U.S. patent number 3,646,574 [Application Number 05/040,335] was granted by the patent office on 1972-02-29 for compatible stereo generator.
Invention is credited to Howard S. Holzer.
United States Patent |
3,646,574 |
Holzer |
February 29, 1972 |
**Please see images for:
( Certificate of Correction ) ** |
COMPATIBLE STEREO GENERATOR
Abstract
This invention relates to an instrument incorporating an
otherwise independent pair of wide band unity gain amplifier chains
of novel configuration providing in the several stages of each
chain the capability of and means for shifting the phase of signals
from stereophonic signal sources applied to each chain. The phase
shift capability of one channel is over the range of zero phase
shift related to the phase of the input signal through + 90.degree.
and in the other channel over a range of from zero phase shift
related to the phase of the input signal through - 90.degree.. The
wide band phase shift networks are an element in the implementation
of a means to apply the discovery disclosed in this invention that
if the signal output of each respectively, of a pair of related
stereophonic signal channels is applied to one, respectively, of
said amplifier chains, one of the channels containing signals
identified as A+ C, and the other containing signals identified as
B+ C (the C-components of the signals being common to both
channels) and the signal of the first channel shifted in phase +
60.degree. while that in the second channel is shifted in phase -
60.degree. (the difference between the two being a total of
120.degree. centered about a zero input reference phase) then the
summation of the phase shifted signals from the two channels will
result in an output (summed) signal of A+ B+ C, whereas by prior
art techniques the summation or mixing of two stereophonic channels
produces a resultant A+ B+ 2C.
Inventors: |
Holzer; Howard S. (Canoga Park,
CA) |
Family
ID: |
21910441 |
Appl.
No.: |
05/040,335 |
Filed: |
May 25, 1970 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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696249 |
Jan 8, 1968 |
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Current U.S.
Class: |
381/27 |
Current CPC
Class: |
H04S
3/00 (20130101) |
Current International
Class: |
H04S
3/00 (20060101); H04r 005/00 () |
Field of
Search: |
;330/307
;179/1G,1GP |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Claffy; Kathleen H.
Assistant Examiner: Olms; Douglas W.
Parent Case Text
This application is a continuation in part of application Ser. No.
696,249 filed Jan. 8, 1968 by this applicant under the same title
and now abandoned.
Claims
What is claimed as new is:
1. A compatible stereophonic signal generator operable from a pair
of stereophonically related signal sources wherein each of said
pair of sources provides a common signal component, said generator
comprising:
a first cascade of phase-shift audio amplifiers for wide band phase
shifting the common signal component from one of said signal
sources, said first cascade having connected therein adjustable
resistor capacitor networks adapted to vary the phase of signals
applied thereto over a predetermined range of frequencies;
a second cascade of phase shift amplifiers for wide band phase
shifting the common signal component from the other of said signal
sources, said second cascade having connected therein adjustable
resistor capacitor networks adapted to vary the phase of signals
applied thereto over said predetermined range of frequencies;
said first and second cascades of phase shift amplifiers
maintaining a substantially constant phase difference between the
phase shifted common signal components, whereby upon being combined
for monophonic reproduction, said phase shifted common signal
components exhibit a combined signal magnitude less than the sum of
the individual common signal component magnitudes.
2. The signal generator of claim 1 wherein said phase difference is
90.degree..
3. The signal generator of claim 1 wherein said phase difference is
120.degree..
4. The signal generator of claim 1 wherein each cascade of phase
shift amplifiers comprises three phase shift amplifiers.
5. The signal generator of claim 1 wherein the frequency ranges for
the respective cascade phase shift amplifiers are set for
approximately 30 to 300 Hz., 300 to 3,000 Hz. and 3,000 to 30,000
Hz., respectively.
6. The signal generator of claim 1 wherein for each cascade all the
resistors of said adjustable, resistor capacitor, phase shift
networks include variable portions, said generator further
including a common shaft with the variable portions being connected
to said shaft so as to be commonly adjustable with a single manual
operation.
7. A compatible stereophonic signal generator operable from a pair
of stereophonically related audio signal sources, each of the pair
having at least a signal component common to both said sources,
said generator comprising:
a first wide band phase shift generator having an input circuit, a
first cascade of phase shift amplifiers connected to said input
circuit, each of said amplifiers in said first cascade having
connected therein adjustable resistor capacitor, phase shift
networks adapted to vary the phase of signals applied thereto over
a predetermined range of frequencies;
a second wide band phase shift generator having an input circuit, a
second cascade of phase shift amplifiers connected to said input
circuit, each of said amplifiers in said second cascade having
connected therein adjustable resistor capacitor, phase shift
networks adapted to vary the phase of signals applied thereto over
the same predetermined range of frequencies as defined for said
first phase shift generator;
said first and second wide band phase shift generators producing
respective phase shifted signals which differ in relative phase by
a substantially constant phase difference;
said input circuit of said first wide band phase shift generator
being connected to one of said pair of signal sources;
said input circuit of said second wide band phase shift generator
being connected to the other of the pair of signal sources.
8. The signal generator of claim 7 wherein said first and second
wide band phase shift generators shift the phase of said common
signal components by equal and opposite amounts respectively
independently of frequency.
9. The signal generator of claim 7 wherein said amounts are
+45.degree. and -45.degree., respectively.
10. The signal generator of claim 7 wherein said amounts are
+60.degree. and -60.degree., respectively.
11. The method of producing compatible two-channel stereophonic
signals from first and second stereophonically related signals each
containing at least a common signal component, said method
comprising the steps of:
phase shifting the common signal component of said first signal to
provide a first phase shifted common signal component;
phase shifting the common signal component of said second signal to
provide a second phase shifted common signal component differing in
phase from said first phase shifted common signal component by a
substantially constant phase angle; and combining said phase
shifted common signal components, for monophonic reproduction, to
result in a combined component having an amplitude less than the
sum of the amplitudes of the individual common signal
components.
12. In the method defined in claim 11, the additional step of
applying said first and second phase shifted components to
respective impedance-matching networks.
13. In the method defined in claim 11, the additional step of
combining said first and second phase shifted common signal
components in a mixing arrangement, whereby a resultant summed
common signal is produced which retains substantially the original
composition obtained in the initial performance from which said
stereophonic related signals were derived.
14. The method of producing compatible two-channel stereophonic
signals from first and second stereophonically related signals,
said first and second related signals containing, respectively,
components A+ B and B+ C wherein the C signal components are
common, said method comprising the steps of:
applying the A+ C component to a first phase-shifting network;
applying the B+ C component to a second phase-shifting network;
phase shifting the A+ C component applied to the first phase shift
network over a predetermined phase angle to provide a phase shifted
A+ C component;
phase shifting the B+ C component applied to the second phase-shift
network to provide a phase shifted B+ C component, the phase of the
C component in the B+ C phase shifted component differing from the
phase of the C component in the A+ C phase shifted component by a
substantially constant phase angle; and
so combining said A+ C and said B+ C components as to provide a
compatible stereophonic signal wherein said C component in the
combined signal is less than the algebraic sum of the C components
in said A+ C and said B+ C components.
Description
BACKGROUND OF THE INVENTION
In stereophonic recording and audio amplifying systems generally,
the ultimate output signals which the listener consumer of
stereophonic records utilizes are divided into left and right
channels. From the standpoint of the manufacturers of such records
two markets must be served by the records he produces. One record
must be provided for the two-channel stereophonic record playing
listener consumer and another record for the monophonic equipment
owner providing only a single output channel. This process
necessarily doubles his manufacturing costs since in prior art
systems the stereophonic recording is not compatible with the
monophonic system. Therefore the need for separate stereophonic and
monophonic records, at present, for any performance.
By the prior art techniques in order to be able to make monophonic
as well as stereophonic forms of the same program material the
initial live recording is made in three channels which can be
designated as channels A, B, and C respectively. The A-channel is
the "left channel" or that which receives the signals from a
microphone to the listeners' left during a performance and the
B-channel is the "right channel" or that which receives the signals
from a microphone at the listeners' right during a performance.
From either a third microphone, centrally placed, or, by virtue of
a matrixing network electrically incorporated in the recording
system, a C-channel is produced which contains signal components of
the same performance which are common to both the left (A) channel
and the right (B) channel.
Thus, when a two-channel stereophonic record is produced from the
master three-channel performance record, the respective channels
may be said to include in the one A+ C components, and in the other
B+C signal components.
When the monophonic record version of this performance is made by
the prior art technique the channels are mixed so that the two
channels add up as follows: A+ C (left channel)+B+ C (right
channel). The summation resultant is A+ C+ B+ C which equals A+ B+
2 C.
To the listener this is appreciated as a rather prominent center
presence which is unnatural because the C-component of the signal
is stronger than either the A- or B-components thereof. The
monophonic recording, therefore, so made, has a character unlike
the original performance in that the C-components of the signal
information differ from their natural relationship in the original
performance.
It is therefore desirable to find means for producing a
stereophonic recording that will permit the resulting recorded
two-channel signal when mixed together for monophonic records or
when a stereophonic recording is played on monophonic playback
equipment the resultant output will have equal A-, B- and
C-components as in the original recording session. The present
invention provides a means usable in the recording process or in
other related stereophonic systems by which the two-channel
stereophonic phonograph record resulting therefrom can be played
back on monophonic equipment without the above-mentioned unnatural
presence.
DESCRIPTION OF THE INVENTION
This inventor has discovered a property of phase shifting networks
applied in stereophonic audio apparatus whereby the previously
described signal components A+ C and B+ C can be summed and will
only add up to A+ B+ C. A means has also been devised whereby the
discovery can be implemented and applied easily and economically to
two-channel systems which include the aforementioned A+ C and B+ C
components where the C-component is common to both channels.
The implementation provides circuit means for phase shifting the A+
C signal in one direction while the B+ C signal is phase shifted in
the opposite direction.
The newly discovered property is the fact that when the A+ C signal
channel shifts the phase of the applied signal by +60.degree. and
the B+ C channel shifts the phase of the applied signal by
-60.degree. when these two channels are mixed, either electrically
to produce a single channel output for a monophonic recording, or
mechanically by playing back the stereophonic two-channel recording
produced with phase shifted signals as above-mentioned recorded
thereon, the resultant monophonic output signal adds to A+ B+
C.
The phase shifting above referred to will affect only the common
C-components of the signal since the A- and B-signals have no
counterpart in the respective opposite channels. The effective
phase shift of the A- and B-signals in their respective channels is
of no consequence and therefore produce absolutely no degradation
of the stereophonic signals in the use of the invention.
The particular novelty achieved in the invention is the fact that
the phase shifting is accomplished without distortion. It has been
found that the respective equal positive and negative phase shift
of the signals in the respective channels from a zero input
reference phase is responsible for this. A 120.degree. or for that
matter, any total phase shift of the signals in one channel without
change in the other will produce a distorted signal in the
resultant when they are combined. Only the equal and opposite phase
shifts from the zero reference to a maximum of +90.degree. for one
channel and -90.degree. for the other channel produces the desired
result. The system operates without adding distortion or degrading
the stereophonic character of the signals.
It has been found also that when the common information signals are
different in amplitude and shifted in phase over equal and opposite
angles in each channel the resultant summed amplitude is never
greater than the larger of the two and its apparent phase angle is
shifted in proportion to the ratio between the amplitudes.
Accordingly it is an object of the invention to provide a pair of
phase-shifting amplifiers each capable of shifting the phase of
signals applied thereto in opposite directions equally about a zero
phase reference related to the input signal to each channel.
It is another object of the invention to provide means for
producing a two-channel stereophonic signal capable of being
combined for monophonic reproduction without distortion and without
degradation of the stereophonic character thereof, and which when
combined will encompass all of the components of the original
performance without amplitude change.
It is a further object of the invention to provide means by which
the common component C of respective stereophonic audio channels A+
C and B+ C will, when the two channels are combined not be
augmented due to summation effects.
It is still another object of the invention to implement the
discovery that when stereophonic signals A+ C and B+ C are
respectively shifted in phase in opposite directions by 60.degree.
in their respective channels, in the subsequent summation of the
channels in the resultant will be A+ B+ C.
It is an even further object of the invention to provide a
phase-shifting network of two independent channels which produce in
respective stages thereof phase shifts for decades of frequencies
in a predetermined spectrum, and the phase shifts are equal and
opposite in polarity with respect to a zero reference input phase
in each respective channel, the phase adjustment of all of the
stages in both channels being accomplished with a single control
mechanically operative for all of the stages and arranged for
precise tracking in all channels. By governing the phase shift in
equal angles and opposite directions for the respective channels,
the common information C therein for selected angles between
0.degree. and 90.degree. can be controlled from the value of 2 C to
zero when the channels are added together by mixing.
These and other objects of the invention will become more clear
from the specification which follows when taken together with the
appended claims. The specification describes a preferred embodiment
of the implementation of the invention shown in the drawings but
should not be construed as limiting the invention to the embodiment
shown since those skilled in the arts appertaining thereto will be
able to devise other ways of implementing the invention in the
light of the teachings herein within the ambit of the claims.
IN THE FIGURES
FIG. 1 is a basic block diagram of a system according to this
invention;
FIG. 2 is a block diagram showing the mixing and amplification of
signals in accordance with the invention;
FIG. 3 is a circuit schematic diagram of the opposite polarity
phase shift networks devised for implementing the invention;
FIG. 4 is a waveform diagram illustrative of the discovery involved
in the invention;
FIG. 5 is a vector diagram illustrative of the operation of the
invention;
FIG. 6 is a vector diagram of other relationships involved in the
implementation of the invention; and
FIG. 7 is a schematic circuit diagram showing details of one
section of the phase shift networks of the implementation of the
invention to illustrate an alternative mode of phase
adjustment.
The basic principle of the invention implementation is illustrated
in the block diagram of FIG. 1. In the Figure a Source A is
indicated in block 10 and a source B in block 11. These sources may
be the left channel and right channel signal sources of a common
stereophonic program. The program may be the result of a tape
recording, a live performance, a disc recording or any other
stereophonic signal source, such as an AM or FM stereophonic
broadcast signalling system. In any event the source consists of a
pair of channels each carrying its respective signal information
related to the stereophonic program material. These source signals
are applied on signal lines 13, 14 to separate inputs 15, 16 on the
compatible stereophonic generator of this invention indicated by
block 17. From the output of the generator 17 there may be derived
the A-output signal on line 18, the B-output signal on line 20. By
adding the signals on lines 18 and 20 by any known means such as a
pair of resistances 21, 26 a monophonic compatible output may be
derived on line 19.
As is indicated in blocks 10, 11 the signal sources A and B each
include a common component C so that channel A as indicated in FIG.
2 has signal components A+ C and channel B has signal components B+
C. The A-channel "A" components are not found in channel B nor are
the "B" components found in channel A.
In the compatible stereo generator block 17 are included phase
shift networks to shift the phase of the respective channel signals
in opposite polarity with an adjustment capability through
+90.degree. in the A-channel and through -90.degree. in the
B-channel simultaneously.
As may be seen in FIG. 2 amplifier devices 93, 94 may be added to
the outputs of channels A and B on lines 18, 20 for any purpose
such as impedance matching, power or voltage amplification or
simply for isolation. The devices which perform such functions are
well known in the art and can be selected from a wide variety of
commercial sources of such equipment. They must each, however, be
identical in circuit and performance with the other.
The outputs of amplifier or other devices 93, 94 may be connected
to a mixing network of conventional design 25 to produce the
compatible signal output on line 29 identified as (A+ B+ C).
The compatible stereophonic generator 17 according to this
invention and shown in a schematic circuit diagram in FIG. 3
consists of two-phase shift networks 91, 92. Each network includes
three cascaded phase shift stages, transistors 33, 39, 46 in 91 and
transistors 63, 69, 76 in 92. Each stage produces up to a + or -
90.degree. shift in phase for a selected decade of frequencies, by
setting the controls 37, 44, 52 in 91 and 67, 74, 82 in 92 all six
on a common shaft 90. For example, the first stage of the positive
going phase shift network operates to shift the phase over the
frequencies from 30,000 to 3,000 Hz. The second stage produces the
phase shift for frequencies from 3,000 to 300 Hz. The third stage
covers the frequencies from 300 to 30 Hz. Similarly the negative
going phase shift network produces a phase shift in the first stage
over 30,000 to 3,000 Hz. The second stage produces a phase shift
over the range 3,000 to 300 Hz. The third stage produces the
negative phase shift over the frequency range 300 to 30 Hz. The
phase shift in each stage is identical in each network. The
resistances and capacitances such as at 36 37, 38 which form the
feedback paths between collector and emitter of the respective
transistor stage such as 33 in which they are connected, are
selected in combination with the transistor impedance parameters to
produce the desired phase shift range where adjustable components
are used. If as may be desirable in some cases fixed value
resistors as shown in FIG. 7 are to be employed the choice will be
predicated upon the X.sub.c value of the capacitor such as 36 or 66
over the frequency range of interest and the transistor amplifier
parameters. While the range above-mentioned covering 30-30,000 Hz.
will clearly be adequate for audio frequency stereophonic sound or
broadcasting systems a unit has been produced in the process of
proving the operation of the system of the invention. A four stage
device was constructed in which the frequency decade separation
started at 10 Hz. and continued through 100 kHz. as follows:
1st stage 100 kHz. to 10,000 Hz.
2nd stage 10,000 Hz. to 1,000 Hz.
3rd stage 1,000 Hz. to 100 Hz.
4th stage 100 Hz. to 10 Hz.
The principle enunciated above is followed in the same way in
selecting the resistance and capacitance values so that the phase
shift operation of the amplifier is accomplished.
It is certainly clear from the above that a wide band phase shift
network similar to those shown in dashed blocks 91, 92 is possible
using the designs and principles hereinabove set forth and
employing the circuit configurations shown in FIG. 3. Such wide
band networks according to the invention can be employed in video
systems as in other systems where such wide range positive and
negative phase shift capabilities are called for.
Each of the frequency decade amplifier phase shift units has unity
gain so that the overall gain of each network chain such as 91, 92
is unity. Stated another way, there is no insertion loss to speak
of in the use of the network chain. The variable resistor such as
37, 44, 52 and 67, 74 82 in the feedback loop is chosen so that it
will vary in relation to the X.sub.c of the capacitor such as 36,
42, 50 or 66, 72, 80 for that particular loop from the lowest
frequency of the decade to the highest frequency of the decade so
that the X.sub.c from the top of the decade to the bottom of the
decade can either go from zero phase shift to +90.degree. phase
shift in one unit (say channel A) and from zero phase shift to
-90.degree. phase shift in the other (channel B) unit. It should be
noted that the resistance units used in the adjustment of phase
shift, however the network is used, that is, in fixed values, as in
FIG. 7 (37a, 44a) or as adjustable potentiometer units, as in FIG.
3 their values must be precise and the tracking of the six
potentiometers, tied to a common shaft 90, must be exact with
respect to one another to accomplish the sought for + and -
90.degree. phase shift variation capability. On the input of each
of the phase shift networks an amplitude control 30, 31 or 60, 61
is provided so that adjustment of the amplitude of the signals
applied to each channel can be made in the event that the signal
levels from the respective right and left channels of the source of
the stereophonic signals should fail to be balanced, that is should
not be of equal amplitude. An emitter follower amplifier at 54, 84
provides a low-output impedance.
While in the exemplary unit an impedance of 5,000 ohms (Resistor
86) at the output of each channel is provided other means may be
employed to either step-up or stepdown the impedances to desired
levels as suits the channel combining or mixing networks such as 25
or other systems to which this equipment is to be connected.
Additionally integrated circuit amplifier units or other amplifiers
can be added at the output of each channel before mixing to provide
either power output or driver output for power stages or to produce
unity gain power output conditions as desired.
The waveform diagram in FIG. 4 is illustrative of an important
factor in the operation of the system of this invention, that is,
that the resulting A+ B+ C is obtained upon mixing after the
settings of the phase-shifting networks 91, 92 are so adjusted that
a phase separation of 120.degree. is maintained between the signals
of the two channels with respect to their initial input phase, that
is the right channel signal is shifted -60.degree. in phase with
respect to its input phase by the network 17 and the left channel
signal is shifted -60.degree. with respect to its input phase. Thus
the 120.degree. phase difference is created. The signals are
maintained 120.degree. apart at all times irrespective of anything
else that may be taking part elsewhere in the stereophonic system.
This phase difference between the two channels, once set, is
invariant with respect to one another.
It should be further further noted that the advance of phase in one
channel has a corresponding retardation in phase in the other
channel starting from an identical zero reference phase in each
channel. The system does not operate simply on the basis of a
difference in phase between the two channels amounting to
120.degree. or any other phase difference. The difference must be
arranged to depart equally in a negative and positive direction
from either the identical zero phase or 360.degree. starting phase
points at the input 15, 16 to the phase shift networks. For example
a 120.degree. difference all on the positive side or all on the
negative side of the initial starting (zero or 360.degree.) phase
does not produce the result disclosed in this invention. Hence it
is the belief of this inventor that he has discovered a phenomenon
not heretofore known in this art, namely that where in a first
signal channel (A) containing signal components A and C and a
second signal channel (B) containing signal components B and C, the
signal components C being common to both channels, (though the
channels are otherwise independent and separate) are each
respectively shifted in phase in opposite directions by 60.degree.
(the total phase difference being 120.degree. centered over the
zero phase point) and the channels thereafter added, the resultant
of this summation is A+ B+ C with the C-component returning to zero
phase.
Had the addition of the two channels been done by any of the known
prior art techniques the resultant would have been A+ B+ 2 C which
is the expected algebraic result.
Mathematically the new result can be explained as follows:
Given the common signal C appearing in both channels. For the
purposes of the ensuing discussion the A-signal and the B-signal
can be ignored because each passes on through its respective
channel without interaction with the other, albeit each goes
through the same phase-shifting operation respectively applied to
the cochannel C-signals in the channel with it.
The C-signal in channel A is phase shifted +60.degree. which may be
described as a shift of .pi./3 radians.
The C-signal in channel B is phase shifted -60.degree. which may be
described as a shift of -.pi./3 radians.
Upon mixing of the two signals they are summed:
sin (C- .pi./3)+sin (C+ .pi./3)
=(sin C.sup.. cos .pi./3+cos C.sup.. sin .pi./3)+(sin C.sup.. cos
.pi./3-cos C.sup.. sin .pi./3)
=2 (sin C.sup.. cos .pi./3)
=2.sup. . 1/2 sin C=sin C
The C-signal component has therefore a value of unity rather than 2
C which is obtained by an algebraic addition without phase
shift.
In FIG. 5 there is shown a vector diagrammatic representation of
the effect discovered and hereinabove disclosed. In the figure
there is presented the vector or radius line 100 to represent the
amplitude (value of 1 unit) of the C-component in the A+ C channel
rotated in phase counterclockwise 60.degree. from the 360.degree.
or 0.degree. reference line 101 to the 300.degree. point 102 on an
arbitrary reference circle. The radius line 103 represents the
amplitude (value of 1) of the C-component in the B+ C channel
rotated in phase clockwise from the 360.degree./0.degree. reference
60.degree. to 60.degree. point on the arbitrary reference circle.
Forming the vector parallelogram as indicated by dashed lines 105,
106, shows that the radius line 107 on the 0.degree. or 360.degree.
axis is 1 unit long falling as it does on the reference circle.
Radius line 107 represents the vector sum of the two vectors 100
and 103 and is equal in length to each of lines 100 and 103.
It has been noted in the introductory remarks that when the
amplitudes of the C-components in the respective left and right
channels differ from one another, the phase-shifting operation
produces, upon summation a resultant not greater than the largest
amplitude and the reference phase shifts towards the side with the
larger of the two C-component values. This is illustrated in FIG. 6
where line 110 is shown similar to line 100 of FIGS. 5 but where
the amplitude of the line 110 is but 0.5 in value. The line 111 in
FIG. 6 is the same as line 103 in FIG. 5. By the parallelogram
technique it can be shown that the resultant vector sum (line 112)
has a value of 0.86603 which can be computed from trigonometric
tables since the angle of the line 112 is now at +30.degree..
From the above it can be seen that by selecting a particular phase
shift angle in the negative direction for one of the channels and
another angle in the positive direction for the other channel or
alternatively using equal phase shifts in opposite polarities for
the two channels the amplitude of the C-component is represented by
the lines 107 in FIG. 5 and 112 in FIG. 6 may be controlled when
the channels are combined. This C-component amplitude in the
combined signal can be as little as zero where the shifts are equal
and opposite at 90.degree. giving a difference of 180.degree.
between the components. Where there is no shift and the two
channels containing C-components are combined the C-components add
to the sum of their values in each channel. Thus, if C-component
has a value of 1 in each channel the summation value will be 2 C.
If the value of the nonphase shifted C-components are respectively
1 and 0.5 the resultant combined value will be 1.5.
The chart below indicates the combined summation values of
C-components of equal amplitudes therein for equal and oppositely
phase shifted channels according to this invention containing A+ C
and B+ C respectively:
Equal phase shift Summed value of angles C components
__________________________________________________________________________
.+-.0.degree. 2.000 .+-.15.degree. 1.932 .+-.30.degree. 1.732
.+-.45.degree. 1.414 .+-.60.degree. 1.0 .+-.75.degree. 0.517
.+-.90.degree. 0.
__________________________________________________________________________
It can be seen therefore that using the phase-shifting device 17 of
this invention for any angle between 0.degree. and .+-.90.degree.
for the respective channels A+ C and B+ C, the equal amplitude
component C can be controlled in combined A+ B+ NC resultant where
N is twice the cosine of the equal and opposite angles through
which the phase is rotated. In mathematical terms N in this case
can be described as
N = 2 cos .+-. .theta.
where .theta. is the angle equal and opposite of phase shift for
each channel.
The practical implication of this result is that by the use of the
invention herein disclosed any desired proportionate relationship
between zero and 2.0 can be imparted to the C-component when the
two stereo channels containing the C-component in each are combined
to produce a monophonic resultant.
One example might be given of a shift in phase of one channel
counterclockwise to 270.degree. with the other channel at
360.degree., the phase difference between the two phase shifted
signals being a total of 90.degree.. The amplitude of the C-signal
component on the 270.degree. line is 1.7. The amplitude of the
C-component signal on the 360.degree. line is 1.0. The diagonal,
similar to that of line 112 in the arbitrary circle of FIG. 6, for
the resulting rectangular parallelogram in the above example will
equal 2.0 indicating that upon mixing the two channels after the
phase difference settings, the C-component as combined will have an
amplitude value of 2.0. The angle of the above-mentioned diagonal
will be at 300.degree.. The diagonal is the vector summation
line.
The principles of the invention can be expressed also in such terms
that one can compute both the shift in angle of reference and the
resultant amplitude or either of them for any conditions other than
equal and opposite phase shift in the two channels or differences
in amplitudes of the C-component of the two channels.
If one sets .PHI. to represent the lagging angle and .theta., the
leading angle of the shifted signals and A as the amplitude of the
signal shifted by angle .PHI. and B the amplitude of the signal
shifted by angle .theta., then one can compute the new vector angle
of the combined signal and the new amplitude A.sub.x of the
C-components in the combined signal as follows:
Tan X (the new vector angle) = (A cos .PHI. + B cos .theta.)/(B sin
.theta. - A sin .PHI.)
A.sub.x (the new amplitude) = sin X (A cos .PHI. + B cos .theta.) +
(cos X B sin .theta. -A sin .PHI. )
With the above formulas one can compute the vector summation lines
such as 107 of FIG. 5 or 112 in FIG. 6. The length of lines 107 or
112 then represent A.sub.x in the above formulas.
The system described hereinabove might be called a stereophonic
signal logic device which recognizes the common signal components
in the channels of a stereophonic system and permits combining the
channels externally in such fashion that the amplitude of the
common signal component never exceeds its original occurrence in
the live program from which the stereophonic material was
derived.
The significance of the invention to the recording and broadcast
industries is that stereophonic program material can be broadcast,
recorded or played back in such a manner that the program, as heard
monophonically, from a monophonic receiver or monophonic record
playback system will still have the same balance and quality as in
the original live performance sans only the directional
character.
This means that the identical recording can be played back with
either stereophonic or monophonic equipment without compromise of
the stereophonic quality or monophonic quality as related to the
live performance.
The new device may be used during the original recording or in the
preparation of masters for phonograph discs to produce a compatible
record or tape which can be played or broadcast either
stereophonically or monophonically, or if broadcast
stereophonically can be received on monophonic equipment with no
depreciation in quality.
It may also be used by recording studios or broadcasters to play
existing stereophonic recordings to produce a compatible
stereophonic signal which can be received or played back on
monophonic equipment without degradation.
The device makes no change in stereophonic quality, adds no
distortion nor loss in signal-to-noise ratio.
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