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Claims  |
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What is claimed is:
1. A sound reproduction system for converting encoded stereo signals on
input channels A and B into signals on left, supplemental left, center,
right, supplemental right, and surround output channels, respectively,
comprising:
a left output channel for producing output signals from said stereo signals
on said input channels A and B with enhanced level of steered signal
intended to come from the left direction and reduced level of steered
signals intended to come from other directions;
a supplemental left output channel for producing output signals similar in
level (intensity) to output signals of said left output channel and with
reduced steered signal level for left direction signals;
a center output channel for producing signals with enhanced level of
steered signal components in said stereo signals on said input channels A
and B that are intended to come from the center direction and reduced
level of steered signals intended to come from other directions;
a right output channel for producing output signals from said stereo
signals on said input channels A and B with enhanced levels of steered
signals intended to come from the right direction and reduced level of
steered signals intended to come from other directions;
a supplemental right output channel for producing output signal similar in
level (intensity) to output signal on said right output channel and with
reduced steered signal level for right direction signals; and
a surround output channel for producing output signals with enhanced levels
of steered signal components intended to come from the surround direction
and reduced level of steered signals intended to come from other
directions.
2. The system of claim 1 wherein each of said left, right, center and
surround channels includes means for detecting the intended signal
direction and enhancing the level of the steered signals in that
direction.
3. The system of claim 1 wherein said encoded stereo signals on said input
channels A and B include directional (steered) components and
non-directional (unsteered) components.
4. The system of claim 1 wherein said left output channel includes first
combining means for combining said input signal on said A channel with a
modified first attenuated signal, a modified third attenuated signal and a
modified fourth attenuated signal to produce said left output;
said right output channel includes second combining means for combining
said input signal on said B channel with a modified second attenuated
signal, a modified third attenuated signal, and a modified fourth
attenuated signal to produce said right output;
said center output channel includes third combining means for combining
said input signals on said A and B channels with a modified third
attenuated signal, said first attenuated signal and said second attenuated
signal to produce said center output;
said surround output channel includes fourth combining means for combining
said input signals on said A and B channels with a modified fourth
attenuated signal, said first attenuated signal and said second attenuated
signal to produce said surround output;
said supplemental left output channel includes fifth combining means for
combining said input signal on said A channel with a modified first
attenuated signal, a modified third attenuated signal, a modified fifth
attenuated signal and a modified sixth attenuated signal to produce said
supplemental left output; and
said supplemental right output channel includes sixth combining means for
combining said input signal on said B channel with a modified second
attenuated signal, and modified fourth, fifth and sixth attenuated signals
to produce said supplemental right output.
5. The system of claim 1 wherein each of said supplemental left and right
output channels includes a delay for delaying signals on said supplemental
channels relative to signals on said left, center, right and surround
output channels.
6. A sound reproduction system for converting encoded stereo signals on
input channels A and B into signals on left, supplemental left, right, and
supplemental right output channels, respectively, comprising:
a left output channel for producing output signals intended to come from
the left direction;
a supplemental left output channel for producing output signals similar in
level (intensity) to output signals of said left output channel and with
reduced steered signal level for left direction signals;
a right output channel for producing output signals intended to come from
the right direction; and
a supplemental right output channel for producing output signals similar in
level (intensity) to output signals on said left output channel and with
reduced steered signal level from right direction signals.
7. The system of claim 6 wherein
said supplemental left output channel includes first combining means for
combining said input signal on said A channel with a plurality of modified
attenuated signals to produce said supplemental left output; and
said supplemental right output channel includes second combining means for
combining said input signal on said B channel with a plurality of modified
attenuated signals to produce said supplemental right output.
8. The system of claim 6 wherein each of said supplemental left and right
output channels includes a delay for delaying signals on said supplemental
channels relative to signals on said left and right output channels.
9. The system of claim 8 wherein said encoded stereo signals on said input
channels A and B include directional (steered) components and
non-directional (unsteered) components.
10. The system of claim 8 and further including
a center output channel for producing signals with enhanced level of
steered signal components signals with signal on said input channels A and
B that are intended to come from the center direction and reduced level of
steered signals intended to come from other directions; and
a surround output channel for producing output signals with enhanced levels
of steered signal components intended to come from the surround direction
and reduced level of steered signal intended to come from other
directions.
11. The system of claim 10 wherein each of said supplemental left and right
output channels includes a delay for delaying signals on said supplemental
channels relative to signals on said left and right output channels.
12. A sound reproduction system for converting encoded stereo signals on
input channels A and B into signals on left, supplemental left, center,
right, supplemental right, and surround output channels, respectively,
comprising:
means for attenuating the input signal on the A input channel as a function
of the difference of the logs of the signals on the A and B input channels
to produce first and second attenuated signals,
means for attenuated the input signal on the B input channel as a function
of the difference of the logs of the signals on the A and B input channels
to produce third and fourth attenuated signals,
means for attenuating the sum of the input signals on the A and B input
channels as a function of the difference of the logs of the sum and
difference of the signals on the A and B input channels to produce a fifth
attenuated signal,
means for attenuating the difference of the signals on the A and B input
channels as a function of the difference of the logs of the sum and
difference of the signals on the A and B input channels to produce a sixth
attenuated signal, means for attenuating the input signal on the A input
channel for actively reducing all steered signals, while preserving levels
of unsteered signals to produce a seventh attenuated signal,
means for attenuating the input signal on the B input channel for actively
reducing all steered signals, while preserving levels of unsteered signals
to produce an eighth attenuated signal,
and means for combining the signal on the A input channel, the signal on
the B input channel, the sum of the signals on the A and B input channels,
the difference of the signals on the A and B input channels, and said
first, second, third, fourth, fifth, sixth, seventh and eight attenuated
signals to produce left, supplemental left, center, right, supplemental
right and surround outputs.
13. The system of claim 12 wherein said combining means includes first
combining means for combining said input signal on said A channel with
modified first, third and fourth attenuated signals to produce said left
output;
second combining means for combining said input signal on said B channel
with modified second, third and fourth attenuated signal to produce said
right output;
third combining means for combining said input signals on said A and B
channels with modified first, second and third attenuated signals to
produce said center output;
fourth combining means for combining said input signals on said A and B
channels with modified first, second and fourth attenuated signals to
produce said surround output;
fifth combining means for combining said input signal on said A channel
with modified first, third, fifth and sixth attenuated signal to produce
said supplemental left output; and
sixth combining means for combining said input signal on said B channel
with modified second, fourth, fifth and sixth attenuated signals to
produce said supplemental right output.
14. The system of claim 13 wherein each of said supplemental left and right
output channels includes a delay for delaying signals on said supplemental
channels relative to signals on said left, center, right and surround
output channels.
15. The system of claim 14 wherein said encoded stereo signals on said
input channels A and B include directional (steered) components and
non-directional (unsteered) components. |
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Claims |
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Description |
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SOUND REPRODUCTION
This invention relates to sound reproduction systems, and more particularly
to systems for converting two channel input signals to multiple channel
output signals.
Most films made at present utilize a two channel distribution system for
sound. This system consists of an encoder used when the film is mixed,
which takes four inputs, Left, Center, Right and Surround (or rear), and
with a passive matrix mixes these four inputs into two output channels.
The two channel mix thus derived is played back through a decoder which
attempts to recreate the original four channels from the incoming two.
Both during the mixing, and later when the film is screened, the speaker
arrangement is carefully standardized. The center channel loudspeaker is
always located behind the center of the screen, so the majority of dialog
will appear to come from the center of the screen regardless of where a
listener is located in the theater. The left and right main speakers are
also located behind the screen, but at the left and right edges. The
apparent location of sound effects, and sometimes dialog, is panned
between the left, center and right of the screen by controlling the
relative level of sound in those three speakers. For any particular
direction only one or at most two speakers are used. One of the main jobs
of a decoder used with this system is to prevent leakage of sound which
should only come from one or two of these loudspeakers into the others.
Such leakage destroys the directional illusion for listeners who are not
in the center of the theater.
The fourth, or Surround, channel is fed in parallel to an array of
loudspeakers which surrounds the whole audience, both at the rear and the
sides of the theater. Since these speakers are all wired together it is
not possible to make a sound effect which comes from a particular side or
rear direction with this system and the surround channel is only used for
sound effects when a overall sound is wanted such as an ambience effect,
for example the sound of the ocean during a beach or marine scene, or
motor noise in a vehicle. Such sounds are usually mixed so they come from
all the loudspeakers, including the ones behind the screen. Specific
effects which are intended to come from the surround channel only are
rare. In current films the major signal in the surround channel is music,
which is usually mixed so at least some of the sound comes from around the
listener. Depending on the taste of a particular director or sound mixer,
music may be relatively equally loud in all loudspeakers, or may have a
bias toward the front--i.e., it is mixed so the surround speakers are at a
somewhat lower level than the front loudspeakers.
This surround system has a number of disadvantages, especially when such a
system is adapted to use in the home. One of the major disadvantages is
that the main left and right loudspeakers are confined to the width of the
screen. There has been considerable research into listener preference for
music signals, which has shown that the optimal angle between the listener
and the two main speakers should be plus and minus thirty degrees or more.
Research into concert hall acoustics has also shown that it is desirable
to have as much sound as possible travelling laterally--from left to right
or right to left across the listener's head. Such lateral sound is
provided in a general way by the standard surround array which extends to
the sides of the listener, but due to the fact that both the left and
right sides of the surround system are being driven by the same signal,
and the usual rather low level of signals in the surround channel, this
array does not produce adequate lateral energy from film music. The left
and right main speakers, which carry the bulk of the music energy, subtend
a narrow angle to the front of the typical listener. In the home, if the
left and right speakers are placed close to the edges of a typical video
screen, they are even closer together, and produce a very cramped musical
image with little lateral sound energy. The most direct way of increasing
the lateral sound energy during film or music playback is to spread the
left and right speakers wider outside the screen. This works well for
music, but sound effects and occasional panned dialog will then appear to
come from a much wider area that the area occupied by the screen. Such
differences between the width of the visual and audio fields is bothersome
to some people.
In accordance with one aspect of the invention, there is provided a system
for converting encoded stereo signals, on input channels A and B into six
output signals, consisting of the normal left, center, right and surround
signals and at least two supplemental output channels. These supplemental
channels produce outputs nearly identical to the main left and right front
channels when music is being played with the addition of a small time
delay, but reject sound effects and panned dialog. The supplemental
channels are used to drive speakers placed in the forward part of the side
walls of a theater, or to the sides of a listener in the home. Even when
music is mixed to be predominantly in the front, the supplemental channels
have adequate level to make music sound wider and more spacious, while
effects and dialog panned anywhere inside the screen stay where they
belong.
Previous decoders, for example of the type disclosed in U.S. Pat. No.
4,862,502 (hereinafter the '502 patent), the disclosure of which is
expressly incorporated herein by reference, detect the intended direction
of a signal and then enhance the level of the signal in that direction.
The supplemental channels of a system in accordance with the current
invention tend to eliminate signals for which an intended direction can be
established. If there is only one signal coming into the signal converting
system for example a monaural sound effect in the absence of music, the
outputs of the supplemental channels are zero regardless of where the
sound mixer directs the signal. The supplemental channels are fully active
whenever signals such as music are present which are intended to come from
many directions. When both a directional signal and non directional music
are present at the same time, the supplemental channels smoothly reduce
the level of the directional signal without changing the apparent level of
the music.
Tests of decoders built in accordance with this invention have shown that
these new supplemental channels when played through loudspeakers located
on the sides of a listener are useful not only for surround encoded films,
but for normal stereo music.
This advantage appears to remain even if the front left and right signals
are not decoded (equal to the A+B inputs) and the center and surround
channels are eliminated.
In accordance with another aspect of the invention, there is provided a
sound reproduction system for converting encoded stereo signals on input
channels A and B into signals on left, supplemental left, right, and
supplemental right output channels, respectively, that includes a left
output channel for producing output signals intended to come from the left
direction; a supplemental left output channel for producing output signals
similar in level (intensity) to output signals of the left output channel
and with reduced steered signal level for left direction signals; a right
output channel for producing output signals intended to come from the
right direction; and a supplemental right output channel for producing
output signals similar in level (intensity) to output signals on the left
output channel and with reduced steered signal level for right direction
signals.
Preferably, the supplemental left output channel includes first combining
means for combining said input signal on said A channel with a plurality
of modified attenuated signals to produce said supplemental left output;
and the supplemental right output channel includes second combining means
for combining said input signal on said B channel with a plurality of
modified attenuated signals to produce said supplemental right output; and
each of the supplemental left and right output channels includes a delay
for delaying signals on the supplemental channels relative to signals on
the left and right output channels. The encoded stereo signals on the
input channels A and B include directional (steered) components and
non-directional (unsteered) components.
In particular embodiments, decoder logic detects the intended direction of
a sound from information encoded in the two input channels, enhances the
level of that sound in the output channels which are closest to the
intended direction, and attenuates that sound in the other output
channels. For example, if a sound is to appear to be half way between the
center and the left loudspeakers in a standard four channel film decoder,
the two channel input for such a signal would consist of the same signal
in both channels, but with the left channel somewhat louder than the
right. With a passive decoder, where the center channel is simply the left
plus the right channel, and the surround channel is the left minus the
right, this sound would come from all four loudspeakers, and would be only
vaguely located. An active decoder would enhance the signal in the left
and the center loudspeakers, while eliminating it from the right and the
surround loudspeakers. There are several ways to do active decoding in
common practice. Certain of these methods, and the one in the '502 patent,
have an additional desirable property in that the level of music or
unsteered material is preserved in all speakers, at the same time as
signals which are intended by the film producer to be steered to a
particular direction are reduced or removed.
It is useful to think of the two inputs to the decoder as consisting of the
sum of two types of signals. One, typically dialog or effects, is at least
6 to 10 dB louder than the other type of signal, and is intended to come
from only one particular direction. This signal is relatively easy to
detect by finding the ratio of the left input level to the right input
level, as well as the level ratio of the center to the surround channels
(left plus right to left minus right). Signals where one or both of these
ratios is significantly different from unity may be termed STEERED.
The second type of signal is intended to come approximately equally from
all channels, and is characterized by having little or no correlation
between the two input channels. That is, the ratio of the left level to
the right level, as well as the ratio of the left plus right to the left
minus right are both about unity. This second type of signal is typically
music or an over-all environmental sound effect, and may be termed
UNSTEERED.
A signal converting system in accordance with this invention includes an
output which actively reduces all steered signals, while preserving the
level of unsteered signals. For example, when a loud sound effect is mixed
directly into the left input channel, along with uncorrelated music in
both input channels, the sound effect will appear enhanced in the regular
left output channel, but will be actively removed from the supplemental
left output channel. In the supplemental output channel, music energy from
the left input which is lost when the sound effect is attenuated is
replaced with music energy from the right channel, thus preserving the
apparent loudness of the music in the supplemental output.
This reduction of steered signals from the supplemental channels while
preserving the apparent loudness of unsteered signals preferably occurs
regardless of the encoded direction of the steered signal, so no steered
signal will appear at the supplemental outputs. In a particular
embodiment, this technique is used to derive two new (supplemental)
channels, one which is equivalent to the delayed left input for unsteered
signals, and one which is equivalent to the delayed right input. These
channels are connected to loudspeakers located at the sides of the
listeners, with the normal surround speakers mostly behind the listener.
The regular left, center and right speakers are located in their standard
positions near the screen. (In a particular embodiment, the surround
channel is also divided inside the decoder into two decorrelated outputs,
so that there are seven channels available from the decoder.) Music and
environment effects appear wide and rich, surrounding the listener
dramatically, while sound effects stay localized to the screen. The
results are similar to the sound from a six or seven channel film system
such as Imax or Todd AO, but can be used in the home with the great number
of films available in two channel surround format. The decoder can also
easily be installed in a theater.
In a preferred embodiment, the system includes a left output channel for
producing output signals from the stereo signals on the input channels A
and B with enhanced level of steered signals intended to come from the
left direction and reduced level of steered signals intended to me from
other directions; a supplemental left output channel for producing output
signals similar in level (intensity) to output signals of the left output
channel and with reduced steered signal level for left direction signals;
a center output channel for producing signals with enhanced level of
steered signal components in the stereo signals on the input channels A
and B that are intended to come from the center direction and reduced
level of steered signals intended to come from other directions; a right
output channel for producing output signals from the stereo signals on the
input channels A and B with enhanced levels of steered signals intended to
come from the right direction and reduced level of steered signals
intended to come from other directions; a supplemental right output
channel for producing output signals similar in level (intensity) to
output signals on the right output channel and with reduced steered signal
level for right direction signals; and a surround output channel for
producing output signals with enhanced levels of steered signal components
intended to come from the surround direction and reduced level of steered
signals intended to come from other directions.
In a particular embodiment, the input signals are fed into four logarithmic
level detectors, one each for the left input level A, the right input
level B, the left plus right input level, and the left minus right input
level. From the output of these detectors, four control signals are
derived. Each of these control signals has a value which varied smoothly
from zero to one as the ratio of the input levels varies. As an example,
the left control signal is zero unless the ratio of the left input level
to the right input level is greater than one, and varies smoothly from
zero to one as this ratio increases above one. The other signals are
similar--each is zero unless the input signal associated with the control
signal is larger than its opposite signal, and it rises smoothly to one as
its input signal ratio rises.
In the embodiment described in the '502 patent, the control signals all
have the same mathematical shape, and as can be seen from the above
description, only two of the four signals are non-zero at any one time. To
derive or understand their mathematical shape we need to consider only one
set of directions, such as all directions between the left main
loudspeaker and the center speaker. As the direction of a signal varies
from left to center the left control signal varies from one to zero, and
the center control signal varies from zero to one. As a convenience for
mathematical description a direction pointer t can be derived which is an
angle between left and center, where t=.phi. is equivalent to full left,
and t=45.degree. is equivalent to full right. The input signals to the
decoder can be the encoded such that:
left input A=cos(t)*sig
right input B=sin(t)*sig
where t is a direction pointer which varies from 0 degrees to 45 degrees
(t=0 is equivalent to full left, t=45 is equivalent to center), and "sig"
is the audio signal. For the purposes of analysis, the signal "sig" can be
assumed to be a sine wave of constant unity amplitude. Since this
sinusoidal signal will be common to all inputs and outputs only the
direction determining elements cos(t) and sin(t) are retained in the
following discussion.
The input signal has the property that the total energy in both channels is
constant as the direction pointer t changes: A.sup.2 +B.sup.2 =1 and that
when t=45 degrees sin(t)=cos(t)=1/.sqroot.2. This is the standard film
encoding.
The decoder detects the encoded direction t by finding the ratio of the
input levels, such that:
t=arctan (level A/level B)
t is defined for directions between left and center Both the decoder
described in the '502 patent and this patent are symmetric in their
design--and it is sufficient to consider their behavior in only one
quadrant to derive the shape of the control signals in the other
quadrants. In each quadrant the angle t will have a different but related
meaning. As a pan from left to center is performed, the left control
signal will start at one (full left) and decay to zero; the right control
signal will always be zero, since the ratio of the right input to the left
input is always less than one; the surround or left minus right control
signal is also always zero; and the center or left plus right control
signal will vary from zero to one. The left output of the decoder should
vary from a maximum at t=0 to zero at t=45, while the center output varies
from zero at t=0 to a maximum at t=45, and the right output and the
surround output are zero. If A=cos(t) and B=sin(t) in the equations given
below for the right output and the rear output of the decoder, and these
two outputs are set to zero, the functional form for the left control
signal and the center control signals can be derived. The left control
signal is given by:
left control signal=((cos(t)-sin(t))/cos(t))=GL
for 45 degrees>t >0 ONLY
Similarly, the functional form of the center control signal is:
center control signal=(sin(t)/(cos(t)+sin(t))=GC
as t varies from 45 to 0
By symmetry these two shapes must be the same, but one is increasing while
the other is decreasing.
The right (GR), center (GC), and rear (GS) control signals all have the
same functional shape, and can be determined simply by knowing the ratio
of the various input levels. For any input signal at least two of the
control signals are always zero. In working with these formulas
mathematically the results as a signal varies from quadrant to quadrant
should be considered separately.
The four control signals derived in this way are used to control variable
gain amplifiers, and the outputs of these amplifiers are combined to get
the four outputs of the decoder. The outputs can be written as follows:
If the left input is given by A
the right input by B
the left control signal is GL
the right control signal is GR
the center control signal is GC
the rear control signal is GS
the various outputs are given by:
left output=A+0.41*A*GL-0.5*(A+B)*GC-0.5*(A-B)*GS
right output =A+0.41*B*GR-0.5*(A+B)*GC+0.5*(A-B)*GS
center output=A+B+0.41*(A+B)*GC-A*GL-B*GR
rear output=A-B+0.41*(A-B)*GS-A*GL+B*GR
If A=cos(t) and B=sin(t) are substituted into these formulae, the outputs
have the desired properties. For example, if a signal varies from left to
center (t varies from 45 degrees to 0) the right output and the rear
outputs are always zero, and the left and center outputs are enhanced by 3
dB (1.41) as desired.
In accordance with the invention, two supplemental outputs are added--left
supplemental and right supplemental. While there are a number of ways of
constructing outputs with the desired properties, a simple and useful one
is the following:
left supplemental=A-A*GSL-0.5*(A+B)*GC-0.5*(A-B)*GS-B*GL
right supplemental=B-B*GSR-0.5*(A+B)*GC+0.5*(A-B)*GS-A*GR
These outputs have some similar elements to the standard left and right
outputs, but two supplemental terms are introduced in each output and
there are two new control signals, GSL and GSR.
GSL=GL*((1-sin(t))/cos(t))
GSR is similarly related to GR, but with t defined to match the ratio of
right level to left level.
If we assume as before:
A=cos(t)*sig
B=sin (t)*sig
we see that the new outputs have the desired properties--that is:
left supplemental=right supplemental=.phi. for all values of t from .phi.
to 45.degree.. Thus these new outputs reject signals steered between left,
center, and right.
For unsteered signals, where
GSL=GL=FR=GL=GS=GSR=.phi.
the supplemental outputs are simply equal to the A and B inputs
respectively.
In addition, if we assume:
A=cos(t)*sig+delta1
B=sin(t)*sig+delta2
where delta1 and delta2 are assumed to be not correlated with each other,
at least 10 dB lower in level than sig, and approximately equal in level,
it can be shown that the sum of delta1 squared and delta2 squared in the
left side and right side outputs is approximately constant as t varies.
This shows that music signals will be relatively little affected as
steered signals are removed from these two outputs.
Although the two side outputs are zero for signals panned from left to
center and from center to right, this is not true of signals panned from
left to rear, or from right to rear. The decoder has been tested and the
only discerned effect is to cause some leakage between the side outputs
and the rear output.
The new decoder adds some complexity to the four channel decoder of the
'502 patent as it involves four additional gain multiplies, and two new
control signals. Only two of these four multiplies are active at a time,
so the total number of active gain control devices at any time in the
decoder is four, instead of two as in the '502 decoder. In a digital
implementation the computational burden of the additional multiplies or
the additional control signals is not large, since they can be easily
derived from the signals already present through a suitable look-up table.
Additional hardware is required for the additional output sums and the two
new outputs.
Other features and advantages of the invention will be seen as the
following description of a particular embodiment progresses, in
conjunction with the drawings, in which:
FIG. 1 is a simplified block diagram of an encoder of the Dolby type;
FIG. 2 is a simplified block diagram of a stereo decoder in accordance with
the invention; and
FIG. 3 is a block diagram of decoder logic employed in the decoder system
of FIG. 2.
Description of Particular Embodiment
With reference to FIG. 1, a Dolby surround encoder includes L (left) input
on line 10, R (right) input on line 12, C (center) inputs on lines 14, 16,
and S (surround) input on line 18. The L input and a 0.707 C input are
applied to summing circuit 20 and its output is applied on line 22 to
phase compensation circuit 24 whose output is applied on line 26 to
summing circuit 28 that produces A output on line 30. The R input on line
12 is similarly applied to summing circuit 32 and combined with a 0.707 C
input for application on line 34 to phase compensation circuit 36 whose
output on line 38 is applied to subtractor circuit 40 which has an output
on line 42 as the B signal. The surround signal S on line 18 is applied to
phase shift circuit 44 whose output on line 46 is supplied (.times.0.707)
to summing circuit 28 and subtractor circuit 40 to provide output signals
A and B on lines 30, 42, respectively.
Ignoring the phase shift common to all inputs, the encoder shown in FIG. 1
is characterized by the encoding equations:
A=L+0.707C-j0.707S; and
B=R+0.707C+j0.707S,
where the j coefficient denotes an idealized frequency-independent
90.degree. phase shift.
The A and B signals are applied to the decoder system shown in FIG. 2 on
lines 50, 52, respectively. The A signal on line 50 is passed through
variable delay circuit 54 and gain circuit 56 for application to input 58
of decoder 60. The B signal on line 52 is passed through variable delay
circuit 62 and gain circuit 64 for application to input 66 of decoder 60.
Decoder 60 has an A output on line 70, an attenuated A.sub.a output on line
72, a B output on line 76, an attenuated B.sub.a output on line 78, an
attenuated C.sub.a output on line 74, an attenuated S.sub.a output on line
80, an attenuated A.sub.c output on line 82, an attenuated B.sub.y output
on line 84, an attenuated A.sub.x output on line 86, and an attenuated
B.sub.d output on line 88. Those output signals are applied to a combining
matrix that includes combining units 92, 94, 96, 98, 100 and 1 | | |
