U.S. patent application number 11/071935 was filed with the patent office on 2005-08-25 for controlling fading and surround signal level.
Invention is credited to Barksdale, Tobe, Salvador, Eduardo T..
Application Number | 20050185806 11/071935 |
Document ID | / |
Family ID | 36570515 |
Filed Date | 2005-08-25 |
United States Patent
Application |
20050185806 |
Kind Code |
A1 |
Salvador, Eduardo T. ; et
al. |
August 25, 2005 |
Controlling fading and surround signal level
Abstract
Preserving an audio signal in an audio system includes selecting
a first audio signal from a plurality of audio signals. The first
audio signal is applied to a first transducer. Mix a portion of the
first audio signal with a second audio signal from the plurality of
audio signals to provide a mixed audio signal. A gain of the first
audio signal that is applied to the first transducer is decreased
while a portion of the mixed audio signal is applied to a second
transducer to preserve at least a portion of the first audio
signal.
Inventors: |
Salvador, Eduardo T.;
(Cambridge, MA) ; Barksdale, Tobe; (Bolton,
MA) |
Correspondence
Address: |
FISH & RICHARDSON PC
225 FRANKLIN ST
BOSTON
MA
02110
US
|
Family ID: |
36570515 |
Appl. No.: |
11/071935 |
Filed: |
March 4, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11071935 |
Mar 4, 2005 |
|
|
|
10367251 |
Feb 14, 2003 |
|
|
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Current U.S.
Class: |
381/119 ;
381/307 |
Current CPC
Class: |
H04R 2499/13 20130101;
H04S 7/00 20130101; H04S 2400/13 20130101; H04S 7/30 20130101 |
Class at
Publication: |
381/119 ;
381/307 |
International
Class: |
H04B 001/00; H04R
005/00 |
Claims
What is claimed is:
1. A method for preserving an audio signal in an audio system
having at least a first transducer and a second transducer and a
plurality of audio signals, the method comprising: selecting a
first audio signal from the plurality of audio signals, the first
audio signal being applied to the first transducer; mixing a
portion of the first audio signal with a second audio signal from
the plurality of audio signals to generate a mixed audio signal;
and decreasing a gain of the first audio signal applied to the
first transducer while applying a portion of the mixed audio signal
to the second transducer to preserve at least a portion of the
first audio signal.
2. The method of claim 1 further comprising modifying a gain of the
second audio signal prior to mixing the portion of the first audio
signal into the second audio signal.
3. The method of claim 1 wherein the first audio signal comprises a
surround sound signal.
4. The method of claim 1 wherein the first audio signal comprises a
center channel signal.
5. The method of claim 1 further comprising mixing at least a
portion of a third audio signal from the plurality of audio signals
into a portion of a fourth audio signal from the plurality of audio
signals to generate another mixed audio signal.
6. The method of claim 1 wherein the decreasing the gain of the
first audio signal applied to the first transducer comprises
fading-out the first audio signal.
7. The method of claim 1 wherein the applying the portion of the
mixed audio signal to the second transducer comprises fading-in the
mixed audio signal.
8. The method of claim 1 wherein the mixing further comprises
determining mixing coefficients for at least one of the following,
the first audio signal and the second audio signal.
9. An audio system having at least first and second transducers
comprising: an audio source of a plurality of audio signals, the
plurality of audio signals comprising a first audio signal that is
applied to the first transducer; a processor that mixes a portion
of the first audio signal with a second audio signal from the
plurality of audio signals to generate a mixed audio signal; and a
control that decreases a gain of the first audio signal applied to
the first transducer while applying a portion of the mixed audio
signal to the second transducer to preserve at least a portion of
the first audio signal.
10. The audio system of claim 9 wherein the control comprises a
fader control.
11. The audio system of claim 9 wherein the audio source includes
discrete audio signals.
12. The audio system of claim 9 wherein at least one of the
plurality of audio signals comprises a surround signal.
13. The audio system of claim 9 wherein at least one of the
plurality of audio signals comprises a center channel signal.
14. The audio system of claim 9 wherein the fader control comprises
a rotary control.
15. The audio system of claim 9 wherein the fader control comprises
a linear control.
16. An apparatus for preserving an audio signal in an audio system
having a plurality of audio signals, the apparatus comprising: a
processor that receives the plurality of audio signals, the
processor mixing a portion of a first audio signal from the
plurality of audio signals with a second audio signal from the
plurality of audio signals to provide a mixed audio signal; and a
control that decreases a gain of the first audio signal while at
least sustaining the mixed audio signal to preserve at least a
portion of the first audio signal.
17. The apparatus of claim 16 wherein the control comprises a fader
control.
18. The apparatus of claim 16 wherein at least one of the plurality
of audio signals comprises a surround signal.
19. The apparatus of claim 16 wherein at least one of the plurality
of audio signals comprises a center channel signal.
20. The apparatus of claim 16 wherein the fader control comprises a
rotary control.
21. The apparatus of claim 16 wherein the fader control comprises a
linear control.
22. A fader control for first and second audio signals comprising:
a first control region comprising a pure fading region constructed
and arranged to establish a gain of the first audio signal being
decreased in the pure fading region while a gain of the second
audio signal is at least preserved; and a second control region
that is located adjacent to the first control region, the gain of
the first audio signal being decreased in the second control region
while a gain of a first mixed signal is at least preserved, the
first mixed signal comprising a portion of the first audio signal
and a portion of the second audio signal.
23. The fader control of claim 22 wherein at least one of the first
and the second audio signals comprises a surround signal.
24. The fader control of claim 22 wherein at least one of the first
and the second audio signals comprises a center channel signal.
25. The fader control of claim 22 wherein at least one of the first
and the second audio signals comprises a front channel signal.
26. The fader control of claim 22 wherein the first audio signal
comprises a surround signal and the second audio signal comprises a
front channel signal.
27. A fader control for a plurality of audio signals comprising: a
first control region constructed and arranged to establish a gain
of the first audio signal being decreased in the first control
region while a gain of a first mixed signal is increased, the first
mixed signal comprising a portion of the first audio signal and a
portion of a second audio signal; and a second control region that
is located adjacent to the first control region constructed and
arranged to establish, a gain of a third audio signal being
decreased in the second control region while a gain of a second
mixed signal is increased, the second mixed signal comprising a
portion of the third audio signal and a portion of a fourth audio
signal.
28. The fader control of claim 27 further comprising a third
control region that is located between the first and the second
control region constructed and arranged to establish, a pure fading
function in the third control region.
29. The fader control of claim 27 constructed and arranged to
establish a center position that is located between the first and
the second control regions, the center position comprising a
neutral fading position.
30. The fader control of claim 27 wherein at least one of the
first, second, third, and fourth audio signals comprises a surround
signal.
31. The fader control of claim 27 wherein at least one of the
first, second, third, and fourth audio signals comprises a center
channel signal.
32. The fader control of claim 27 wherein the first audio signal
comprises a surround signal and the second audio signal comprises a
front channel signal.
33. The fader control of claim 27 wherein the third audio signal
comprises a center channel signal and the fourth audio signal
comprises a surround signal.
34. A method for determining a position of a fader control of an
audio system, the method comprising: determining a ratio of the
front signal to the rear signal.
35. The method of claim 34 further comprising adjusting the
position of the fader control.
36. The method of claim 34 further comprising establishing a fade
contour with a model of fader gain relative to the ratio of the
front signal to the rear signal.
37. The method of claim 34 further comprising establishing a fade
contour with a lookup table of fader gain relative to the ratio of
the front signal to the rear signal.
38. The method of claim 34 further comprising taking a weighted
average of the front signal and the rear signal.
39. An apparatus for preserving an audio signal in an audio system
having at least first and second transducers and a source of audio
signals, the apparatus comprising: means for selecting a first
audio signal from the plurality of audio signals, the first audio
signal being applied to the first transducer; means for mixing a
portion of the first audio signal with a second audio signal from
the plurality of audio signals to generate a mixed audio signal;
and means for decreasing a gain of the first audio signal applied
to the first transducer while applying a portion of the mixed audio
signal to the second transducer to preserve at least a portion of
the first audio signal.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This patent application is a continuation-in-part (CIP) of
U.S. patent application Ser. No. 10/367,251, filed on Feb. 14,
2003, entitled Controlling Fading and Surround Signal Level, the
entire disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] Audio systems with surround sound features are prevalent in
theaters, home entertainment systems, and automobiles. In general,
surround sound features enhance the overall listening experience by
increasing the aural stimulations associated with music, motion
picture soundtracks, and other audio performances. The surround
sound capability is provided by using a collection of spatially
diverse transducers. Typically, primary (or front) transducers are
located in front of the listener or audience and surround sound
transducers are located behind and/or to the sides of the listener
or audience. Surround sound processing of an audio input controls
the signal that is sent to each transducer and causes each
transducer to produce a different audio output. As a result,
listeners may be presented with the sensation of being seemingly
surrounded by sound and/or with the sensation of sound originating
from a particular direction.
SUMMARY OF THE INVENTION
[0003] In one aspect, systems and methods are described here for
providing a single degree of freedom (DOF) control for adjusting
multiple audio functions. In particular, a first function may be
performed on a first set of signals over a first range of control
positions, and one or more other functions may be performed on
another set of signals in other ranges of control positions. The
number of signals controlled in each range may be different.
[0004] In one implementation, a single control device may be used
to control both surround signal level and image fader functionality
in a surround sound application. The control device performs
surround signal level control over a first range of control
operation, and performs a fader function over one or more other
ranges of control operation. The control device operates only on
the surround signal or signals over a portion of an operating range
for the control device, and operates on the surround signals and
other signals (which may include, e.g., front left, center, and
front right signals) over other portions of the operating range.
The control device accomplishes both functions in a natural and
intuitive manner.
[0005] Systems and techniques are provided for using a single
control device to control a surround system that includes multiple
input signals and multiple spatially diverse transducers. The
operating range of the control device may be divided into two or
more control regions. Each region may correspond to a different
control function. In one implementation, a first control region may
control a strength of one or more audio surround source signals
relative to one or more audio front source signals. A second
control region may control mixing of the audio surround source
signals and the audio front source signals in addition to
controlling the relative strengths of the audio surround source
signals and the audio front source signals. The controlled mixing
of the audio surround source signals can be used to preserve one or
more of the audio signals in the audio system.
[0006] In one aspect, a method for preserving an audio signal in an
audio system includes selecting a first audio signal from a
plurality of audio signals. The first audio signal is applied to a
first transducer. The method also includes mixing a portion of the
first audio signal with a second audio signal from the plurality of
audio signals to generate a mixed audio signal. A gain of the first
audio signal that is applied to the first transducer is decreased
while a portion of the mixed audio signal is applied to a second
transducer to preserve at least a portion of the first audio
signal. Decreasing of the gain of the first audio signal can be
achieved by fading-out the first audio signal. Applying the portion
of the mixed audio signal to the second transducer can be achieved
by fading-in the mixed audio signal.
[0007] A gain of the second audio signal can be modified prior to
mixing the portion of the first audio signal into the second audio
signal. The first audio signal can be a surround sound signal or a
center channel signal, for example.
[0008] In one example, a portion of a third audio signal from the
plurality of audio signals is mixed into a portion of a fourth
audio signal from the plurality of audio signals to generate
another mixed audio signal. The mixing can include determining
mixing coefficients for at least one of the first audio signal and
the second audio signal.
[0009] In another aspect, an audio system according to the
invention includes an audio source that generates a plurality of
audio signals. The plurality of audio signals includes a first
audio signal that is applied to a first transducer. A processor
mixes a portion of the first audio signal with a second audio
signal from the plurality of audio signals to generate a mixed
audio signal. A fader control decreases a gain of the first audio
signal applied to the first transducer while applying a portion of
the mixed audio signal to a second transducer to preserve at least
a portion of the first audio signal.
[0010] The fader control can include a control region having a pure
fade function. The processor can be a surround sound processor. The
audio source can generate discrete audio signals. One or more of
the audio signals can be a surround signal and/or a center channel
signal. The fader control can be a rotary control or a linear
control.
[0011] In another aspect, the invention is embodied in an apparatus
for preserving an audio signal in an audio system. The apparatus
includes a processor that receives a plurality of audio signals.
The processor mixes a portion of a first audio signal from the
plurality of audio signals with a second audio signal from the
plurality of audio signals to generate a mixed audio signal. A
fader control decreases a gain of the first audio signal while
increasing a gain of the mixed audio signal to preserve at least a
portion of the first audio signal.
[0012] The fader control can include a control region having a pure
fade function. The processor can include a surround sound
processor. One or more of the plurality of audio signals can
include a surround signal and/or a center channel signal. The fader
control can include a rotary control or a linear control.
[0013] In one aspect, the invention is embodied in a fader control.
The fader control includes a first control region having a pure
fading region. A gain of a first audio signal is decreased in the
pure fading region while a gain of a second audio signal is at
least preserved. A second control region is located adjacent to the
first control region. The gain of the first audio signal is
decreased in the second control region while a gain of a first
mixed signal is at least preserved. The first mixed signal includes
a portion of the first audio signal and a portion of the second
audio signal.
[0014] At least one of the first and the second audio signals can
include a surround signal. At least one of the first and the second
audio signals can include a center channel signal. At least one of
the first and the second audio signals can include a front channel
signal. In one configuration, the first audio signal can include a
surround signal and the second audio signal can include a front
channel signal.
[0015] In another aspect, the invention is embodied in a fader
control. The fader control includes a first control region. A gain
of a first audio signal is decreased while a gain of a first mixed
signal is increased in the first control region. The first mixed
signal includes a portion of the first audio signal and a portion
of a second audio signal. A second control region is located
adjacent to the first control region. Again of a third audio signal
is decreased while a gain of a second mixed signal is increased in
the second control region. The second mixed signal includes a
portion of the third audio signal and a portion of a fourth audio
signal.
[0016] An additional third control region can be located between
the first and the second control region. The third control region
provides a pure fading function. A center position of the fader
control can be located between the first and the second control
region. The center position includes a neutral fading position.
[0017] At least one of the first, second, third, and fourth audio
signals can include a surround signal. At least one of the first,
second, third, and fourth audio signals can include a center
channel signal. The first audio signal can include a surround
signal and the second audio signal can include a front channel
signal. The third audio signal can include a center channel signal
and the fourth audio signal can include a surround signal.
[0018] In one aspect, the invention is embodied in a method for
determining a position of a fader control of an audio system. The
method includes calculating a ratio of a front signal to a rear
signal generated by the audio system. The method can also include
adjusting the position of the fader control and calculating a ratio
of a front signal to a rear signal generated by the audio system.
The method can also include generating a fade contour by generating
a model of fader gain relative to the calculated ratio of the front
signal to the rear signal. The method can also include generating a
fade contour by generating a look up table of fader gain relative
to the calculated ratio of the front signal to the rear signal. The
method can also include taking a weighted average of the front
signal and the rear signal generated by the audio system.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0019] Other features, objects and advantages of this invention may
be better understood by referring to the following description in
conjunction with the accompanying drawings, where like reference
symbols indicate like structural elements and features in
which:
[0020] FIG. 1 is a block diagram of a multi-channel discrete
surround sound system in an automotive listening environment.
[0021] FIG. 2 is a rotary control diagram for a single degree of
freedom controller that may be used in a surround sound system.
[0022] FIG. 3 is an illustrative chart of the various input signals
and signal levels applied to each transducer for each position of
the control device shown in FIG. 2.
[0023] FIG. 4 is a representative diagram of a finer resolution
control scheme for the transition region between the surround level
control region and the rear fading control region.
[0024] FIG. 5 shows an illustrative chart of the various input
signals and signal levels applied to each transducer for each
intermediate position of the control device shown in FIG. 4.
[0025] FIG. 6 is a block diagram of spatially diverse transducers
in a multi-channel discrete surround sound system in an automotive
listening environment.
[0026] FIG. 7 illustrates a rotary control diagram for a surround
level control according to one embodiment of the invention.
[0027] FIG. 8 illustrates a rotary control diagram for a fader
control according to one embodiment of the invention.
[0028] FIG. 9 illustrates a rotary control diagram for a fader
control according to another embodiment of the invention.
[0029] FIG. 10 illustrates a graph of a fade contour according to
one embodiment of the invention.
[0030] FIG. 11 illustrates a schematic diagram of a downmix module
according to one embodiment of the invention.
[0031] FIG. 12 illustrates a schematic diagram of a downmix module
according to another embodiment of the invention.
[0032] FIG. 13 is an illustrative signal mixer having signal mixing
coefficients for various channels in a surround sound system
according to the invention.
[0033] FIG. 14 is a signal processor having signal coefficients for
various channels in a surround sound system that can be used with
the downmix module of FIG. 11.
DETAILED DESCRIPTION
[0034] The disclosed system and techniques will be described and
illustrated assuming an automotive listening environment. However,
the techniques may be applicable to other types of listening
environments, such as a living room, theater, and the like.
[0035] FIG. 1 shows a block diagram of a multi-channel discrete
surround sound system in an automotive listening environment. The
surround sound system 150 uses a plurality of discrete surround
sound source signals corresponding to a front left (FL) channel 10,
a front right (FR) channel 20, a center (C) channel 30, a surround
left (SL) channel 40, a surround right (SR) channel 50, and a bass
or Low Frequency Effects (LFE) channel 60. Although six source
signal channels are illustrated and described, the number of source
signal channels may vary. For example, the surround sound system
150 may not include a center channel 30 and/or an LFE channel 60.
Alternatively, the surround sound system 150 may include a surround
center channel (not shown). Thus, the number of source signal
channels may be smaller than six or larger than six.
[0036] The discrete signals 10-60 are received by a signal
processor 70 for operating on the signals 10-60. The signal
processor 70 may be implemented in the form of a digital signal
processor (DSP) or in analog circuitry. The signal processor 70
performs one or more functions on the various input signals 10-60
to create output signals. One function that may be performed by the
signal processor 70 is alteration of signal gain. The signal
processor 70 may either attenuate or boost (in either absolute or
relative terms) one or more of signals 10-60 based on selected
control parameters, as will be described in more detail below.
[0037] Another function that may be performed by the signal
processor 70 is signal mixing. The signals 10-60 may be mixed
together in some fashion within signal processor 70, with variable
relative or absolute gain. Signal mixing takes as input a plurality
of input signals, mixes together one or more subsets of the input
signals, and generates a plurality of output signals. Mixing may
include attenuating or boosting the relative level of the input
signal subsets to be mixed and summing together the adjusted input
signals. Some or all of the output signals may contain components
of multiple (i.e., more than one) input signals. The number of
input signals may differ from the number of output signals. If the
number of output signals is smaller than the number of input
signals, the process is referred to as downmixing. If the number of
output signals is greater than the number of input signals, the
process is referred to as up-mixing.
[0038] The signal processor 70 may perform still other functions on
the various input signals to create the output signals. For
example, the difference between a pair of signals could be taken
and output as a signal. The described techniques are not limited in
the functions that can be performed on the input signals and are
not limited in the number of input signals or output signals that
may be present.
[0039] After the desired functions have been performed, the output
signals from the signal processor 70 may be selectively sent to a
plurality of spatially diverse transducers. The transducers may
include a front left transducer (FL-T) 80, a center transducer
(C-T) 90, a front right transducer (FR-T) 100, a surround left
transducer (SL-T) 110, a low frequency effects transducer (LFE-T)
120, and a surround right transducer (SR-T) 130. The various
transducers 80-130 may be installed in a vehicle 140. Similar to
the number of source signals, the number of transducers can also be
smaller than or larger than six.
[0040] The values of the control parameters that may be used to
adjust the input (source) signals, with or without mixing, may be
selected depending on a variety of factors, such as the location of
the loudspeakers and whether the purpose of the signal processing
is for surround sound level control or image fading control. The
control parameters may also depend on the acoustic characteristics
of the listening environment.
[0041] FIG. 2 shows a rotary control diagram for a single degree of
freedom controller that may be used in a surround sound system. The
described techniques are not restricted to a rotary control device,
however. Other controls such as a slider, or
+/-(increment/decrement control) control set, may also be
implemented. The control device may include some type of
potentiometer for varying an analog signal or control voltage, or
may be some type of encoder that outputs a digital code depending
on position or actuation of the control device. A digital encoder
(which may be rotary, linear, increment/decrement, or some other
type of control device) may be used for digital (DSP)
implementations.
[0042] The control device can be in the form of a remote control or
a controller mounted somewhere in the listening environment. The
control device may also be located on a component of the surround
sound system, such as the control interface unit for a vehicle
audio system. For simplicity, the following description assumes use
of a rotary control device, although the techniques are equally
applicable in connection with other types of control devices.
[0043] As illustrated in FIG. 2, the total control region for the
rotary control device is divided into a plurality of control
regions. In the illustrated implementation, the rotary control
device includes five control regions: a surround level control
region 205 between positions 5 and 11 clockwise, a rear fading
control region 210 between positions 12 and 15 clockwise, a front
fading control region 215 between positions 1 and 4 clockwise, a
first transition region 220 between positions 11 and 12 clockwise,
and a second transition region 225 between positions 4 and 5
clockwise. There are numerous ways to divide the control region,
however, and the described techniques are not limited in the manner
in which the control regions are divided. For example, the surround
sound level control region 205 could be located between positions 4
and 12 clockwise, and front fading and rear fading control regions
210 and 215 could be correspondingly smaller. The control regions
could also be divided up asymmetrically, instead of symmetrically
as shown in FIG. 2. Greater or fewer numbers of tuning steps (a
total of 15 are shown in FIG. 2) may also be used. In some
implementations, the number of tuning steps may be sufficiently
large that the difference between adjacent tuning steps is
virtually imperceptible even when the entire range of tuning steps
produces noticeably different audible results. Furthermore, some
implementations may not include transition regions 220 and 225
and/or may include only one fading control region.
[0044] As an illustrative example, in the surround level control
region 205, each clockwise rotation step may increase the surround
signal level by 1.5 dB. The surround level control region 205 may
simultaneously control a single monophonic surround signal, a
stereo pair of surround signals, or multi-channel surround signal
levels (e.g., left surround, left center surround, right center
surround, and right surround, as might be present in a 7.1 channel
implementation). In the example of FIG. 2, a total level change
(increase) of 9 dB (6*1.5) could be produced by clockwise rotation
of the rotary control device from position 5 to position 11. In one
implementation, position 8 may correspond to a 0 db surround level
adjustment relative to the original input surround signals,
position 11 may correspond to a +4.5 dB adjustment relative to
position 8 (each step, such as from positions 8 to 9, increases the
level by 1.5 dB), and position 5 may correspond to -4.5 dB
adjustment relative to position 8 (each step, such as from
positions 8 to 7, decreases the level by 1.5 dB). The step sizes
described here are used for illustrative purposes and, in actual
implementations, can be varied as desired. Additionally, the level
change with each step change need not be constant. The level change
when moving from position 8 to position 9 may be different from the
level change when moving from position 9 to position 10, and so
on.
[0045] In the rear fading region 210 between position 12 and
position 15, the output level of the front transducers (FL-T 80,
FR-T 100, and C-T 90) with respect to the rear transducers (SL-T
110, SR-T 130, and LFE-T 120) may be adjusted for each tuning step.
This adjustment may be accomplished by operating on the signals
that are applied to the different transducers. A different function
may be performed when the control device is actuated over the rear
fading region 210 portion of the rotary control device's operating
range than is performed in the surround level control region 205
(e.g., over the range from positions 5 to 11). Furthermore, the
rear fading control region 210 may control a different set of
signals (e.g., levels of more than just surround signals may be
adjusted).
[0046] For example, clockwise rotation of the control device in the
rear fading region 210 may cause the signals fed to the rear
transducers to be stronger than the signals fed to the front
transducers (i.e., a rear fade function). In addition, the signals
fed to the rear transducers may have components of the left front,
center, and right front input signals. The signals fed to the front
transducers may also contain information from the surround input
signals. In some implementations, the signals fed to the front
and/or rear transducers may also contain information from the low
frequency effects input signals.
[0047] There are a variety of possible methods to adjust relative
output levels of the front and rear transducers. For each clockwise
step of the rotary control in the rear fading scenario, fading can
be accomplished by: 1) keeping signals fed to the front transducers
unchanged and boosting signals fed to the rear transducers; 2)
attenuating signals fed to the front transducers and keeping
signals fed to the rear transducers unchanged; 3) attenuating
signals fed to the front transducers and boosting signals fed to
the rear transducers.
[0048] In the front fading region 215 between position 1 and
position 4, the output level of the rear transducers (SL-T 110,
SR-T 130, and LFE-T 120) with respect to the front transducers
(FL-T 80, FR-T 100, and C-T 90) may be adjusted for each tuning
step. This adjustment may be accomplished by operating on the
signals that are applied to the different transducers. A different
function may be performed when the control device is actuated over
the front fading region 215 portion of the rotary control device's
operating range than is performed in the surround level control
region 205 (e.g., over the range from positions 5 to 11) and the
rear fading region 210 (e.g., over the range from positions 12 to
15). Furthermore, the front fading control region 215 may control a
different set of signals.
[0049] For example, counterclockwise rotation of the control device
in the front fading region 215 may cause the signals fed to the
front transducers to be stronger than the signals fed to the rear
transducers (i.e., a front fade function). In addition, the signals
fed to the front transducers may have components of the left
surround and right surround input signals. The signals fed to the
rear transducers may also contain information from the front input
signals. In some implementations, the signals fed to the front
and/or rear transducers may also contain information from the low
frequency effects input signals. The combination of signals may be
performed in a different way for operation in the front fading
region 215 as compared to operation in the rear fading region 210.
For example, operation in the rear fading region 210 may result in
signals being fed to the rear transducers that have significant
front transducer components, while operation in the front fading
region 215 may result in signals being fed to the front transducers
that have relatively small surround transducer components.
[0050] There are a variety of possible methods to adjust relative
output levels of the front and rear transducers. For each
counterclockwise step of the rotary control in the front fading
scenario, fading can be accomplished by: 1) keeping signals fed to
the rear transducers unchanged and boosting signals fed to the
front transducers; 2) attenuating signals fed to the rear
transducers and keeping signals fed to the front transducers
unchanged; 3) attenuating signals fed to the rear transducers and
boosting signals fed to the front transducers.
[0051] FIG. 3 shows an illustrative control parameter chart 250 of
the various input signals and signal levels applied to each
transducer for each position of the control device shown in FIG. 2.
The control device may be used for a surround sound application in
a vehicle, for example. The surround signal level fed to selected
transducers is controlled over a first region of operation. Over
other regions, various signals are mixed (summed) together using
varying relative and absolute levels and then fed to selected
transducers. The control parameter chart 250 of FIG. 3 provides the
signal mixing and corresponding control parameter values for a six
transducer surround sound configuration, as shown in FIG. 1, which
uses the rotary control device depicted in FIG. 2. A horizontal
axis 255 of the chart 250 represents the control position 1-15 as
shown in FIG. 2. A vertical axis 260 of the chart 250 represents
the six transducers (FL-T 80, FR-T 100, C-T 90, SL-T 110, SR-T 130,
and LFE-T 120), as shown in FIG. 1. The chart 250 represents one
possible implementation of a surround level and fading control
system. Other signal mixing combinations and parameter values may
be used.
[0052] Each cell in FIG. 3 shows the discrete signals that are
mixed together for each transducer and each control device
position. Each cell also shows control parameters that are to be
applied to the discrete signals for each transducer and each
control device position. The control parameters represent gain
changes relative to the original input signals. For example, for
the front left transducer 80, when the control is set at position 1
(see FIG. 2), the discrete front left and surround left signals (FL
and SL) are processed with particular gain changes, 0 dB and -1.5
dB respectively (as shown in cell 280), and then mixed together
(summed). The mixed signal is fed to the front left transducer 80.
For the left surround transducer 110, when the control device is
set at position 12 (see FIG. 2), discrete front left, center, and
surround left signals (FL, C, and SL) are processed with specific
gain changes, -1.5 dB each (as shown in cell 290), and then mixed
together. The mixed signal is then fed to the left surround
transducer 110. The value of the control parameters may be selected
in accordance with certain criteria that relate to, for example,
optimizing perceived sound quality and/or maintaining a constant
overall system output level.
[0053] For the surround level control region 205 (between positions
5 and 11 clockwise), the surround input signals and the front input
signals are preserved as discrete. That is, no signal mixing takes
place, and only gain changes of surround signals relative to the
other signals are implemented. When the control device is set at
position 8, all of the discrete signals are passed to the
corresponding transducer without any gain change. From position 8,
every clockwise rotation step increases the surround signal level
or levels (SL and SR signals) by a predetermined amount, such as
1.5 dB. At position 9, the left and right surround signals (SL and
SR) will have a gain increase of 1.5 dB (see cells 287-1 and 287-2)
while other discrete signals are passed through without
modifications. Each additional clockwise rotation step results in a
further gain increase for the left and right surround signals. In
this example implementation, both the left and right surround
signals (SL and SR) have a 2 dB gain change when moving from
position 10 to position 11. Thus, signal boosts or attenuations
provided by each control step need not be constant. The values used
in any particular implementation may be selected depending on
expected system and listening environment specifications.
[0054] Similarly, starting from position 8, every counterclockwise
rotation step decreases the left and right surround signal level or
levels (SL and SR signals) by a predetermined amount, such as 1.5
dB. In this example, at position 7, the left and right surround
signals (SL and SR) have a gain change of -1.5 dB (see cells 288-1
and 288-2) and all other signals are passed through without
modification. Additional counterclockwise rotation steps results in
a further gain attenuation for the left and right surround
signals.
[0055] In the rear fading control region 210 (between positions 12
and 15 clockwise), the audio image is faded to the rear with each
clockwise step rotation. For operation in this range, the audio
signals passed through the signal processing associated with the
control device are no longer maintained as discrete. For example,
the audio does not represent discrete multi-channel surround sound,
but instead input signals are mixed in some manner. However, all of
the surround sound information is still present.
[0056] From position 12 (see FIG. 2), every clockwise step rotation
makes signals fed to the rear transducers 110 and 130 (SL-T and
SR-T) relatively stronger than signals fed to the front transducers
80, 90, and 100 (FL-T, FR-T and C-T). Although a particular
implementation is illustrated, there are a variety of possible
implementations for adjusting relative signal strength between the
front transducers and the rear transducers such as: 1) keeping
signals fed to the front transducers unchanged and boosting signals
fed to the rear transducers; 2) attenuating signals fed to the
front transducers and keeping signals fed to the rear transducers
unchanged; 3) attenuating signals fed to the front transducers and
boosting signals fed to the rear transducers. Any of these methods,
alone or in combination, may be used to effect a fade function. The
illustrated example keeps the strength of the signals fed to the
rear transducers unchanged and decreases the strength of the
signals fed to the front transducers, for clockwise step rotations
in the region from positions 12 to 15.
[0057] In this example, at position 13, the discrete front left
signal (FL) is adjusted by being attenuated by 8 dB, the discrete
surround left signal (SL) is adjusted by being attenuated by 10 dB,
and the two adjusted signals are mixed and fed to the front left
transducer 80 (FL-T) (as shown at cell 295-1). In another
implementation, the front left and surround left signals (FL and
SL) may be attenuated by the same magnitude, such as 8 dB. In such
a case, the signals could be mixed together before being
attenuated, rather than after. In other words, if the front left
and surround left signals (FL and SL) are attenuated by the same
magnitude (e.g., 8 dB), the implementation can feed the front left
and surround left signals (FL and SL) to the front left transducer
(FL-T) without any pre-adjustment. Instead, the output of the front
left transducer 80 may be adjusted to achieve the same 8 dB
attenuation on both signals FL and SL. Thus, the signal adjustments
for a mixing signal scenario can be performed either in the signal
processor or in the transducers to which the signals are fed if the
adjustment amounts for all the mixed signals are the same.
Similarly, the signal adjustments for a discrete signal scenario
(such as for the signal fed to the center transducer 90 (C-T)) can
be performed either in the signal processor or in the transducers
to which the signal is fed.
[0058] Different adjustments and mixing are performed at position
13 for the surround transducers as compared to the front
transducers. For example, the discrete front left signal (FL) is
adjusted by being attenuated by 1.5 dB, discrete center signal (C)
is adjusted by being attenuated by 1.5 dB, discrete surround left
signal (SL) is adjusted by being attenuated by 1.5 dB, and the
three adjusted signals are mixed and fed to the left surround
transducer 110 (SL-T) (as shown at cell 295-2).
[0059] At position 15, all signals fed to the front transducers 80,
90, and 100 (FL-T, FR-T and C-T) are adjusted to be attenuated by
60 dB (as shown in cells 295-3, 295-4, and 295-5). In this case,
virtually no sound can be heard coming from front transducers. The
signals fed to the rear transducers 110 and 130 (SL-T and SR-T), on
the other hand, are set back to their original levels and combined
with unadjusted front signals (as shown in cells 295-6 and
295-7).
[0060] In the front fading control region (between positions 1 and
4 clockwise), the audio image is faded to the front with each
counterclockwise step rotation. For operation in this range, the
audio signals that pass through the signal processing associated
with the control device are not maintained as discrete. For
example, the audio is not discrete multi-channel surround sound,
but instead uses input signals that are mixed in some manner.
However, all of the surround sound information is still
present.
[0061] From position 4, every counterclockwise step rotation makes
signals fed to the front transducers 80, 90, and 100 (FL-T, FR-T
and C-T) relatively stronger than signals fed to the rear
transducers 110 and 130 (SL-T and SR-T). In this example, the
strength of the front signals (FL and FR) fed to the front
transducers remains unchanged while the strength of the surround
signals (SL and SR) fed to the front transducers generally
increases with each counterclockwise step rotation. At the same
time, the strength of the signals fed to the rear transducers is
decreased for counterclockwise step rotations in the region from
position 4 to 1. However, there are a variety of possible
implementations for adjusting relative signal strength between the
front transducers and the rear transducers such as: 1) keeping
signals fed to the rear transducers unchanged and boosting signals
fed to the front transducers; 2) attenuating signals fed to the
rear transducers and keeping signals fed to the front transducers
unchanged; 3) attenuating signals fed to the rear transducers and
boosting signals fed to the front transducers. Any of the methods,
alone or in combination, may be used to effect a fade function.
[0062] As a specific example of the front fading control region, at
position 3, a discrete front left signal (FL) passes through
without any adjustment (having 0 dB control parameter), discrete
surround left signal (SL) is adjusted by being attenuated by 3 dB,
and the two adjusted signals are mixed and fed to the front left
transducer 80 (FL-T) (as shown in cell 285-1). In another
implementation, the front left and surround signals FL and SL could
be attenuated by the same magnitude, such as 3 dB. In this case,
the signals could be mixed together before being attenuated, rather
than after. Also at position 3, the discrete front left signal (FL)
is adjusted by being attenuated by 9 dB, the discrete surround left
signal (SL) is adjusted by being attenuated by 13 dB, and the
adjusted signals are mixed and fed to the left surround transducer
110 (SL-T) (as shown in cell 285-2).
[0063] At position 1, all signals fed to the rear transducers 110
and 130 (SL-T and SR-T) are adjusted to be attenuated by 60 dB (as
shown in cell 285-3 and 285-4). In this situation, virtually no
sound can be heard coming from the rear transducers.
[0064] The transition region between the surround level control
region and the rear fading control region (between positions 11 and
12 clockwise in FIG. 2) serves as a transition region between the
surround signal level and rear fade control functions. Similarly,
the transition region between the surround level control region and
the front fading control region (between positions 5 and 4
counterclockwise in FIG. 2) serves as a transition region between
the surround signal level and front fade control functions. These
transition regions may be used to make the transition between
control functions as smooth as possible. This smoothing can be
accomplished by keeping the system output level approximately
constant when switching between surround level control and fading
functions and by making the transition between non-mixed and mixed
signals as continuous as possible.
[0065] FIG. 4 shows a representative diagram of a finer resolution
control scheme 300 for the transition region between the surround
level control region and the rear fading control region. A similar
control scheme may be used for the transition region between the
surround level control region and the front fading control region.
The finer resolution control scheme 300 includes a plurality of
intermediate control positions 1', 2', . . . , and 3'. Each
intermediate control position may represent an intermediate level
of mixing and an intermediate system output level with respect to
positions 11 and 12.
[0066] FIG. 5 shows an illustrative control parameter chart 500 of
the various input signals and signal levels applied to each
transducer for each intermediate position of the control device
shown in FIG. 4. The chart represents an example of signal mixing
and corresponding gain control parameters values for the transition
region between positions 11 and 12. For simplicity, it is assumed
that there are three finer intermediate steps between positions 11
and 12, although other numbers of intermediate control positions
may be used. A horizontal axis 505 of the chart 500 represents the
intermediate control positions 1'-3' as shown in FIG. 4. A vertical
axis 510 of the chart 500 represents the six transducers (FL-T 80,
FR-T 100, C-T 90, SL-T 110, SR-T 130, and LFE-T 120) as shown in
FIG. 1. The chart 500 represents one possible implementation of a
transition region for a surround level and fading control system.
Other signal mixing combinations and parameter values may be
used.
[0067] For the front transducers, clockwise step rotations result
in an attenuation of the discrete front left, front right, and
center signals (FL, FR and C). Surround left and surround right
signals (SL and SR) are added to front left and front right signals
(FL and FR), respectively, and are boosted at each rotation step.
For the rear transducers, the discrete front left and front right
signals (FL and FR) are added to the surround left and surround
right signals (SL and SR), respectively. In addition, the center
signal (C) is added equally to the surround left and surround right
signals (SL and SR). The front left, front right, and center
signals (FL, FR, and C) are boosted at each rotation step and
discrete surround left and surround right signals (SL and SR) are
attenuated each step.
[0068] For the left front transducer 80 (FL-T), when transitioning
from position 11 to 12, the discrete front left signal (FL) will be
gradually attenuated from 0 dB at position 11 (as shown at cell
600-1) to -4 dB at position 12 (as shown at cell 600-2). The
surround left signal (SL) is gradually mixed in with the discrete
front left signal (FL) initially with -60 dB of relative gain (so
that it is barely audible) at position 1', and the surround left
signal gain is increased with each clockwise step rotation to reach
-6 dB at position 12.
[0069] For the left surround transducer 110 (SL-T), when
transitioning from position 11 to 12 in a clockwise direction, the
surround left signal (SL) may be gradually attenuated from 5 dB
relative gain at position 11 (as shown at cell 610-1) to -1.5 dB
gain at position 12. As the transition is made, front left and
center signals (FL and C) are gradually mixed in with the discrete
surround left signal (SL). Specifically, discrete front left and
center signals (FL and C) are gradually mixed in starting with -60
dB relative gain at position 1', and gains for the front left and
center signals (FL and C) are increased with each clockwise step
rotation to -1.5 dB at position 12 (as shown at cell 610-2). Other
possible implementations of the transition region are possible. For
example, other parameter values may be used and alternative mixing
methods may be used.
[0070] The second transition region between surround level control
and forward fading control may use a transition method similar to
that shown in FIG. 5.
[0071] FIG. 6 is a block diagram of spatially diverse transducers
in a multi-channel discrete surround sound system 620 in an
automotive listening environment. The surround sound system uses a
plurality of discrete surround sound source signals corresponding
to a front left (FL) channel 622, a front right (FR) channel 624, a
front center (FC) channel 626, a surround left (SL) channel 628, a
surround right (SR) channel 630, and a back center (BC) channel
632. Although six source signal channels are illustrated and
described, the number of source signal channels may vary. For
example, the surround sound system 620 can also include a
low-frequency effects (LFE) channel. Thus, the multi-channel
discrete surround sound system 620 can be a 5.1, 6.1, 7.1 or an 8.1
discrete surround system, for example.
[0072] The discrete signals 622-632 are received by a signal
processor 634 for operating on the signals 622-632. The signal
processor 634 may be implemented in the form of a digital signal
processor (DSP) or in analog circuitry. The signal processor 634
performs one or more functions on the various input signals 622-632
to create output signals. One function that may be performed by the
signal processor 634 is alteration of signal gain. The signal
processor 634 can either attenuate or boost (in either absolute or
relative terms) one or more of signals 622-632 based on selected
control parameters, as will be described in more detail below.
[0073] Another function that can be performed by the signal
processor 634 is signal mixing. The signals 622-632 can be mixed
together in some fashion within signal processor 634, with variable
relative or absolute gain. Mixing can include adjusting via
attenuating or boosting the relative or absolute level of the input
signal subsets to be mixed and summing together the adjusted input
signals. One or all of the output signals can contain components of
multiple (i.e., more than one) input signals. The number of input
signals 622-632 can differ from the number of output signals.
[0074] The signal processor 634 can perform still other functions
on the various input signals 622-632 to create the output signals.
For example, the difference between a pair of signals could be
taken and output as a signal. The described techniques are not
limited in the functions (e.g., mixing) that can be performed on
the input signals and are not limited in the number of input
signals or output signals that can be present.
[0075] After the desired functions have been performed, the output
signals from the signal processor 634 can be selectively sent to a
plurality of spatially diverse transducers. The transducers can
include a front left transducer (FL-T) 636, a front center
transducer (FC-T) 638, a front right transducer (FR-T) 640, a
surround left transducer (SL-T) 642, a back center transducer
(BC-T) 644, and a surround right transducer (SR-T) 646. The various
transducers 636-646 can be installed in a vehicle 648. Similar to
the number of source signals, the number of transducers can also be
smaller than or larger than six.
[0076] The values of control parameters that can be used to adjust
the input (source) signals, with or without mixing, may be selected
depending on a variety of factors, such as the location of the
transducers and whether the signal processor 634 performs signal
mixing, surround sound level control, image fading control, or a
combination of signal processing. The control parameters may also
depend on the acoustic characteristics of the listening
environment, such as the type of upholstery in the vehicle, number
of seats, number of passengers, headliner material, interior
volume, etc.
[0077] In some embodiments, a separate fader control and surround
level control can be used to control the input signals 622-632. For
example, the fader control and/or the surround level control can
each include a single degree of freedom rotary controller. The
controller is not restricted to a rotary control device, however.
Other controls such as a slider, or +/- (increment/decrement
control) control set, can also be implemented. The control can
include a potentiometer for varying an analog signal or control
voltage, or can be an encoder that outputs a digital code depending
on position or actuation of the control device. A digital encoder
(which may be rotary, linear, increment/decrement or some other
type of control device) can be used for digital (DSP)
implementations.
[0078] The control device can be in the form of a remote control or
a controller mounted somewhere in the listening environment. The
control device may also be located on a component of the surround
sound system, such as the control interface unit for a vehicle
audio system. For simplicity, the following description assumes use
of a rotary control device, although the techniques are equally
applicable in connection with other types of control devices. In
one embodiment, the level (gain) of the surround signals that are
mixed can be controlled by a separate surround level control
described with reference to FIG. 7. For example, the surround
signal level control can increase or decrease the gain of the rear
surround signals that are applied to the rear transducers 642, 644,
646 of FIG. 6.
[0079] In addition, the surround signal level control can increase
or decrease the gain of the rear surround signals that are mixed
with the front signals during the front fading operation. This can
affect the gain of the portion of the rear surround signals that
are mixed with the front signals and therefore change the gain
ratio of the rear surround signals to the front signals. For
example, the surround signal level control can increase the gain of
the surround signals that are mixed with the front signals so that
the surround signals are more prominent in the signal mix.
Alternatively, the surround signal level control can decrease the
gain of the surround signals that are mixed with the front signals
so that the surround signals are less prominent in the signal mix.
In one embodiment, the gain of the surround signals is
predetermined to keep the sound energy constant in the vehicle.
[0080] In order to retain front center channel information when
fading backward, at least a portion of the front center channel
signal can be mixed with the rear surround signals in the rear
fading region. The percentage of the front center channel signal
that is mixed with the rear surround signals can remain constant or
can change as the fader control gradually fades backward. Mixing
parameters can be controlled by the degree of backward fading and
the front center channel signal level. For example, the percentage
of the front center channel signal that is mixed with the rear
surround signals increases as the fader control gradually fades
backward to position. The level (gain) of the front center channel
signal that is mixed can be controlled by a separate center channel
level control (not shown), or by a portion of the surround level
control described with reference to FIG. 7. For example, a portion
of the surround signal level control can control the gain of the
front center channel signal. The portion of the surround signal
level control can increase or decrease the gain of the front center
channel signal that is applied to the front center channel
transducer 638 of FIG. 6.
[0081] It should be noted that front left and/or front right
channel information could be directly retained when fading backward
by mixing at least a portion of the front left and/or front right
channel information with the rear surround signals in the rear
fading region. In one embodiment, the front center channel
information includes the front left and/or front right channel
information. Thus, retaining the center channel information also
retains the front left and/or front right channel information.
[0082] FIG. 7 illustrates a rotary control diagram for a surround
level control 650 according to one embodiment of the invention. The
surround level control 650 is shown as a rotary controller,
however, other controls such as a slider, or
+/-(increment/decrement control) control set, can also be
implemented. The surround level control 650 can include a
potentiometer for varying an analog signal or control voltage, or
can be an encoder that outputs a digital code depending on position
or actuation of the surround level control 650. A digital encoder
(which may be rotary, linear, increment/decrement, or some other
type of control device) may be used for digital (DSP)
implementations. The surround level control 650 can be in the form
of a remote control or a controller mounted somewhere in the
listening environment. The surround level control 650 can also be
located on a component of the surround sound system, such as the
control interface unit for a vehicle audio system.
[0083] The surround level control can control the gain of the
surround sound signals. For example, each clockwise rotation step
can increase the surround signal level by 1.5 dB. The surround
level control 650 can simultaneously control a single monophonic
surround signal, a stereo pair of surround signals, or
multi-channel surround signal levels (e.g., left surround, left
center surround, right center surround, and right surround, as
might be present in a 7.1 channel implementation).
[0084] In the example of FIG. 7, a total level change of 21 dB
(14*1.5) could be produced by clockwise rotation of the rotary
control device from position one 652 to position fifteen 654. In
one implementation, position eight 655 can correspond to a 0.0 dB
surround level adjustment relative to the original input surround
signals, position fifteen 654 can correspond to a +10.5 dB
adjustment relative to position eight 655 (each step, such as from
positions eight 655 to position nine 656, increases the level by
1.5 dB), and position one 652 can correspond to -10.5 dB adjustment
relative to position eight 655 (each step, such as from positions
eight 655 to position seven 657, decreases the level by 1.5 dB).
The step sizes described here are used for illustrative purposes
and, in actual implementations, can be varied as desired.
Additionally, the level change with each step change need not be
constant. The level change when moving from position eight 655 to
position nine 656 can be different from the level change when
moving from position nine 656 to position ten 658, and so on.
[0085] FIG. 8 illustrates a rotary control diagram for a fader
control 660 according to one embodiment of the invention. The fader
control 660 includes a front fading region 662 and a rear fading
region 664. The fader control 660 can also include a center
position 666 which corresponds to a nonfaded position or a neutral
fading position. In one embodiment, the front fading region 662
also includes surround sound mixing for downmixing one or more
surround sound signals with front audio signals, such as the front
left (FL) channel 622, the front right (FR) channel 624, and/or the
front center (FC) channel 626 of FIG. 6. The surround sound signals
can be mixed with the front audio signals as the fader control 660
is rotated counterclockwise from the center position 666. In one
embodiment, the rear fading region 654 also includes center channel
mixing for downmixing a center channel signal with rear surround
sound signals. The center channel signal can be mixed with the rear
surround sound signals as the fader control 660 is rotated
clockwise from the center position 666.
[0086] Although the fader control 660 is shown having two symmetric
regions, the front fading region 662 and the rear fading region
664, there are numerous ways in which to divide the regions. For
example, the front fading region 662 can be larger than the rear
fading region 664 or the rear fading region 664 can be larger than
the front fading region 662. Also, although a total of fifteen
tuning steps are shown, a greater or a fewer numbers of tuning
steps can be used.
[0087] In one embodiment, the fader control 660 operates as
follows. In the rear fading region 654 between position eight and
position fifteen, the output level of the front transducers (FL-T
636, FR-T 640, FC-T 638 of FIG. 6) with respect to the rear
transducers (SL-T 642, SR-T 646, BC-T 644 of FIG. 6) can be
adjusted for each tuning step. This adjustment can be accomplished
by operating on the signals that are applied to the different
transducers. For example, a mixing function can be performed when
the fader control 660 is actuated over the rear fading region 664
portion of the rotary controller's operating range to downmix
center channel information into the rear transducers. Furthermore,
the rear fading region 664 can mix and/or control a different set
of signals (e.g., mixing of more than just center channel
information into the surround signals can be performed).
[0088] For example, clockwise rotation of the fader control 660 in
the rear fading region 664 can cause the signals fed to the rear
transducers 642, 644, 646 to be stronger than the signals fed to
the front transducers 636, 638, 640 (i.e., a rear fade function).
In addition, the signals fed to the rear transducers 642, 644, 646
can have components of one or more of the front left 622, front
center 626, and front right 624 input signals. The signals fed to
the front transducers 636, 638, 640 may also contain information
from the surround input signals 628, 630. In some embodiments, the
signals fed to the front and/or rear transducers can also contain
information from low frequency effects input signals (not
shown).
[0089] There are a variety of techniques to adjust relative output
levels of the front 636, 638, 640 and rear transducers 642, 644,
646. For a clockwise rotation of the fader control 660 in the rear
fading region 664, fading can be accomplished by keeping signals
fed to the front transducers 636, 638, 640 unchanged and boosting
signals fed to the rear transducers 642, 644, 646; attenuating
signals fed to the front transducers 636, 638, 640 and keeping
signals fed to the rear transducers 642, 644, 646 unchanged;
boosting signals fed to the front transducers 636, 638, 640 and
attenuating signals fed to the rear transducers 642, 644, 646; or
attenuating signals fed to the front transducers 636, 638, 640 and
boosting signals fed to the rear transducers 642, 644, 646.
[0090] In the front fading region 662 between position one and
position eight, the output level of the rear transducers (SL-T 642,
SR-T 646, and BC-T 644) with respect to the front transducers (FL-T
636, FR-T 640, and FC-T 638) can be adjusted for each tuning step.
This adjustment may be accomplished by operating on the signals
that are applied to the different transducers. For example, a
mixing function can be performed when the fader control 660 is
actuated over the front fading region 662 portion of the operating
range of the fader control 660 to downmix surround sound signal
information into the front transducers 636, 638, 640. Furthermore,
the front fading region 662 can mix and/or control a different set
of signals (e.g., mixing of more than just surround sound signal
information into the front audio signals can be performed).
[0091] For example, counterclockwise rotation of the fader control
660 in the front fading region 662 can cause the signals fed to the
front transducers 636, 638, 640 to be stronger than the signals fed
to the rear transducers 642, 644, 646 (i.e., a front fade
function). In addition, the signals fed to the front transducers
636, 638, 640 can have components of the left surround 628 and
right surround input signals 630. The signals fed to the rear
transducers 642, 644, 646 can also contain information from the
front input signals 622, 624, 626. In some implementations, the
signals fed to the front and/or rear transducers may also contain
information from the low frequency effects input signal, if
present.
[0092] The combination of signals can be mixed and/or controlled in
a different way for operation in the front fading region 662 as
compared to operation in the rear fading region 664. For example,
operation in the rear fading region 664 can result in signals being
fed to the rear transducers 642, 644, 646 that have significant
front signal components, while operation in the front fading region
662 can result in signals being fed to the front transducers 636,
638, 640 that have relatively small surround sound signal
components.
[0093] There are a variety of possible methods to adjust relative
output levels of the front 636, 638, 640 and rear transducers 642,
644, 646. For counterclockwise rotations of the fader control 660
in the front fading region 662, fading can be accomplished by
keeping signals fed to the rear transducers 642, 644, 646 unchanged
and boosting signals fed to the front transducers 636, 638, 640;
attenuating signals fed to the rear transducers 642, 644, 646 and
keeping signals fed to the front transducers 636, 638, 640
unchanged; or attenuating signals fed to the rear transducers 642,
644, 646 and boosting signals fed to the front transducers 636,
638, 640.
[0094] FIG. 9 illustrates a rotary control diagram for a fader
control 670 according to another embodiment of the invention. The
fader control 670 of FIG. 9 is similar to the fader control 650 of
FIG. 8 and includes a front fading region 672 and a rear fading
region 674. The fader control 670 also includes an additional pure
fading region 676. The pure fading region 676 is configured to
include a pure fading function in the middle range of the fader
control 670. By "pure fading function," we mean that no signal
mixing is performed in the pure fading region 676. In one
embodiment, the pure fading region 676 comprises approximately
thirty percent of the full range of the fader control 670. However,
the pure fading region 676 can comprise a larger or smaller
percentage of the full range of the fader control 670.
Additionally, the center position 678 can correspond to a nonfaded
position. The front fading region 672 and the rear fading region
674 can be configured as previously described with reference to the
front fading region 662 and the rear fading region 664 of FIG.
8.
[0095] In one embodiment, the sound energy can be kept constant in
the pure fading region 676, as well as in the front 672 and the
rear fading regions 674. As previously described, the pure fading
region 676 is a region that performs pure fading without
downmixing. The front 672 and the rear fading regions 674 augment
the fade control with downmixing to preserve selected signal
contents. It should be noted that the invention can be implemented
with additional control regions including a fade control that is
augmented with downmixing to preserve selected signal contents as
shown in FIG. 8. Additionally, it should be noted that the fader
control 660 of FIG. 8 and fader control 670 of FIG. 9 can be used
with the surround level control 650 of FIG. 7 to provide
independent adjustment of the surround signal level.
[0096] The regions can be divided in numerous ways. Each region can
introduce various signal gain depending on the position of the
fader control 670. Additionally, the type and degree of signal
mixing can also be made to depend on the position of the fader
control 670. Other signal effects such as phase delays and/or
equalization can also be applied that correspond to the position of
the fader control 670. In one embodiment, the fading regions are
defined in terms of gain only.
[0097] FIG. 10 illustrates a graph 680 of a fade contour according
to one embodiment of the invention. The graph 680 can correspond to
the fader control 650 of FIG. 8 or the fader control 670 of FIG. 9.
In the example using the fader control 670 of FIG. 9, the center
position 678 is shown at position eight. The pure fading region 676
is between about position 6.0 and about position 10.0. At position
6.0, the gain of the front audio signals is increased by about 1.5
dB, while the gain of the rear surround audio signals is decreased
by about 2.5 dB. At position 10.0, the gain of the rear surround
audio signals is increased by about 1.5 dB, while the gain of the
front audio signals is decreased by about 2.5 dB.
[0098] In the front fading region 672, the gain of the front audio
signals is gradually increased to about 3.0 dB at position 1.0,
while the gain of the rear surround audio signals is initially
decreased in a gradual manner and then rapidly decreased to about
-28 dB at position 1.0. In the rear fading region 674, the gain of
the rear audio signals is gradually increased to about 3.0 dB at
position 15.0, while the gain of the front surround audio signals
is initially decreased in a gradual manner and then rapidly
decreased to about -33 dB at position 15.0.
[0099] In order to retain rear surround information when fading
forward, at least a portion of the rear surround signals can be
mixed with the front signals in the front fading region 672. Mixing
parameters can be controlled by the degree of forward fading and
the surround signal level. For example, the amount of the rear
surround signals that are mixed with the front signals increases as
the fader control 670 gradually fades forward to position 1.0.
[0100] In one embodiment, the position of the fader control 670 can
be determined by calculating the ratio of the gains from the front
and rear signals. For example, the ratio of the front left signal
to the rear left signal is equivalent to the ratio of the front
right signal to the rear right signal, assuming a stereo
configuration. Thus, the ratio x (assuming fade to rear) can be
expressed as follows: 1 x = front rear
[0101] The calculation can occur at any rate including lower
(decimated) sample rates. Additionally, any indicator of signal
strength can be used in the calculation of the ratio, such as
root-mean-square (RMS) signal level. RMS can minimize errors due to
time variations and minor signal glitches, for example. Also, left
and right signals can be summed in order to negate the effect of
balance on the signal levels.
[0102] The fade contour 680 can be generated by using the ratio x
for each position of the fader control 670. The fade contour 680 is
a graph of fader gain relative to the position of the fader
control. A polynomial can be used to approximate the fade contour.
The polynomial can be expressed as follows:
Fade Contour=P.sub.0+P.sub.1x+P.sub.2x+ . . . +P.sub.Nx.sup.N
[0103] The coefficients of the polynomial can be calculated using a
model, such as a "least squares fit" model, for example. The order
of the polynomial is determined based on the desired precision of
the fit. For example, a third-order or higher-order polynomial can
be used. In one embodiment, a lookup table that contains the signal
ratio to fader gain information could also be implemented to
generate the fade contour.
[0104] The determination of the position of the fader control can
be used by an amplifier (having a processor) that is coupled to a
head unit through the pre-amplifier outputs of the head unit. By
knowing the position of the fader control, the amplifier can
process signals from the head unit to improve system performance,
such as adjustments of equalization parameters, while maintaining
the fader position desired by the user.
[0105] In one configuration, the amplifier can also recover an
approximation of the 20 original stereo signal as follows. The
original stereo signal can be approximated by taking a weighted
average of the faded signals from the head unit of the audio
system.
Left(t)=a.times.front.times.Left(t)+a.times.rear.times.Left(t)
Right(t)=a.times.front.times.Right(t)+a.times.rear.times.Right(t)
[0106] The ratio x can be expressed as follows (assuming fade to
front): 2 x = rear front
[0107] Solving for a results in the following equation: 3 1 = a
.times. front + a .times. rear = a .times. ( 1 + x ) .times.
front
[0108] In many applications, the front has unity gain when the fade
control fades the signals forward. In other words, the gain in the
direction that is opposite to the direction of the fade is affected
by the fade control. For example, front has unity gain and rear has
attenuated gain when faded forward; conversely, rear has unity gain
when faded rearward and front has attenuated gain. Under this
assumption, the scaling coefficient a can be expressed as follows:
4 a = 1 1 + x
[0109] The weighting function a(x) can be generated by using the
ratio x for each position of the fader control 670. A polynomial
can be used to approximate the weighting function. The polynomial
can be expressed as follows:
a(x)=P.sub.0+P.sub.1x+P.sub.2x.sup.2+ . . . +P.sub.Nx.sup.N
[0110] The coefficients of the polynomial can be calculated using a
model, such as a "least squares fit" model, for example. The order
of the polynomial is determined based on the desired precision of
the fit. For example, a third-order or higher-order polynomial can
be used. In one embodiment, a lookup table that contains the signal
ratio to fader gain information could also be implemented to
generate the fade contour. The value of a can be thus be
determined. The original stereo signal can then be approximated by
substituting the value of a in the previously described
equations.
[0111] FIG. 11 illustrates a schematic diagram of a downmix module
700 according to one embodiment of the invention. The downmix
module 700 operates on surround sound system, such as a 5.1, 6.1,
or 7.1 surround sound configuration. As previously discussed, it is
possible to drop signal information in the extreme fade positions
if deliberate preservation of specific signal contents, such as via
downmixing as shown in FIG. 11, is not taken into consideration.
For example, in a typical surround sound system, the surround
signals will be lost if the audio is faded completely forward. The
downmix module 700 is shown in a schematic diagram to better
illustrate its operation. There are numerous analog and digital
circuit designs that can be used to implement the downmix module
700.
[0112] The present invention provides a technique to preserve
signal information, such as surround channels or a center channel
when performing fading control in a listening environment such as
in a vehicle cabin or listening room. For example, in a typical
surround application with spatially diverse transducers, such as is
shown in FIG. 6, certain signals can be preserved when fading
forward and backward. In some configurations, such as for
facilitating tuning or a specific design, specific signals can
always be present by design. For example, the stereo pair L' and R'
can be configured to always be present in both the front fading
region 672 and the rear fading region 674 of FIG. 9.
[0113] Thus, the surround channels and the center channel content
can be preserved by mixing at least a portion of each of the
surround channels or at least a portion of the center channels into
L' and R'. The downmix module 700 illustrated in FIG. 11 can
include a gain cell for each channel to facilitate independent
content scaling (i.e. signal level control).
[0114] The outputs of the downmix module 700 can be mathematically
described as follows:
L'=(scale.sub.LR.multidot.FL)+(down.sub.LsRs.multidot.L.sub.s')+(down.sub.-
C.multidot.C')
R'=(scale.sub.LR.multidot.FR)+(down.sub.LsRs.multidot.R.sub.s')+(down.sub.-
C'C')
C'=scale.sub.C.multidot.FC
L.sub.s'=scale.sub.LsRs.multidot.SL
R.sub.s'=scale.sub.LsRs.multidot.SR
[0115] where L' 702 is the output of the front left channel of the
downmix module 700, R' 704 is the output of the front right channel
of the downrmix module 700, C' 706 is the output of the front
center channel of the downmix module 700, L.sub.s' 708 is the
output of the left surround channel of the downmix module 700, and
R.sub.s' 710 is the output of the right surround channel of the
downmix module 700.
[0116] In one example, the output of the front left channel (L'
702) is a downmixed signal that includes the product of the front
left signal (FL 712) and a scale factor or coefficient
(scale.sub.LR 714) summed with the product of the output of the
front center channel (C' 706) and a coefficient (down.sub.C 716)
summed with the product of the output of the left surround channel
(L.sub.s' 708) and a coefficient (down.sub.LsRs 718). Thus, the
downmix module 700 mixes the left surround channel (L.sub.s' 708)
with the front left channel (FL 712) to preserve the left surround
information during a front fade operation. The proportions of the
signals that are mixed are determined by the coefficients
scale.sub.LR 714, down.sub.C 716, and down.sub.LsRs 718.
[0117] There are numerous methods of determining the coefficients
(i.e., scale.sub.LR, down.sub.C, down.sub.LsRs) depending on
specific design objects, such as optimizing the perceived sound
effects, keeping sound energy constant, or controlling the amount
of signal mix, for example.
[0118] FIG. 12 illustrates a schematic diagram of a downmix module
750 according to another embodiment of the invention. The downmix
module 750 is similar to the downmix module 700 of FIG. 11 with the
addition of a back center channel 752. Other downmix modules can
also be used. As previously discussed, signal information can be
lost in the extreme fade positions if deliberate preservation of
specific signal contents is not taken into consideration. The
downmix module 750 is shown in a schematic diagram to better
illustrate its operation. There are numerous analog and digital
circuit designs that can be used to implement the downmix module
750.
[0119] The downmix module 750 illustrated in FIG. 12 includes a
gain cell for each channel to facilitate independent content
scaling (i.e. signal level control). The outputs of the downmix
module 750 can be mathematically described as follows:
L'=(scale.sub.LR.multidot.FL)+(down.sub.LsRs.multidot.L.sub.s')+(down.sub.-
C.multidot.C')+(down.sub.BC.multidot.BC')
R'=(scale.sub.LR.multidot.FR)+(down.sub.LsRs.multidot.R.sub.s')+(down.sub.-
C.multidot.C')+(down.sub.BC.multidot.BC')
C'=scale.sub.C.multidot.FC
L.sub.s'=(scale.sub.LsRs.multidot.SL)+(down.sub.BC.multidot.BC')
R.sub.s'=(scale.sub.LsRs.multidot.SR)+(down.sub.BC.multidot.BC')
BC'=scale.sub.BC.multidot.BC
[0120] where L' 754 is the output of the front left channel of the
downmix module 750, R' 756 is the output of the front right channel
of the downmix module 750, C' 706 is the output of the front center
channel of the downmix module 750, L.sub.s' 760 is the output of
the left surround channel of the downmix module 750, R.sub.s' 762
is the output of the right surround channel of the downmix module
750, and BC' 764 is the output of the back center channel of the
downmix module 750.
[0121] In one example, the output of the front left channel (L'
754) is a downmixed signal that includes the product of the front
left signal (FL 712) and the coefficient (scale.sub.LR 714) summed
with the product of the output of the front center channel (C' 706)
and the coefficient (down.sub.C 716) summed with the product of the
output of the left surround channel (L.sub.s' 760) and a
coefficient (down.sub.LsRs 766) summed with the product of the
output of the back center channel (BC' 764) and a coefficient
(down.sub.BC 768). Thus, the downmix module 700 mixes the left
surround channel (L.sub.s' 760) and the back center channel (BC'
764) with the front left channel (FL 712) to preserve the left
surround information during a front fade operation. The proportions
of the signals are determined by the coefficients scale.sub.LR 714,
down.sub.C 716, down.sub.BC 768 and down.sub.LsRs 766.
[0122] In addition to the downmix module 750, a signal mixer can
also be used to further control signal content and signal gain
level. A two-module design includes an additional degree of freedom
from the interaction of the downmix module 750 and the signal mixer
for controlling the signal levels of the various signals. For
example, when fading forward, the overall gain of the signals at
the front left 636 (FIG. 6) and the front right transducers 640
(FIG. 6) can be modified independently by coefficients in the
downmix module 750 and coefficients in the signal mixer.
[0123] FIG. 13 is an illustrative signal mixer 800 having signal
mixing coefficients for various channels in a surround sound system
according to the invention. The signal mixer 800 of FIG. 13 is
illustrated in a table format. In one embodiment, the signal mixer
800 is positioned after the downmix module 700 of FIG. 11. However,
it should be noted that the signal mixer could be positioned before
the downmix module 700 or can be integrated with the downmix module
700 in a single module implementation. The signal mixer 800 is
shown in a table format to better illustrate its operation. There
are numerous analog and digital circuit designs that can be used to
implement the signal mixer 800.
[0124] The signal mixer 800 includes columns corresponding to the
output of the front left channel L' 702, the output of the front
right channel R' 704, the output of the front center channel C'
706, the output of the left surround channel L.sub.s' 708, and the
output of the right surround channel R.sub.s' 710 of the downmix
module 700. Each of the columns includes various coefficients that
can be applied to the signals. The fade column 802 includes fader
coefficients (e.g., fading gains) indicated as front 804 and rear
806 that can also be applied to the signals depending on the
particular fading region. The coefficients front 804 and rear 806
can vary with position of the fade control. For example, the
coefficient front 804 can increase and the coefficient rear 806 can
decrease as the fader control is faded forward.
[0125] The signal mixer 800 includes rows corresponding to the
outputs of the signal mixer 800 which will be fed to the various
speakers. The front left output is indicated by FL' 812, the front
right output is indicated by FR' 814, the front center output is
indicated by FC' 816, the surround left output is indicated by SL'
818, and the surround right output is indicated by SR' 820. An
optional back center output is indicated by BC' 822.
[0126] The output for the front left channel (FL' 812) according to
the signal mixer 800 can be represented as follows: 5 FL ' = front
( a L ' + b C ' ) = ( front a L ' ) + ( front b C ' )
[0127] Substituting L' and C' from the downmix module 700 of FIG.
11 yields the following: 6 FL ' = front a ( scale LR FL + down LsRs
Ls ' + down C C ' ) + front b C ' = ( front a scale LR ) FL + (
front a down LsRs scale LsRs ) SL + ( front a down C scale C +
front b scale C ) FC
[0128] Similarly, the output for the front right channel (FR' 814)
according to the signal mixer 800 can be represented as follows: 7
FR ' = front ( a R ' + b C ' ) = ( front a R ' ) + ( front b C '
)
[0129] Substituting R' and C' from the downmix module 700 of FIG.
11 yields the following: 8 FR ' = front a ( scale LR FR + down LsRs
Rs ' + down C C ' ) + front b C ' = ( front a scale LR ) FR + (
front a down LsRs scale LsRs ) SR + ( front a down C scale C +
front b scale C ) FC
[0130] In the pure fading region 676 of FIG. 9, a pure fading
function is applied and the downmix module is effectively bypassed.
This can be achieved by setting the coefficients as follows:
scale.sub.LR=scale.sub.LsRs=scale.noteq.0
down.sub.C=0
down.sub.LsRs=0
[0131] This yields front left (FL' 812) and front right signals
(FR' 814) without deliberately preserving surround content as
follows:
FL'=(front.multidot.a.multidot.scae.sub.LR).multidot.FL+(front.multidot.b.-
multidot.scale.sub.C).multidot.FC
FR'=(front.multidot.a.multidot.scale.sub.LR).multidot.FR+(front.multidot.b-
.multidot.scale.sub.C).multidot.FC
[0132] Thus, in the pure fading region 676, surround signal content
is not deliberately preserved when fading forward. By design of the
signal mixer 800 (FIG. 13), at least a portion of the front center
channel signal content is downmixed with the front left and the
front right signals. However, the center channel signal content can
be dropped by setting the coefficient b to zero. In one embodiment,
the portion of the center channel signal is not downmixed with the
front left and the front right signals as will be described with
reference to FIG. 14.
[0133] In the front fading region 672 of FIG. 9, the signals are
faded and downmixing occurs to preserve surround signal content.
Since front center channel content is generally present in the
forward fade position, the coefficient down.sub.c can be set to
zero. However, the coefficient down.sub.c can be set to non-zero
values if desired. The preservation of the surround signal is
accomplished by setting the coefficient down.sub.LsRs to a non-zero
value. This yields front left (FL' 812) and front right signals
(FR' 814) with preserved surround signal content as follows:
scale.sub.LR=scale.sub.LsRs=scale.sub.C.noteq.0
down.sub.C=0
down.sub.LsRs.noteq.0
FL'=(front.multidot.a.multidot.scale.sub.LR).multidot.FL+(front.multidot.a-
.multidot.down.sub.LsRs.multidot.scale.sub.LsRs).multidot.SL+(front.multid-
ot.b.multidot.scale.sub.C).multidot.FC
FR'=(front.multidot.a.multidot.scale.sub.LR).multidot.FR+(front.multidot.a-
.multidot.down.sub.LsRsscale.sub.LsRs).multidot.SR+(front.multidot.b.multi-
dot.scale.sub.C).multidot.FC
[0134] As previously described, although a single downmix module
can be used, a two-module implementation can increase the number of
options available, such as by including an additional downmix
opportunity, and including additional control of signal levels of
various signals. For example, as the coefficient front 804 is
increased, the overall gain of the front left (FL' 812) and front
right (FR' 814) channels can be independently controlled by
adjusting the coefficient scale.sub.LR 714 (FIG. 11). In one
embodiment, the coefficient scale.sub.LR 714 is decreased
proportionally to the increasing coefficient front 804 and the
total gain of the front left (FL' 812) and the front right (FR'
814) channels remains constant as the fader control 670 (FIG. 9) is
operated in the forward fading region 672.
[0135] The output for the surround left channel (SL' 818) according
to the signal mixer 800 can be represented as follows: 9 SL ' =
rear ( e L ' + f C ' + g Ls ' ) = ( rear e L ' ) + ( rear f C ) + (
rear g Ls ' )
[0136] Substituting L', C', and Ls' from the downmix module 700 of
FIG. 11 yields the following: 10 SL ' = rear e ( scale LR FL + down
LsRs Ls ' + down C C ' ) + rear f scale C FC + rear g scale LsRs SL
= ( rear e scale LR ) FL + ( rear e down LsRs scale LsRs + rear g
scale LsRs ) SL + ( rear e down C scale C + rear f scale C ) FC
[0137] Similarly, the output for the surround right channel (SR'
820) according to the signal mixer 800 can be represented as
follows: 11 SR ' = rear ( e R ' + f C ' + g + R s ' ) = ( rear e R
' ) + ( rear f C ' ) + ( rear g R s ' )
[0138] Substituting R', C', and Rs' from the downmix module 700 of
FIG. 11 yields the following: 12 SR ' = rear e ( scale LR FR + down
LsRs Rs ' + down C C ' ) + rear f scale C FC + rear g scale LsRs SR
= ( rear e scale LR ) FR + ( rear e down LsRs scale LsRs + rear g
scale LsRs ) SR + ( rear e down C scale C + rear f scale C ) FC
[0139] In the pure fading region 676 of FIG. 9, a pure fading
function is applied and the downmix module is effectively bypassed.
This can be achieved by setting the coefficients as follows:
scale.sub.C=scale.sub.LR=scale.sub.LsRs.noteq.0
down.sub.C=0
down.sub.LsRs=0
[0140] This yields surround left (SL' 818) and surround right
signals (SR' 820) without the downmix module deliberately
preserving center channel content as follows:
SL'=(rear.multidot.e.multidot.scale.sub.LR).multidot.FL+(rear.multidot.g.m-
ultidot.scale.sub.LsRs)
.multidot.SL+(rear.multidot.fscale.sub.C).multidot- .FC
SR'=(rear.multidot.e.multidot.scale.sub.LR).multidot.FR+(rear.multidot.g.m-
ultidot.scale.sub.LsRs).multidot.SR+(rear.multidot.fscale.sub.C).multidot.-
FC
[0141] Thus, in the pure fading region 676, center channel signal
content is not deliberately preserved when fading backward. By
design of the signal mixer 800 (FIG. 13), at least a portion of the
front left and the front right signal contents are downmixed with
the surround signal channels. However, the front left and the front
right signal contents can be dropped by setting the coefficient e
to zero. In one embodiment, center channel signal content is also
downmixed with the surround left and the surround right signals by
setting down.sub.C.noteq.0.
[0142] In the rear-fading region 674 of FIG. 9, the signals are
faded and downmixing occurs to preserve center channel signal
content. The preservation of the center channel signal content is
accomplished by setting the coefficient down.sub.C to a non-zero
value. This yields surround left and surround right signals with
preserved center channel signal content as follows:
scale.sub.LR=scale.sub.LsRs=scale.sub.LsRs.noteq.0
down.sub.C.noteq.0
down.sub.LsRs=0
SL'=(rear.multidot.e.multidot.scale.sub.LR).multidot.FL+(rear.multidot.g.m-
ultidot.scale.sub.LsRs).multidot.SL+(rear.multidot.edown.sub.C.multidot.sc-
ale.sub.C+rear.multidot.f.multidot.scale.sub.C).multidot.FC
SR'=(rear.multidot.e.multidot.scale.sub.LsRs).multidot.FR+(rear.multidot.g-
.multidot.scale.sub.LsRs).multidot.SR+(rear.multidot.e.multidot.down.sub.C-
.multidot.scale.sub.C+rear.multidot.f.multidot.scale.sub.C).multidot.FC
[0143] As previously described, although a single downmix module
can be used, a two-module implementation can increase the number of
options available, such as by including an additional downmix
opportunity, and including additional control of signal levels of
various signals. For example, as the coefficient rear 806 is
increased, the overall gain of the front left (FL') and front right
(FR') channels can be independently controlled by adjusting the
coefficient scale.sub.LR 714 (FIG. 11). In one embodiment, the
coefficient scale.sub.LR 714 is decreased proportionally to the
increasing coefficient rear 806 and the total gain of the surround
left (SL') and the surround right (SR') channels remains constant
as the fader control 670 (FIG. 8) is operated in the rear fading
region 674.
[0144] FIG. 14 is a signal processor 850 having signal coefficients
for various channels in a surround sound system that can be used
with the downmix module 700 of FIG. 11. Unlike the signal mixer 800
of FIG. 13, the signal processor 850 does not include signal
mixing. The signal processor 850 is shown in a table format to
better illustrate its operation. There are numerous analog and
digital circuit designs that can be used to implement the signal
processor 850. In one embodiment, the signal processor 850 is
positioned after the downmix module 700 of FIG. 11. However, it
should be noted that the signal processor 850 could be positioned
before the downmix module 700 or can be integrated with the downmix
module 700 in a single module implementation.
[0145] The signal processor 850 includes columns corresponding to
the output of the front left channel L' 702, the output of the
front right channel R' 704, the output of the front center channel
C' 706, the output of the left surround channel L.sub.s' 708, and
the output of the right surround channel R.sub.s' 710 of the
downmix module 700. Each of the columns includes various
coefficients that can be applied to the signals. The fade column
852 includes optional coefficients indicated as front 854 and rear
856 that can also be applied to the signals depending on the
particular fading region. The coefficients front 854 and rear 856
can vary with position of the fade control. For example, the
coefficient front 854 can increase and the coefficient rear 856 can
decrease as the fader control is faded forward.
[0146] The signal processor 850 includes rows corresponding to the
outputs of the signal processor 850. The front left output is
indicated by FL' 862, the front right output is indicated by FR'
864, the front center output is indicated by FC' 866, the surround
left output is indicated by SL' 868, and the surround right output
is indicated by SR' 870. An optional back center output is
indicated by BC' 872.
[0147] The output for the front left channel (FL' 862) according to
the signal processor 850 can be represented as follows:
FL'=front(a.multidot.L')
[0148] Substituting L' from the downmix module 700 of FIG. 11
yields the following: 13 FL ' = front a ( scale LR FL + down LsRs
Ls ' + down C C ' ) = ( front a scale LR ) FL + ( front a down LsRs
scale LsRs ) SL + ( front a down C scale C ) FC
[0149] Similarly, the output for the front right channel (FR' 864)
according to the signal processor 850 can be represented as
follows:
FR'=front(a.multidot.R')
[0150] Substituting R' and C' from the downmix module 700 of FIG.
11 yields the following: 14 FR ' = front a ( scale LR FR + down
LsRs Rs ' + down C C ' ) = ( front a scale LR ) FR + ( front a down
LsRs scale LsRs ) SR + ( front a down C scale C ) FC
[0151] In the pure fading region 676 of FIG. 9, a pure fading
function is applied and the downmix module 700 is effectively
bypassed. This can be achieved by setting the coefficients as
follows:
scale.sub.LR=scale.sub.LsRs=scale.sub.C.noteq.0
down.sub.C=0
down.sub.LsRs=0
[0152] This yields front left and front right signals without
preserving surround content as follows:
FL'=(front.multidot.a.multidot.scale.sub.LR).multidot.FL
FR'=(front.multidot.a.multidot.scale.sub.LR).multidot.FR
[0153] Thus, in the pure fading region 676, surround signal content
is not preserved when fading forward.
[0154] In the front fading region 672 of FIG. 9, the signals are
faded and downmixing occurs to preserve surround signal content.
Since front center channel content is generally present in the
forward fade position, the coefficient down.sub.c can be set to
zero. However, the coefficient down.sub.c can be set to non-zero
values if desired. The preservation of the surround signal content
is accomplished by setting the coefficient down.sub.LsRs to a
non-zero value. This yields front left (FL' 862) and front right
signals (FR' 864) with preserved surround signal content as
follows:
scale.sub.LR=scale.sub.LsRS=scale.sub.C.noteq.0
down.sub.C=0
down.sub.LsRs.noteq.0
FL'=(front.multidot.a.multidot.scale.sub.LR).multidot.FL+(front.multidot.a-
.multidot.scale.sub.LsRs).multidot.SL
FR.multidot.=(front.multidot.a.multidot.scale.sub.LR).multidot.FR+(front.m-
ultidot.a.multidot.down.sub.LsRs.multidot.scale.sub.LsRs).multidot.SR
[0155] The output for the surround left channel (SL' 868) according
to the signal processor 850 can be represented as follows:
SL'=rear(g.multidot.Ls')
[0156] Substituting Ls' 708 from the downmix module 700 of FIG. 11
yields the following:
SL'=rear .multidot.g.multidot.scale.sub.LsRs.multidot.SL
[0157] Similarly, the output for the surround right channel (SR'
870) according to the signal mixer 800 can be represented as
follows:
SR'=rear(g.multidot.Rs')
[0158] Substituting Rs' from the downmix module 700 of FIG. 11
yields the following:
SR'=rear.multidot.g.multidot.scale.sub.LsRs.multidot.SR
[0159] In this embodiment, the downmix module 700 of FIG. 11 is not
intended to preserve center channel content in the rear fading
region 674 of FIG. 9. In another embodiment (not shown), the
downmix module could be designed to preserve center channel content
in the rear fading region 674. In the embodiment shown, the fader
control 670 of FIG. 8 performs a pure fading function in the rear
fading region 674. Additionally, as previously described, a pure
fading function is applied in the pure fading region 676 of FIG.
9.
[0160] A number of embodiments of the invention have been
described. Nevertheless, it will be understood that various
modifications may be made. For example, although the systems and
techniques are described primarily in the context of automotive
listening environments, the systems and techniques are also
applicable in other listening environments. In addition, although
certain examples of control parameters are described, the systems
and techniques may be used in connection with other control
parameters that use two or more control regions to apply different
control functions for each control region.
[0161] It is evident that those skilled in the art may now make
numerous modifications and uses of the specific apparatus and
techniques herein described without departing from the inventive
concepts. Consequently, the invention is to be construed as
embracing each and every novel feature and novel combination of
features present in or possessed by the apparatus and techniques
disclosed herein and limited only by the spirit and slope of the
appended claims.
* * * * *