iadd.107. An apparatus according to claim 106, wherein each code
symbol of the second encoded sequence of code symbols is selected
from the predetermined set of code symbols based on a predetermined
offset in the predetermined order from the respective code symbol
of the first encoded sequence of code symbols..Iaddend.
.Iadd.108. An apparatus according to claim 107, wherein the
predetermined offset is the same for all code symbols of the second
encoded sequence of code symbols..Iaddend.
.Iadd.109. An apparatus for encoding a predetermined message in an
audio signal, comprising: a memory; an encoder that encodes the
audio signal with a first encoded sequence of code symbols
representing the predetermined message and a second encoded
sequence of code symbols representing the predetermined message,
such that the second encoded sequence of code symbols differs from
the first encoded sequence of code symbols and the second encoded
sequence of code symbols is displaced in time in the audio signal
with respect to the first encoded sequence of code symbols; and
wherein the code symbols of the first and second encoded sequences
of code symbols are selected from a predetermined set of code
symbols and each code symbol of the predetermined set of code
symbols comprises a combination of single-frequency code components
unique among all combinations of single-frequency code components
of the code symbols within the predetermined set of code symbols,
and wherein the first encoded sequence of code symbols has a
frequency content which differs at least in part from a frequency
content of the second encoded sequence of code
symbols..Iaddend.
.Iadd.110. An apparatus for encoding a predetermined message in an
audio signal, comprising: a memory; and an encoder that encodes the
audio signal with a first encoded sequence of code symbols
representing the predetermined message and a second encoded
sequence of code symbols representing the predetermined message,
such that the second encoded sequence of code symbols differs from
the first encoded sequence of code symbols and the second encoded
sequence of code symbols is displaced in time in the audio signal
with respect to the first encoded sequence of code symbols, wherein
each of the code symbols in the first encoded sequence of code
symbols comprises a first set of single frequency components and
each of the code symbols in the second encoded sequence of code
symbols comprises a second set of single frequency components, and
wherein the first encoded sequence of code symbols has a frequency
content which differs at least in part from a frequency content of
the second encoded sequence of code symbols..Iaddend.
.Iadd.111. An apparatus according to claim 110, wherein the audio
signal is further encoded with a marker symbol positioned in time
adjacent at least one of the first encoded sequence of code symbols
and the second encoded sequence of code symbols..Iaddend.
.Iadd.112. An apparatus according to claim 110, wherein the audio
signal is further encoded with a first marker symbol adjacent the
first encoded sequence of code symbols and a second marker symbol
adjacent the second encoded sequence of code symbols..Iaddend.
Description
.Iadd.CROSS-REFERENCE TO RELATED APPLICATIONS AND U.S. PATENT
DOCUMENT.Iaddend.
.Iadd.This is an application to reissue U.S. Pat. No. 6,871,180
issued Mar. 22, 2005 from application Ser. No. 09/318,045 filed May
25, 1999..Iaddend.
BACKGROUND OF THE INVENTION
The present invention relates to methods and apparatus for
extracting an information signal from an encoded audio signal.
There are various motivations to permanently or indelibly
incorporate information signals into audio signals, referred to as
"watermarking." Such an audio watermark may provide, for example,
an indication of authorship, content, lineage, existence of
copyright, or the like for the audio signals so marked.
Alternatively, other information may be incorporated into audio
signals either concerning the signal itself or unrelated to it. The
information may be incorporated in an audio signal for various
purposes, such as identification or as an address or command,
whether or not related to the signal itself.
There is considerable interest in encoding audio signals with
information to produce encoded audio signals having substantially
the same perceptible characteristics as the original unencoded
audio signals. Recent successful techniques exploit the
psychoacoustic masking effect of the human auditory system whereby
certain sounds are humanly imperceptible when received along with
other sounds.
One particularly successful utilization of the psychoacoustic
masking effect is described in U.S. Pat. No. 5,450,490 and U.S.
Pat. No. 5,764,763 (Jensen et al.) in which information is
represented by a multiple-frequency code signal which is
incorporated into an audio signal based upon the masking ability of
the audio signal. The encoded audio signal is suitable for
broadcast transmission and reception as well as for recording and
reproduction. When received the audio signal is then processed to
detect the presence of the multiple-frequency code signal.
Sometimes, only a portion of the multiple-frequency code signal,
e.g., a number of single frequency code components, inserted into
the original audio signal are detected in the received audio
signal. If a sufficient quantity of code components is detected,
the information signal itself may be recovered.
Generally, an acoustic signal having low amplitude levels will have
only minimal capacity, if any at all, to acoustically mask an
information signal. For example, such low amplitude levels can
occur during a pause in a conversation, during an interlude between
segments of music, or even within certain types of music. During a
lengthy period of low amplitude levels, it may be difficult to
incorporate a code signal in an audio signal without causing the
encoded audio signal to differ from the original in an acoustically
perceptible manner.
A further problem is the occurrence of burst errors during the
transmission or reproduction of encoded audio signals. Burst errors
may appear as temporally contiguous segments of signal error. Such
errors generally are unpredictable and substantially affect the
content of an encoded audio signal. Burst errors typically arise
from failure in a transmission channel or reproduction device due
to severe external interferences, such as an overlapping of signals
from different transmission channels, an occurrence of system power
spikes, an interruption in normal operations, an introduction of
noise contamination (intentionally or otherwise), and the like. In
a transmission system, such circumstances may cause a portion of
the transmitted encoded audio signals to be entirely unreceivable
or significantly altered. Absent retransmission of the encoded
audio signal, the affected portion of the encoded audio may be
wholly unrecoverable, while in other instances alterations to the
encoded audio signal may render the embedded information signal
undetectable. In many applications, such as radio and television
broadcasting, real-time retransmission of encoded audio signals is
simply unfeasible.
In systems for acoustically reproducing audio signals recorded on
media, a variety of factors may cause burst errors in the
reproduced acoustic signal. Commonly, an irregularity in the
recording media, caused by damage, obstruction, or wear, results in
certain portions of recorded audio signals being unreproducable or
significantly altered upon reproduction. Also, misalignment of or
interference with the recording or reproducing mechanism relative
to the recording medium can cause burst-type errors during an
acoustic reproduction of recorded audio signals. Further, the
acoustic limitations of a speaker as well as the acoustic
characteristics of the listening environment may result in spatial
irregularities in the distribution of acoustic energy. Such
irregularities may cause burst errors to occur in received acoustic
signals, interfering with code recovery.
OBJECTS AND SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide systems
and methods for detecting code symbols in audio signals which
alleviate the problems caused by periods of low signal levels and
burst errors.
It is another object of the invention to provide such systems and
methods which afford reliable operation under adverse
conditions.
It is a further object of the invention to provide such systems and
methods which are robust.
In accordance with an aspect of the present invention, systems and
methods are provided for decoding at least one message symbol
represented by a plurality of code symbols in an audio signal. The
systems and methods comprise the means for and the steps of,
respectively, receiving first and second code symbols representing
a common message symbol, the first and second code symbols being
displaced in time in the audio signal, accumulating a first signal
value representing the first code symbol and a second signal value
representing the second code symbol, and examining the accumulated
first and second signal values to detect the common message
symbol.
In accordance with another aspect of the present invention, a
system is provided for decoding at least one message symbol
represented by a plurality of code symbols in an audio signal. The
system comprises, an input device for receiving first and second
code symbols representing a common message symbol, the first and
second code symbols being displaced in time in the audio signal;
and a digital processor in communication with the input device to
receive data therefrom representing the first and second code
symbols, the digital processor being programmed to accumulate a
first signal value representing the first code symbol and a second
signal value representing the second code symbol, the digital
processor being further programmed to examine the accumulated first
and second signal values to detect the common message symbol.
In certain embodiments, the first and second signal values are
accumulated by storing the values separately and the common message
symbol is detected by examining both of the separately stored
values. The first and second signal values may represent signal
values derived from multiple other signal values, such as values of
individual code frequency components, or a single signal value,
such as a measure of the magnitude of a single code frequency
component. Moreover, a derived value may be obtained as a linear
combination of multiple signal values, such as a summation of
weighted or unweighted values, or as a non-linear function
thereof.
In further embodiments, the first and second signal values are
accumulated by producing a third signal value derived from the
first and second values. The third signal value in some embodiments
is derived through a linear combination of the first and second
signal values, such as a weighted or unweighted summation thereof,
or as a nonlinear function thereof.
Other objects, features, and advantages according to the present
invention will become apparent from the following detailed
description of certain advantageous embodiments when read in
conjunction with the accompanying drawings in which the same
components are identified by the same reference numerals.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a functional block diagram of an encoding apparatus;
FIG. 2 is a table to which reference will be made in explaining a
methodology for encoding information in an audio signal;
FIGS. 3A, 3B, and 3C are schematic diagrams which illustrate an
audio signal encoding methodology;
FIG. 4 is another table to which reference will be made in
explaining a methodology for encoding information in an audio
signal;
FIG. 5 is a block diagram illustrating a multiple-stage audio
signal encoding system;
FIG. 6 is a functional block diagram of a personal portable
meter;
FIG. 7 is a functional block diagram illustrating a decoding
apparatus;
FIG. 8 is a flowchart illustrating a methodology for retrieving an
information code from an encoded audio signal;
FIG. 9 is a schematic diagram of a circular SNR buffer used in
carrying out the methodology of FIG. 8;
FIG. 10 is a flow chart illustrating another methodology for
retrieving an information code from an encoded audio signal.
DETAILED DESCRIPTION OF CERTAIN ADVANTAGEOUS EMBODIMENTS
The present invention relates to the use of especially robust
encoding which converts information into redundant sequences of
code symbols. In certain embodiments, each code symbol is
represented by a set of different, predetermined single-frequency
code signals; however, in other embodiments different code symbols
may optionally share certain single-frequency code signals or may
be provided by a methodology which does not assign predetermined
frequency components to a given symbol. The redundant sequence of
symbols is incorporated into the audio signals to produce encoded
audio signals that are unnoticed by the listener but nevertheless
recoverable.
The redundant code symbol sequence is especially suited for
incorporation into audio signals having low masking capacity, such
as audio signals having many low amplitude portions or the like.
Additionally, when incorporated into audio signals, the redundant
sequence of code symbols resists degradation by burst errors which
affect temporally contiguous audio signals. As described
hereinabove, such errors may be the result of imperfect audio
signal recording, reproduction, and/or storage processes,
transmission of the audio signals through a lossy and/or noisy
channel, irregularities in an acoustic environment, or the
like.
To recover the encoded information in certain advantageous
embodiments, the encoded audio signals are examined in an attempt
to detect the presence of predetermined single-frequency code
components. During the encoding process, some single-frequency code
components may not have been incorporated into the audio signals in
certain signal intervals due to insufficient masking capacity in
the audio signals in these intervals. Burst errors which have
corrupted portions of the encoded audio signals can result in the
deletion of certain code signals from the encoded audio signals or
in the insertion of erroneous signals, such as noise, into the
encoded audio signals. Thus, examination of the encoded audio
signals is likely to reveal a much distorted version of the
original sequence of sets of single-frequency code signals that
represented the information.
The single-frequency code components that are recovered, along with
the erroneous additional signals that are mistakenly detected as
code signals, are processed to discern the original sequence of
code symbols, if possible. The code signal detection and processing
operations are specifically adapted to exploit the strengths of the
encoding methodology. As a result, the detection and processing
methodology of the present invention provides improved error
tolerance.
FIG. 1 is a functional block diagram of an audio signal encoder 10.
Encoder 10 implements an optional symbol generation function 12, a
symbol sequence generation function 14, a symbol encoding function
16, an acoustic masking effect evaluation/adjustment function 18,
and an audio signal inclusion function 20. Preferably encoder 10
comprises a software-controlled computer system. The computer may
be provided with an analog processor for sampling an analog audio
signal to be encoded, or may input the audio signal directly in
digital form, with or without resampling. Alternatively, encoder 10
may comprise one or more discrete signal processing components.
The symbol generation function 12, when employed, translates an
information signal into a set of code symbols. This function may be
carried out with the use of a memory device, such as a
semiconductor EPROM of the computer system, which is prestored with
a table of code symbols suitable for indexing with respect to an
information signal. An example of a table for translating an
information signal into a code symbol for certain applications is
shown in FIG. 2. The table may be stored on a hard drive or other
suitable storage device of the computer system. The symbol
generation function may also be carried out by one or more discrete
components, such as an EPROM and associated control devices, by a
logic array, by an application specific integrated circuit, or any
other suitable device or combination of devices. The symbol
generation function may also be implemented by one or more devices
which also implement one or more of the remaining functions
illustrated in FIG. 1.
The symbol sequence generating function 14 formats the symbols
produced by the symbol generating function (or input directly to
the encoder 10) into a redundant sequence of code or information
symbols. As part of the formatting process, in certain embodiments
marker and/or synchronization symbols are added to the sequence of
code symbols. The redundant sequence of code symbols is designed to
be especially resistant to burst errors and audio signal encoding
processes. Further explanation of redundant sequences of code
symbols in accordance with certain embodiments will be provided in
connection with the discussion of FIGS. 3A, 3B, and 3C below.
Preferably, the generating function 14 is implemented in a
processing device, such as a microprocessor system, or by a
dedicated formatting device, such as an application specific
integrated circuit or a logic array, by a plurality of components
or a combination of the foregoing. The symbol sequence generating
function may also be implemented by one or more devices which also
implement one or more of the remaining functions illustrated in
FIG. 1.
As noted above, the symbol sequence generating function 14 is
optional. For example, the encoding process may be carried out such
that the information signal is translated directly into a
predetermined symbol sequence, without implementing separate symbol
generating and symbol sequence generating functions.
Each symbol of the sequence of symbols thus produced is converted
by the symbol encoding function 16 into a plurality of
single-frequency code signals. In certain advantageous embodiments
the symbol encoding function is performed by means of a memory
device of the computer system, such as a semiconductor EPROM, which
is prestored with sets of single-frequency code signals that
correspond to each symbol. An example of a table of symbols and
corresponding sets of single-frequency code signals is shown in
FIG. 4.
Alternatively, the sets of code signals may be stored on a hard
drive or other suitable storage device of the computer system. The
encoding function may also be implemented by one or more discrete
components, such as an EPROM and associated control devices, by a
logic array, by an application specific integrated circuit or any
other suitable device or combination of devices. The encoding
function may also be carried out by one or more devices which also
implement one or more of the remaining functions illustrated in
FIG. 1.
In the alternative, the encoded sequence may be generated directly
from the information signal, without implementing the separate
functions 12, 14, and 16.
The acoustic masking effect evaluation/adjustment function 18
determines the capacity of an input audio signal to mask
single-frequency code signals produced by the symbol encoding
function 16. Based upon a determination of the masking ability of
the audio signal, the function 18 generates adjustment parameters
to adjust the relative magnitudes of the single-frequency code
signals so that such code signals will be rendered inaudible by a
human listener when incorporated into the audio signal. Where the
audio signal is determined to have low masking capacity, due to low
signal amplitude or other signal characteristics, the adjustment
parameters may reduce the magnitudes of certain code signals to
extremely-low levels or may nullify such signals entirely.
Conversely, where the audio signal is determined to have a greater
masking capacity, such capacity may be utilized through the
generation of adjustment parameters that increase the magnitudes of
particular code signals. Code signals having increased magnitudes
are generally more likely to be distinguishable from noise and thus
detectable by a decoding device. Further details of certain
advantageous embodiments of such evaluation/adjustment function are
set forth in U.S. Pat. No. 5,764,763 and U.S. Pat. No. 5,450,490 to
Jensen, et al., each entitled Apparatus and Methods for Including
Codes in Audio Signals and Decoding, which are incorporated herein
by reference in their entirety.
In certain embodiments, the function 18 applies the adjustment
parameters to the single-frequency code signals to produce adjusted
single-frequency code signals. The adjusted code signals are
included in the audio signal by the function 20. Alternatively, the
function 18 supplies the adjustment parameters along with the
single-frequency code signals for adjustment and inclusion in the
audio signal by the function 20. In still other embodiments, the
function 18 is combined with one or more of the functions 12, 14,
and 16 to produce magnitude-adjusted single-frequency code signals
directly.
In certain embodiments, the acoustic masking effect
evaluation/adjustment function 18 is implemented in a processing
device, such as a microprocessor system which may also implement
one or more of the additional functions illustrated in FIG. 1. The
function 18 may also be carried out by a dedicated device, such as
an application specific integrated circuit or a logic array, or by
a plurality of discrete components, or a combination of the
foregoing.
The code inclusion function 20 combines the single-frequency code
components with the audio signal to produce an encoded audio
signal. In a straightforward implementation, the function 20 simply
adds the single-frequency code signals directly to the audio
signal. However, the function 20 may overlay the code signals upon
the audio signal. Alternatively, modulator 20 may modify the
amplitudes of frequencies within the audio signal according to an
input from acoustic masking effect evaluation function 18 to
produce an encoded audio signal that includes the adjusted code
signals. Moreover, the code inclusion function may be carried out
either in the time domain or in the frequency domain. The code
inclusion function 20 may be implemented by means of an adding
circuit, or by means of a processor. This function may also be
implemented by one or more devices described above which also
implement one or more of the remaining functions illustrated in
FIG. 1.
One or more of the functions 12 through 20 may be implemented by a
single device. In certain advantageous embodiments, the functions
12, 14, 16 and 18 are implemented by a single processor, and in
still others a single processor carries out all of the functions
illustrated in FIG. 1. Moreover, two or more of the functions 12,
14, 16 and 18 may be implemented by means of a single table
maintained in an appropriate storage device.
FIG. 2 illustrates an exemplary translation table for converting an
information signal into a code symbol. As shown, an information
signal may comprise information regarding the content of, the
characteristics of, or other considerations relating to a
particular audio signal. For example, it is contemplated that an
audio signal could be modified to include an inaudible indication
that copyright is claimed in the audio program. Correspondingly, a
symbol, such as S.sub.1, may be utilized to indicate that copyright
is claimed in the particular work. Similarly, an author may be
identified with a unique symbol S.sub.2 or a broadcasting station
identified with a unique symbol S.sub.3. Further, a particular date
could be represented by a symbol S.sub.4. Of course many other
types of information could be included in an information signal and
translated into a symbol. For example, information such as
addresses, commands, encryption keys, etc., may be encoded in such
symbols. Alternatively, sets or sequences of symbols, in addition
to or instead of individual symbols, may be utilized to represent
particular types of information. As another alternative, an entire
symbolic language may be implemented to represent any type of
information signal. Also, the encoded information need not be
related to the audio signal.
FIG. 3A is a schematic diagram illustrating a stream of symbols
which might be generated by the symbol generating function 12 of
FIG. 1, while FIGS. 3B and 3C are schematic diagrams illustrating
sequences of symbols which might be generated by the symbol
sequence generating function 14 of FIG. 1 in response to the symbol
stream of FIG. 3A. In FIGS. 3A through 3C, S.sub.1, S.sub.2,
S.sub.3, and S.sub.4 are used as examples of symbols to illustrate
features of the present invention and are not meant to limit its
applicability. For example, the information represented by any one
or more of the symbols S.sub.1, S.sub.2, S.sub.3 or S.sub.4 may be
selected arbitrarily without regard to that represented by any one
or more of the other symbols.
FIG. 3B illustrates an example of a core unit of a redundant symbol
sequence representative of an input set of four symbols, S.sub.1,
S.sub.2, S.sub.3, and S.sub.4. The core unit begins with a first
message segment having sequence or marker symbol, S.sub.A, followed
by the four input data symbols, followed by three repeating message
segments each comprised of a sequence or marker symbol, S.sub.B,
and the four input symbols. For many applications, this core unit
alone is sufficiently redundant to provide the required level of
survivability. Alternatively, this core unit may itself be repeated
to increase survivability. Moreover, the core unit may have more or
less than four message segments, as well as segments having more or
less than four or five symbols.
Generalizing from this example, an input set of N symbols, S.sub.1,
S.sub.2, S.sub.3, . . . , S.sub.N-1, S.sub.N, is represented by the
redundant symbol sequence comprising S.sub.A, S.sub.1, S.sub.2,
S.sub.3, . . . S.sub.N-1, S.sub.N, followed by (P-1) repeating
segments comprising S.sub.B, S.sub.1, S.sub.2, S.sub.3, . . .
S.sub.N-1, S.sub.N. As in the example, this core unit may itself be
repeated to increase survivability. In addition, the sequence of
symbols in the message segments may be varied from segment to
segment so long as the decoder is arranged to recognize
corresponding symbols in the various segments. Moreover, different
sequence or marker symbols and combinations thereof may be
employed, and the positions of the markers with respect to the data
symbols may be arranged differently. For example, the sequence can
take the form, S.sub.1 . . . , S.sub.2, . . . , S.sub.A, . . . ,
S.sub.N or the form, S.sub.1, S.sub.2. . . , S.sub.N, S.sub.A.
FIG. 3C illustrates an example of an advantageous core unit of a
redundant symbol sequence representative of an input set of four
data symbols, S.sub.1, S.sub.2, S.sub.3, and S.sub.4. The core unit
begins with a sequence or marker symbol, S.sub.A, followed by the
four input data symbols, followed by a sequence or marker symbol,
S.sub.B, followed by S.sub.(1+.beta.) mod M, S.sub.(2+.beta.) mod
M, S.sub.(3+.beta.) mod M, S.sub.(4+.beta.) mod M, where M is the
number of different symbols in the available symbol set and where
.beta. is an offset having a value between O and M. In an
advantageous embodiment, the offset .beta. is selected as a CRC
checksum. In still other embodiments, the value of the offset
.beta. is varied from time to time to encode additional information
in the message. For example, if the offset can vary from 0 to 9,
nine different information states can be encoded in the offset.
Generalizing from this example, an input set of N symbols, S.sub.1,
S.sub.2, S.sub.3, . . . S.sub.N-1, S.sub.N, is represented by the
redundant symbol sequence comprising S.sub.A, S.sub.1, S.sub.2,
S.sub.3, . . . S.sub.N-1, S.sub.N, S.sub.B, S.sub.(1+.beta.) mod M,
S.sub.(2+.beta.) mod M, S.sub.(3+.beta.) mod M, . . .
S.sub.(N-1+.beta.) mod M, S.sub.(N+.beta.)mod M. That is, the same
information is represented by two or more different symbols in the
same core unit and recognized according to their order therein. In
addition, these core units may themselves be repeated to increase
survivability. Since the same information is represented by
multiple different symbols, the coding is made substantially more
robust. For example, the structure of an audio signal can mimic the
frequency component of one of the data symbols S.sub.N, but the
likelihood that the audio signal will also mimic its corresponding
offset S.sub.(N+.beta.) mod M at its predetermined occurrence is
very much lower. Also, since the offset is the same for all symbols
within a given segment, this information provides a further check
on the validity of the detected symbols within that segment.
Consequently, the encoding format of FIG. 3C substantially reduces
the likelihood of false detections induced by the structure of the
audio signal.
A particular strength of the redundant sequence exemplified in FIG.
3 is its utilization of the input symbols in their original order
followed by (a) a different arrangement of the input symbols, (b)
an arrangement of symbols that includes other symbols in place of
one or more of the input symbols, with or without rearrangement of
input symbol order, or (c) an arrangement of symbols different from
the input symbols. Arrangements (b) and (c) are particularly robust
since, upon symbol encoding, an increased diversity of
single-frequency code signals is achieved. Assuming that the input
symbols are encoded collectively from among a first group of code
signals, symbols in arrangements (b) and (c) will be encoded with
another group of code signals which to some extent does not overlap
the first group. A greater diversity of code signals will generally
increase the likelihood that some code signals are within the
masking capacity of the audio signal.
The table of FIG. 4 illustrates an exemplary conversion for a
sequence or marker symbol, S.sub.A, a sequence or marker symbol,
S.sub.B, and N data symbols, S.sub.1, S.sub.2, S.sub.3, . . . ,
S.sub.N-1, S.sub.N, into corresponding sets of M single-frequency
code signals f.sub.1x, f.sub.2x, f.sub.3x, . . . , f.sub.[M-1]x,
f.sub.Mx, where x references the identifying subscript of the
particular symbol. Although the single-frequency code signals may
occur throughout the frequency range of the audio signal and, to
some extent, outside such frequency range, the code signals of this
embodiment are within the frequency range 500 Hz to 5500 Hz but may
be selected as a different frequency range. In one embodiment, the
sets of M single-frequency code signals may share certain
single-frequency code signals; however, in a preferred embodiment,
the single-frequency code signals are completely non-overlapping.
Moreover, it is not necessary that all symbols be represented by
the same number of frequency components.
FIG. 5 illustrates a multiple-stage audio signal encoding system
50. This system implements multiple audio signal encoders to
successively encode an audio signal 52 as it travels along a
typical audio signal distribution network. At each stage of
distribution, the audio signal is successively encoded with an
information signal pertinent to the particular stage. Preferably,
the successive encodings of the respective information signals do
not produce code signals that overlap in frequency. Nevertheless,
due to the robust nature of the encoding methodology, partial
overlap among the frequency components of the respective encoded
information signals is tolerable. System 50 includes a recording
facility 54; a broadcaster 66; a relay station 76; audio signal
encoders 58, 70, and 80; an audio signal recorder 62; a listener
facility 86; and an audio signal decoder 88.
Recording facility 54 includes apparatus for receiving and encoding
audio signals and recording encoded audio signals upon a storage
medium. Specifically, facility 54 includes audio signal encoder 58
and audio signal recorder 62. Audio signal encoder 58 receives an
audio signal feed 52 and a recording information signal 56 and
encodes audio signal 52 with information signal 56 to produce an
encoded audio signal 60. Audio signal feed 52 may be produced by
any conventional source of audio signals such as a microphone, an
apparatus for reproducing recorded audio signals, or the like.
Recording information signal 56 preferably comprises information
regarding audio signal feed 52, such as its authorship, content, or
lineage, or the existence of copyright, or the like. Alternatively,
recording information signal 56 may comprise any type of data.
Recorder 62 is a conventional device for recording encoded audio
signals 60 upon a storage medium which is suitable for distribution
to one or more broadcasters 66. Alternatively, audio signal
recorder 62 may be omitted entirely. Encoded audio signals 60 may
be distributed via distribution of the recorded storage media or
via a communication link 64. Communication link 64 extends between
recording facility 54 and broadcaster 66 and may comprise a
broadcast channel, a microwave link, a wire or fiber optic
connection, or the like.
Broadcaster 66 is a broadcasting station that receives encoded
audio signals 60, further encodes such signals 60 with a
broadcaster information signal 68 to produce a twice-encoded audio
signal 72, and broadcasts the twice-encoded audio signal 72 along a
transmission path 74. Broadcaster 66 includes an audio signal
encoder 70 which receives encoded audio signal 60 from recording
facility 54 and a broadcaster information signal 68. Broadcaster
information signal 68 may comprise information regarding
broadcaster 66, such as an identification code, or regarding the
broadcasting process, such as the time, date or characteristics of
the broadcast, the intended recipient(s) of the broadcast signal,
or the like. Encoder 70 encodes encoded audio signal 60 with
information signal 68 to produce twice-encoded audio signal 72.
Transmission path 74 extends between broadcaster 66 and relay
station 76 may comprise a broadcast channel, a microwave link, a
wire or fiber optic connection, or the like.
Relay station 76 receives a twice-encoded audio signal 72 from
broadcaster 66, further encodes that signal with a relay station
information signal 78, and transmits the thrice-encoded audio
signal 82 to a listener facility 86 via a transmission path 84.
Relay station 76 includes an audio signal encoder 80 which receives
twice-encoded audio signal 72 from broadcaster 66 and a relay
station information signal 78. Relay station information signal 78
preferably comprises information regarding relay station 76, such
as an identification code, or regarding the process of relaying the
broadcast signal, such as the time, date or characteristics of the
relay, the intended recipient(s) of the relayed signal, or the
like. Encoder 80 encodes twice-encoded audio signal 72 with relay
station information signal 78 to produce thrice-encoded audio
signal 82. Transmission path 84 extends between relay station 76
and listener facility 86 and may comprise a broadcast channel, a
microwave link, a wire or fiber optic connection, or the like.
Optionally, transmission path 84 may be an acoustic transmission
path.
Listener facility 86 receives thrice-encoded audio signal 82 from
relay station 76. In audience estimate applications, listener
facility 86 is located where a human listener may perceive an
acoustic reproduction of audio signal 82. If audio signal 82 is
transmitted as an electromagnetic signal, listener facility 86
preferably includes a device for acoustically reproducing that
signal for the human listener. However, if audio signal 82 is
stored upon a storage medium, listener facility 86 preferably
includes a device for reproducing signal 82 from the storage
medium.
In other applications, such as music identification and commercial
monitoring, a monitoring facility is employed rather than listener
86. In such a monitoring facility, the audio signal 82 preferably
is processed to receive the encoded message without acoustic
reproduction.
Audio signal decoder 88 may receive thrice encoded audio signal 82
as an audio signal or, optionally, as an acoustic signal. Decoder
88 decodes audio signal 82 to recover one or more of the
information signals encoded therein. Preferably, the recovered
information signal(s) are processed at listener facility 86 or
recorded on a storage medium for later processing.
Alternatively, the recovered information signal(s) may be converted
into images for visual display to the listener.
In an alternate embodiment, recording facility 54 is omitted from
system 50. Audio signal feed 52, representing, for example, a live
audio performance, is provided directly to broadcaster 66 for
encoding and broadcast. Accordingly, broadcaster information signal
68 may further comprise information regarding audio signal feed 52,
such as its authorship, content, or lineage, or the existence of
copyright, or the like.
In another alternate embodiment, relay station 76 is omitted from
system 50. Broadcaster 66 provides twice-encoded audio signal 72
directly to listener 86 via transmission path 74 which is modified
to extend therebetween. As a further alternative, both recording
facility 54 and relay station 76 may be omitted from system 50.
In another alternate embodiment, broadcaster 66 and relay station
76 are omitted from system 50. Optionally, communication link 64 is
modified to extend between recording facility 54 and listener
facility 86 and to carry encoded audio signal 60 therebetween.
Preferably, audio signal recorder 62 records encoded audio signal
60 upon a storage medium which is thereafter conveyed to listener
facility 86. An optional reproduction device at listener facility
86 reproduces the encoded audio signal from the storage medium for
decoding and/or acoustic reproduction.
FIG. 6 provides an example of a personal portable meter 40 for use
in audience estimate applications. The meter 90 includes a housing
92, illustrated in phantom lines, having a size and shape
permitting it to be carried on the person of an audience member.
For example, the housing may have the same size and shape as a
pager unit.
A microphone 93 is within the housing 92 and serves as an acoustic
transducer to transduce received acoustic energy, including encoded
audio signals, to analog electrical signals. The analog signals are
converted to digital by an analog to digital converter and the
digital signals are then supplied to a digital signal processor
(DSP) 95. The DSP 95 implements a decoder in accordance with the
present invention in order to detect the presence of predetermined
codes in the audio energy received by the microphone 93 indicating
that the person carrying the personal portable meter 90 has been
exposed to a broadcast of a certain station or channel. If so, the
DSP 95 stores a signal representing such detection in its internal
memory along with an associated time signal.
The meter 90 also includes a data transmitter/receiver, such as an
infrared transmitter/receiver 97 coupled with the DSP 95. The
transmitter/receiver 97 enables the DSP 95 to provide its data to a
facility for processing such data from multiple meters 90 to
produce audience estimates, as well as to receive instructions and
data, for example, to set up the meter 90 for carrying out a new
audience survey.
Decoders in accordance with certain advantageous embodiments of the
present invention are illustrated by the functional block diagram
of FIG. 7. An audio signal which may be encoded as described
hereinabove with a plurality of code symbols, is received at an
input 102. The received audio signal may be a broadcast, internet
or otherwise communicated signal, or a reproduced signal. It may be
a direct coupled or an acoustically coupled signal. From the
following description in connection with the accompanying drawings,
it will be appreciated that the decoder 100 is capable of detecting
codes in addition to those arranged in the formats disclosed
hereinabove.
For received audio signals in the time domain, the decoder 100
transforms such signals to the frequency domain by means of a
function 106. The function 106 preferably is performed by a digital
processor implementing a fast Fourier transform (FFT) although a
direct cosine transform, a chirp transform or a Winograd transform
algorithm (WFTA) may be employed in the alternative. Any other
time-to-frequency-domain transformation function providing the
necessary resolution may be employed in place of these. It will be
appreciated that in certain implementations, the function 106 may
also be carried out by analog or digital filters, by an application
specific integrated circuit, or any other suitable device or
combination of devices. The function 106 may also be implemented by
one or more devices which also implement one or more of the
remaining functions illustrated in FIG. 7.
The frequency domain-converted audio signals are processed in a
symbol values derivation function 110, to produce a stream of
symbol values for each code symbol included in the received audio
signal. The produced symbol values may represent, for example,
signal energy, power, sound pressure level, amplitude, etc.,
measured instantaneously or over a period of time, on an absolute
or relative scale, and may be expressed as a single value or as
multiple values. Where the symbols are encoded as groups of single
frequency components each having a predetermined frequency, the
symbol values preferably represent either single frequency
component values or one or more values based on single frequency
component values.
The function 110 may be carried out by a digital processor, such as
a digital signal processor (DSP) which advantageously carries out
some or all of the other functions of decoder 100. However, the
function 110 may also be carried out by an application specific
integrated circuit, or by any other suitable device or combination
of devices, and may be implemented by apparatus apart from the
means which implement the remaining functions of the decoder
100.
The stream of symbol values produced by the function 110 are
accumulated over time in an appropriate storage device on a
symbol-by-symbol basis, as indicated by the function 116. In
particular, the function 116 is advantageous for use in decoding
encoded symbols which repeat periodically, by periodically
accumulating symbol values for the various possible symbols. For
example, if a given symbol is expected to recur every X seconds,
the function 116 may serve to store a stream of symbol values for a
period of nX seconds (n>1), and add to the stored values of one
or more symbol value streams of nX seconds duration, so that peak
symbol values accumulate over time, improving the signal-to-noise
ratio of the stored values.
The function 116 may be carried out by a digital processor, such as
a DSP, which advantageously carries out some or all of the other
functions of decoder 100. However, the function 110 may also be
carried out using a memory device separate from such a processor,
or by an application specific integrated circuit, or by any other
suitable device or combination of devices, and may be implemented
by apparatus apart from the means which implements the remaining
functions of the decoder 100.
The accumulated symbol values stored by the function 116 are then
examined by the function 120 to detect the presence of an encoded
message and output the detected message at an output 126. The
function 120 can be carried out by matching the stored accumulated
values or a processed version of such values, against stored
patterns, whether by correlation or by another pattern matching
technique. However, the function 120 advantageously is carried out
by examining peak accumulated symbol values and their relative
timing, to reconstruct their encoded message. This function may be
carried out after the first stream of symbol values has been stored
by the function 116 and/or after each subsequent stream has been
added thereto, so that the message is detected once the
signal-to-noise ratios of the stored, accumulated streams of symbol
values reveal a valid message pattern.
FIG. 8 is a flow chart for a decoder according to one advantageous
embodiment of the invention implemented by means of a DSP. Step 130
is provided for those applications in which the encoded audio
signal is received in analog form, for example, where it has been
picked up by a microphone (as in FIG. 6 embodiment) or an RF
receiver.
The decoder of FIG. 8 is particularly well adapted for detecting
code symbols each of which includes a plurality of predetermined
frequency components, e.g. ten components, as within a frequency
range of 1000 Hz to 3000 Hz. It is designed specifically to detect
a message having the sequence illustrated in FIG. 3C wherein each
symbol occupies an interval of one half-second. In this exemplary
embodiment, it is assumed that the symbol set consists of twelve
symbols, each having ten predetermined frequency components, none
of which is shared with any other symbol of the symbol set. It will
be appreciated that the FIG. 8 decoder may readily be modified to
detect different numbers of code symbols, different numbers of
components, different symbol sequences and symbol durations, as
well as components arranged in different frequency bands.
In order to separate the various components, the DSP repeatedly
carries out FFTs on audio signal samples falling within successive,
predetermined intervals. The intervals may overlap, although this
is not required. In an exemplary embodiment, ten overlapping FFT's
are carried out during each second of decoder operation.
Accordingly, the energy of each symbol period falls within five FFT
periods. The FFT's may be windowed, although this may be omitted in
order to simplify the decoder. The samples are stored and, when a
sufficient number are thus available, a new FFT is performed, as
indicated by steps 134 and 138.
In this embodiment, the frequency component values are produced on
a relative basis. That is, each component value is represented as a
signal-to-noise ratio (SNR), produced as follows. The energy within
each frequency bin of the FFT in which a frequency component of any
symbol can fall provides the numerator of each corresponding SNR
Its denominator is determined as an average of adjacent bin values.
For example, the average of seven of the eight surrounding bin
energy values may be used, the largest value of the eight being
ignored in order to avoid the influence of a possible large bin
energy value which could result, for example, from an audio signal
component in the neighborhood of the code frequency component.
Also, given that a large energy value could also appear in the code
component bin, for example, due to noise or an audio signal
component, the SNR is appropriately limited. In this embodiment, if
SNR=>6.0, then SNR is limited to 6.0, although a different
maximum value may be selected.
The ten SNR's of each FFT and corresponding to each symbol which
may be present, are combined to form symbol SNR's which are stored
in a circular symbol SNR buffer, as indicated in step 142 and
illustrated schematically in FIG. 9. In certain embodiments, the
ten SNR's for a symbol are simply added, although other ways of
combining the SNR's may be employed.
As indicated by FIG. 9, the symbol SNR's for each of the twelve
symbols A, B and 0-9, are stored in the symbol SNR buffer as
separate sequences, one symbol SNR for each FFT for 50 .mu.l FFT's.
After the values produced in the 50 FFT's have been stored in the
symbol SNR buffer, new symbol SNR's are combined with the
previously stored values, as described below.
When the symbol SNR buffer is filled, this is detected in a step
146. In certain advantageous embodiments, the stored SNR's are
adjusted to reduce the influence of noise in a step 152, although
this step is optional in many applications. In this optional step,
a noise value is obtained for each symbol (row) in the buffer by
obtaining the average of all stored symbol SNR's in the respective
row each time the buffer is filled. Then, to compensate for the
effects of noise, this average or "noise" value is subtracted from
each of the stored symbol SNR values in the corresponding row. In
this manner, a "symbol" appearing only briefly, and thus not a
valid detection, is averaged out over time. Referring also to FIG.
3C, in order to avoid inflating the noise value at the decoder,
preferably the encoding scheme is constrained so that the same
symbol does not appear twice in the first half of the message
(i.e., within symbol sequence S.sub.A, S.sub.1, S.sub.2, S.sub.3,
S.sub.4).
After the symbol SNR's have been adjusted by subtracting the noise
level, the decoder attempts to recover the message by examining the
pattern of maximum SNR values in the buffer in a step 156. In
certain embodiments, the maximum SNR values for each symbol are
located in a process of successively combining groups of five
adjacent SNR's, by weighting the values in the sequence in
proportion to the sequential weighting (6 10 10 10 6) and then
adding the weighted SNR's to produce a comparison SNR centered in
the time period of the third SNR in the sequence. This process is
carried out progressively throughout the fifty FFT periods of each
symbol. For example, a first group of five SNR's for the "A" symbol
in FFT periods 1 through 5 are weighted and added to produce a
comparison SNR for FFT period 3. Then a further comparison SNR is
produced using the SNR's from FFT periods 2-6, and so on until
comparison values have been obtained centered on FFT periods 3
through 48. However, other means may be employed for recovering the
message. For example, either more or less than five SNR's may be
combined, they may be combined without weighing, or they may be
combined in a non-linear fashion.
After the comparison SNR values have been obtained, the decoder
examines the comparison SNR values for a message pattern. First,
the marker code symbols S.sub.A and S.sub.B are located. Once this
information is obtained, the decoder attempts to detect the peaks
of the data symbols. The use of a predetermined offset between each
data symbol in the first segment and the corresponding data symbol
in the second segment provides a check on the validity of the
detected message. That is, if both markers are detected and the
same offset is observed between each data symbol in the first
segment and its corresponding data symbol in the second segment, it
is highly likely that a valid message has been received.
With reference both to FIGS. 3C and 9, assuming that the beginning
of the buffer corresponds with the beginning of the message (which
usually is not the case), a peak P of the comparison SNR's for the
"A" symbol should appear in the third FFT period, as indicated.
Then the decoder will expect the next peak to appear in the
position corresponding to the first data symbol 0-9 in the eighth
FFT period. In this example, it is assumed that the first data
symbol is "3". If the last data symbol is "4" and the value of 6 is
2, the decoder will find a peak of the symbol "6" in FFT period 48,
as indicated in FIG. 9. If the message is thus detected (i.e.,
markers detected with data symbols appearing where expected and
with the same offset throughout), as indicated in steps 162 and
166, the message is logged or output and the SNR buffer is
cleared.
However, if the message is not thus found, a further fifty
overlapping FFT's are carried out on the following portions of the
audio signal and the symbol SNR's so produced are added to those
already in the circular buffer. The noise adjustment process is
carried out as before and the decoder attempts to detect the
message pattern again. This process is repeated continuously until
a message is detected. In the alternative, the process may be
carried out a limited number of times.
It will be apparent from the foregoing to modify the operation of
the decoder depending on the structure of the message, its timing,
its signal path, the mode of its detection, etc., without departing
from the scope of the present invention. For example, in place of
storing SNR's, FFT results may be stored directly for detecting a
message.
FIG. 10 is a flow chart for another decoder according to a further
advantageous embodiment likewise implemented by means of a DSP. The
decoder of FIG. 10 is especially adapted to detect a repeating
sequence of five code symbols consisting of a marker symbol
followed by four data symbols wherein each of the code symbols
includes a plurality of predetermined frequency components and has
a duration of one-half second in the message sequence. It is
assumed that each symbol is represented by ten unique frequency
components and that the symbol set includes twelve different
symbols A, B and 0-9, as in the code of FIG. 3C. However, the FIG.
9 embodiment may readily be modified to detect any number of
symbols, each represented by one or more frequency components.
Steps employed in the decoding process illustrated in FIG. 10 which
correspond to those of FIG. 8 are indicated by the same reference
numerals, and these steps consequently are not further described.
The FIG. 10 embodiment uses a circular buffer which is twelve
symbols wide by 150 FFT periods long. Once the buffer has been
filled, new symbol SNRs each replace what are than the oldest
symbol SNR values. In effect, the buffer stores a fifteen second
window of symbol SNR values.
As indicated in step 174, once the circular buffer is fill, its
contents are examined in a step 178 to detect the presence of the
message pattern. Once full, the buffer remains full continuously,
so that the pattern search of step 178 may be carried out after
every FFT.
Since each five symbol message repeats every 21/2 seconds, each
symbol repeats at intervals of 21/2 seconds or every 25 FFT's. In
order to compensate for the effects of burst errors and the like,
the SNR's R.sub.1 through R.sub.150 are combined by adding
corresponding values of the repeating messages to obtain 25
combined SNR values SNR.sub.n, n=1, 2 . . . 25, as follows:
.times..times..times. ##EQU00001##
Accordingly, if a burst error should result in the loss of a signal
interval i, only one of the six message intervals will have been
lost, and the essential characteristics of the combined SNR values
are likely to be unaffected by this event.
Once the combined SNR values have been determined, the decoder
detects the position of the marker symbol's peak as indicated by
the combined SNR values and derives the data symbol sequence based
on the marker's position and the peak values of the data
symbols.
Once the message has thus been formed, as indicated in steps 182
and 183, the message is logged. However, unlike the embodiment of
FIG. 8 the buffer is not cleared. Instead, the decoder loads a
further set of SNR's in the buffer and continues to search for a
message.
As in the decoder of FIG. 8, it will be apparent from the foregoing
to modify the decoder of FIG. 10 for different message structures,
message timings, signal paths, detection modes, etc., without
departing from the scope of the present invention. For example, the
buffer of the FIG. 10 embodiment may be replaced by any other
suitable storage device; the size of the buffer may be varied; the
size of the SNR values windows may be varied; and/or the symbol
repetition time may vary. Also, instead of calculating and storing
signal SNR's to represent the respective symbol values, a measure
of each symbol's value relative to the other possible symbols, for
example, a ranking of each possible symbol's magnitude, is instead
used in certain advantageous embodiments.
In a further variation which is especially useful in audience
measurement applications, a relatively large number of message
intervals are separately stored to permit a retrospective analysis
of their contents to detect a channel change. In another
embodiment, multiple buffers are employed, each accumulating data
for a different number of intervals for use in the decoding method
of FIG. 8. For example, one buffer could store a single message
interval, another two accumulated intervals, a third four intervals
and a fourth eight intervals. Separate detections based on the
contents of each buffer are then used to detect a channel
change.
Although illustrative embodiments of the present invention and
modifications thereof have been described in detail herein, it is
to be understood that this invention is not limited to these
precise embodiments and modifications, and that other modifications
and variations may be effected therein by one skilled in the art
without departing from the scope and spirit of the invention as
defined by the appended claims.
* * * * *
References