U.S. patent number 3,777,076 [Application Number 05/268,726] was granted by the patent office on 1973-12-04 for multi-directional sound system.
This patent grant is currently assigned to Sansui Electric Co., Ltd.. Invention is credited to Susumu Takahashi.
United States Patent |
3,777,076 |
Takahashi |
December 4, 1973 |
MULTI-DIRECTIONAL SOUND SYSTEM
Abstract
A multi-directional sound system for use in the manufacture of
matrix four channel stereophono discs comprises an encoder
including a plurality of phase shifters for shifting the phases of
a plurality of directional input signals from discrete sound
sources by angles corresponding to the directions of the sound
sources and a matrix circuit for producing two channel signals, and
a decoder for decoding the two channel signals for reproducing the
directional input signals.
Inventors: |
Takahashi; Susumu (Tokyo,
JA) |
Assignee: |
Sansui Electric Co., Ltd.
(Tokyo, JA)
|
Family
ID: |
12809857 |
Appl.
No.: |
05/268,726 |
Filed: |
July 3, 1972 |
Foreign Application Priority Data
|
|
|
|
|
Jul 2, 1971 [JA] |
|
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46/48674 |
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Current U.S.
Class: |
369/89;
G9B/20.003; 381/23 |
Current CPC
Class: |
H04S
3/02 (20130101); G11B 20/00992 (20130101) |
Current International
Class: |
G11B
20/00 (20060101); H04S 3/00 (20060101); H04S
3/02 (20060101); G11b 003/74 () |
Field of
Search: |
;179/1.4ST,1.4C,1.1TD,15BT,1GQ,1G |
Other References
scheiber, Analysing Phase-Amplitude Matrices, Audio Eng. Soc.
Preprint No. 815 (J-5), Oct. 71..
|
Primary Examiner: Cardillo, Jr.; Raymond F.
Claims
What is claimed is:
1. An encoder system for producing two channel signals suitable for
recording on a phono disc from first to fourth directional audio
input signals, said encoder system comprising:
first to fourth input terminals for receiving said first to fourth
audio input signals, respectively;
first and second output terminals from which said two channel
signals are derived, respectively;
first to fourth phase shifter means coupled to said first to fourth
input terminals, respectively, said first to fourth phase shifter
means being operative to introduce relative phase differences of
about +22.5.degree., +67.5.degree., -22.5.degree. and -67.5.degree.
between said first to fourth audio input signals;
means connected in circuit with said first phase shifter means for
coupling about 0.92 of said first audio input signal to said first
output terminal;
means connected in circuit with said first phase shifter means for
coupling about 0.38 of said first audio input signal to said second
output terminal;
means connected in circuit with said second phase shifter means for
coupling about 0.92 of said second audio input signal to said first
output terminal;
means connected in circuit with said second phase shifter means for
coupling about -0.38 of said second audio input signal to said
second output terminal;
means connected in circuit with said third phase shifter means for
coupling about 0.38 of said third audio input signal to said first
output terminal;
means connected in circuit with said third phase shifter means for
coupling about 0.92 of said third audio input signal to said second
output terminal;
means connected in circuit with said fourth phase shifter means for
coupling about -0.38 of said fourth audio input signal to said
first output terminal; and
means connected in circuit with said fourth phase shifter means for
coupling about 0.92 of said fourth audio input signal to said
second output terminal.
2. A decoder for producing first to fourth output signals from
first and second channel signals each including four audio signals
having predetermined relative amplitude ratios and relative phase
differences of about +22.5.degree., +67.5.degree. -22.5.degree. and
-67.5.degree. therebetween, said decoder comprising:
first and second input terminals for receiving said first and
second channel signals, respectively;
first to fourth output terminals from which said four output
signals are derived, respectively;
first to fourth phase shifter means coupled to said first to fourth
output terminals, respectively;
means connected to said first input terminal for coupling about
0.92 of said first channel signal to said first phase shifter
means;
means connected to said first input terminal for coupling about
0.92 of said first channel signal to said second phase shifter
means;
means connected to said first input terminal for coupling about
0.38 of said first channel signal to said third phase shifter
means;
means connected to said first input terminal for coupling about
-0.38 of said first channel signal to said fourth phase shifter
means;
means connected to said second input terminal for coupling about
0.38 of said second channel signal to said first phase shifter
means;
means connected to said second input terminal for coupling about
-0.38 of said second channel signal to said second phase shifter
means;
means connected to said second input terminal for coupling about
0.92 of said second channel signal to said third phase shifter
means; and
means connected to said second input terminal for coupling about
0.92 of said second channel signal to said fourth phase shifter
means.
3. A decoder according to claim 2 wherein said first to fourth
phase shifter means are operative to introduce between input
signals thereto relative phase differences of about -22.5.degree.,
-67.5.degree., +22.5.degree. and +67.5.degree..
4. A decoder according to claim 2 wherein said first to fourth
phase shifter means are operative to introduce between input
signals thereto relative phase differences of about 0.degree.,
-90.degree., 0.degree. and 90.degree..
Description
This invention relates to a multi-directional sound system for
encoding multi-channel sound signals into two channel signals and
then decoding the two channel signals back into the multi-channel
sound signals.
Matrix four channel stereo record systems have been developed which
use a two-channel transmission system for the purpose of
reproducing sounds from a two-channel stereo-phono disc with an
enhanced sensation of presence. In each prior system, however, it
is not possible to perfectly decode two channel signals into four
channel signals.
In preparation of a matrix 4-channel stereo disc, the front-left
and front-right sounds in a sound field are recorded on the disc by
the horizontal movement of a sound groove cutter receiving two
channel left signals L and right signals R, and the rear-right and
rear-left sounds by the vertical movement of the cutter. Since a
two-channel transmission system or disc is used, cross talks
inevitably occur between the channels. However, the reproduced
sounds are separated into respective channels and are heard as if
they come from four discrete directions by the sense of
listeners.
It is an object of this invention to provide an improved encoding
system capable of converting directional multi-channel signals into
two channel signals without an appreciable cross-talk.
Another object of this invention is to provide an improved decoding
system for use in combination with the encoding system.
According to one aspect of this invention there is provided an
encoding system for forming two channel signals in accordance with
input signals from a plurality of directive sound sources, which
comprises a plurality of input terminals connected to receive the
input signals respectively; two output terminals; a plurality of
phase shifters connected to the input terminals, each phase shifter
acting to shift the electrical phase of the input signal from each
sound source by an angle corresponding to an angle equal to one
half of the positional angle of the sound source; means connected
between the output sides of respective phase shifters and a first
output terminal for multiplying the output of each phase shifter
with a sine of an angle equal to one half of the positional angle
of a corresponding sound source; and means connected between the
output sides of respective phase shifters and a second output
terminal for multiplying the output of each phase shifter with a
cosine of an angle equal to one half of the positional angle of a
corresponding sound source.
According to another aspect of the invention there is provided a
decoder system for producing reproduced outputs corresponding to
the input signals from the sound sources from the two channel
signals formed by the encoding system described above, said decoder
system comprising a pair of input terminals connected to receive
the two channel signals; output terminals of the same number as the
sound sources; first means connected between the first input
terminal and respective output terminals for multiplying the first
input signal applied to the first input terminal with a sine of an
angle equal to one half of the positional angle of a corresponding
sound source; second means connected between the second input
terminal and respective output terminals for multiplying the second
input signal applied to the second input terminal with a cosine of
an angle equal to one half of the positional angle of a
corresponding sound source; and phase shifters connected between
the first and second means and the output terminals for
compensating for the phase shift provided by said encoder.
In accordance with further aspect of this invention there is
provided a multi-directional sound system comprising a combination
of the encoder and decoder described above.
The present invention can be more fully understood from the
following detailed description when taken in connection with
reference to the accompanying drawings, in which:
FIG. 1 is a graph showing a vector diagram for cutting a matrix
four channel stereo record;
FIG. 2 is a diagram showing a square sound field;
FIG. 3 is a graph showing another example of a vector diagram for
cutting a matrix four channel stereo record;
FIG. 4 is a cutting vector diagram useful to explain the cross-talk
which occurs when manufacturing a conventional matrix four channel
record;
FIG. 5 shows a cutting vector diagram useful to explain the
cross-talk which occurs when manufacturing a matrix four channel
stereo record in accordance with this invention;
FIG. 6 is a diagram showing multi-directional sound fields;
FIG. 7 shows a connection diagram of one example of the encoder
embodying the invention;
FIG. 8 shows a connection diagram of a decoder constructed in
accordance with the invention; and
FIG. 9 shows a connection diagram of a modified decoder.
To aid better understanding of the invention, one example of a four
channel recording system will first be described.
FIG. 1 shows cutting vectors which are utilized for cutting four
channel signals FR (front right), FL (front left), RL (rear left)
and RR (rear right) obtained from a square sound field shown in
FIG. 2 on a two channel stereo disc. Cutting vectors L and R of the
conventional stereo signals intersect at right angles and these
vectors are on the opposite sides of the horizontal or front axis.
Signals RL and FL on the left hand side of the sound field and
signals FR and RR on the right hand side of the sound field are
recorded with a cutting angle of 22.5.degree. with respect to
signals L and R respectively. Each signal vector has an angle of
directivity equal to an integer multiple of a cutting angle or
matrix angle of 22.5.degree. measured from the front axis. Since
vectors of signals FL and RR and vectors of signals RL and FR
intersect with each other at right angles respectively, there is no
appreciable cross-talk between channels which are on diagonals of
the reproduced sound field. The expression "cutting angle" as used
herein refers to the direction of motion of the cutter stylus, and
not to the angle of the tip of the cutter.
However, as can be clearly noted from these cutting vectors, when
the sound source is positioned at the rear center of the sound
field, or where signals RR and RL have equal magnitude and
frequency the resultant vector of these signals will be in the
direction of the horizontal axis so that the sound in the rearward
direction of the sound field will be recorded as the sound in the
forward direction.
To obviate this defect, a cutting method as shown in FIG. 3 has
been proposed. According to this method the resultant vector of
signals RL and RR is directed in the direction of the vertical or
rear axis so that above described defect can be eliminated. This
method, however, is not advantageous in that when four channel
signals have the same magnitude and frequency, the resultant vector
will always be in the single direction, that is the direction of
vector L.
In order to obviate this difficulty, a third method has been
proposed according to which the phase of the signal RL utilized in
the first method is shifted by 90.degree. to produce a signal jRL
and the phase of signal RR is shifted by -90.degree. to form a
signal -jRR. According to this third method the composite vector of
signals RL and RR cuts the disc in the vertical direction, whereas
the composite vector of signals FL and FR, cuts in the horizontal
direction. For this reason, even when four channel signals have the
same magnitude and frequency the resultant vector depicts a circle
so that these signals are not recorded as a sound in a single
direction as in the second method. According to the third method,
however, the sounds in the direction of L in the sound field, that
is the sounds producing the signals FL and RL produce a cross-talk
component in the direction R. When signals FL and RL are identical
with each other and signals FR and RR are zero the resultant vector
of signals RL and FL will depict an ellipse as shown in FIG. 4
since the signals FL and RL are different in phase by 90.degree..
This means that the sound groove cutter is moved along an ellipse
even though there is no signal of the right component. As a result,
the elliptical movement of the sound groove cutter produces a
cross-talk in the direction R.
Let us now consider the degree of separation between signals L and
R at the time of cutting.
The resultant signals L and R are expressed by the following
equations:
L = cos22.5.degree..sup.. FL + jcos22.5.degree..sup.. RL +
sin22.5.degree..sup.. FR -(-j)sin22.5.degree..sup.. RR
R = sin22.5.degree..sup.. FL - jsin22.5.degree..sup.. RL +
cos22.5.degree..sup.. FR + (-j)cos22.5.degree..sup.. RR
Assuming now that signals FR and RR equal zero and signals FL and
RL are expressed by sin pt, the resultant signals L and R are given
by the following equation:
L = 0.92(sin pt + cos pt)
= 0.92 .sqroot.2 sin (pt + 45.degree.)
= 1.3sin(pt + 45.degree.)
R = 0.38(sin pt - cos pt)
= 0.38 .sqroot.2 sin(pt - 45.degree.)
= 0.535sin(pt - 45.degree.)
Accordingly, the degree of separation is given by
r = L/R = 2.42 = 7.7 db.
When a cutting is made with two channel signals produced by the
encoding system it is possible to improve the degree of separation
between signals L and R.
According to this invention, four channel signals FL, RL, FR and RR
obtained from the square sound field are utilized to produce two
channel signals L and R expressed by the following equations:
L = cos.theta..sup.. FL.angle..theta. + cos.theta..sup..
RL.angle.3.theta. + sin.theta..sup.. FR.angle.-.theta. -
sin.theta..sup.. RR.angle.-3.theta. (1)
r = sin.theta..sup.. FL.angle..theta. - sin.theta..sup..
RL.angle.3.theta. + cos.theta..sup.. FR.angle.-.theta. +
cos.theta..sup.. RR.angle. -3.theta. (2)
where .theta. represents the cutting angle of 22.5.degree. shown in
FIG. 1 and FL.angle..theta. means that the phase angle of signals
FL is shifted by .theta. electrical degrees. The angle .theta. is
positive when it is measured in the counterclockwise direction from
the front axis shown in FIG. 1. Resultant signals L and R are
applied to a conventional stereo sound groove cutter to cut the
walls of the sound groove of a disc which intersect with each other
at right angle.
As clearly shown in the equations (1) and (2), the four channel
signals FL, RL, FR and RR are phase shifted by electrical angles
which are equal to respective cutting angles. Accordingly, in this
case, if signals FL and RL are the same (sin pt) and signals FR and
RR are equal to zero, above described equations for L and R are
rewritten as follows:
L = 0.92sin(pt+.theta.) + 0.92sin(pt+3.theta.)
= 0.92[sin(pt+2.theta.)cos.theta. - cos(pt+2.theta.)sin.theta.
+ sin(pt+2.theta.)cos.theta. + cos(pt+2.theta.)sin.theta.]
= 0.92 .times. 2 cos.theta..sup.. sin(pt+2.theta.)
= 1.7sin(pt+2.theta.)
R = 0.38sin(pt+.theta.) - 0.38sin(pt+3.theta.)
= 0.38[sin(pt+.theta.).sup.. cos.theta. - cos(pt+2.theta.).sup..
sin.theta.
- sin(pt+2.theta.)cos.theta. - cos(pt+2.theta.).sup..
sin.theta.]
=-0.38 .times. 2 sin.theta..sup.. cos(pt+2.theta.)
= -0.29cos(pt+2.theta.)
= 0.29cos(pt-2.theta.)
Thus, L/R - 5.9 = 15.4 db and the cross-talk characteristic is
greatly improved. In this case, the resultant vector of signals FL
and RL depicts an ellipse as shown in FIG. 5.
Above described equations (1) and (2) are obtained from the square
sound field shown in FIG. 2. The equation for encoding a plurality
of directional input signals from a multi-directional sound field
shown in FIG. 6 is as follows: ##SPC1##
where .phi..sub.1 represents the angle indicating the position of a
sound source M.sub.1, that is the positional angle of a microphone
or sound source M.sub.1 shown in FIG. 6 as measured from the
abscissa in the counterclockwise direction and E.sub.1 the
magnitude of the voltage produced by this microphone. The term e
shows the angle of phase shift of signal E.
Equations (1) and (2) are obtained by putting
.phi./2=.pi./4+.theta. in equation (3). Although equations (1) and
(2) are expressed in terms of the cutting angle they can be
expressed in terms of the positional angle of the sound source. As
evident from the equation (3), the signal L is obtained by
multiplying the magnitudes of respective signals with a sine of an
angle equal to one half of the positional angle of the signal
source, shifting the electrical angles of the resulting signals by
an angle corresponding to one half of the positional angle and
adding the phase shifted signals whereas the signal R is obtained
by multiplying the magnitudes of respective signals with a cosine
of an angle equal to one half of the positional angle of the signal
source, shifting the electrical angles of the resulting signals by
an angle corresponding to one half of the positional angle and
adding the phase shifted signals.
Four channel signals FL', FR', RL' and RR' from a disc on which the
two channel signals L and R shown by equations (1) and (2) have
been recorded are decoded in the following manner by means of a
decoder.
FL' = (cos.theta..sup.. L + sin.theta..sup.. R).angle.-.theta.
= 0.85.sup.. FL + 0.85.sup.. RL.angle.2.theta. + 0.35.sup..
FR.angle.-2.theta.
- 0.35.sup.. RR.angle.-4.theta. + 0.15.sup.. FL - 0.15.sup..
RL.angle.2.theta.
+ 0.35.sup.. FR.angle.-2.theta. + 0.35.sup.. RR.angle.-4.theta.
= FL + 0.7.sup.. RL.angle.2.theta. + 0.7.sup..
FR.angle.-2.theta.
FR' = (sin.theta..sup.. L + cos.theta..sup.. R).angle..theta.
= 0.7.sup.. FL.angle.2.theta. + FR + 0.7 RR.angle.-2.theta.
RL' = (cos.theta..sup.. L - sin.theta..sup.. R).angle.-3.theta.
= 0.7.sup.. FL.angle.-2.theta. + RL + 0.7.sup..
RR.angle.2.theta.
RR' = (-sin.theta..sup.. L + cos.theta..sup.. R).angle.3.theta.
= 0.7.sup.. RL.angle.-2.theta. + 0.7.sup.. FR.angle.2.theta. +
RR
The signals decoded in this manner are respectively applied to
loudspeakers on the left hand side in the forward direction, on the
left hand side in the rearward direction, on the right hand side in
the forward direction and on the right hand side in the rearward
direction in the reproducing field thereby producing four channel
stereo sounds.
FIG. 7 shows one example of the encoder constructed in accordance
with this invention. In this figure, reference numerals 1, 2, 3 and
4 show input terminals of the encoder which are connected to
receive four channel signals FL, RL, FR and RR, and reference
numerals 7, 8, 9 and 10 show phase shifters connected to
corresponding input terminals, the phase shifter 7 shifts the phase
of signal FL by the cutting angle .theta.(22.5.degree.), or an
angle obtained by subtracting 45.degree. from one half of the
positional angle of the sound source (135.degree., in this case),
that is 22.5.degree.. A symbol .phi. depicted in the blocks
represents a reference angular quantity which is introduced for
providing easy phase shift operation of the audio signals and may
be considered to be equal to zero degree in operation. The output
from the phase shifter 7 is multiplied with a cosine of the cutting
angle .theta. by means of a resistor means or potentiometer R.sub.1
and thence supplied to an output terminal 5 adapted for the signal
L. Cos.theta. is equal to the sine of the angle of one half of the
positional angle of the FL sound source (135.degree.), that is
sin67.5.degree.. In other words, the resistor means R.sub.1
multiplies the output from phase shifter 7 with a sine of the angle
equal to one half of the positional angle of the FL sound source.
Further, the output from phase shifter 7 is multiplied with the
sine of the cutting angle .theta. by means of a resistor means
R.sub.5 and is then applied to an output terminal 6 adapted for the
signal R. The resistor means R.sub.5 may be considered to multiply
the output from phase shifter 7 by a cosine of an angle equal to
one half of the positional angle of the FL sound source.
The phase shifter 8 functions to shift the phase of signal RL by
3.theta. degrees (67.5.degree.) which is equal to the difference
between one half of the positional angle 22.5.degree. of the sound
source RL and 45.degree.. The output from phase shifter 8 is
multiplied with cos.theta. (cos22.5.degree.=0.92) by means of a
resistor means R.sub.2 and is then applied to the output terminal
5, where cos.theta. is equal to the sine of one half of the
positional angle 22.5.degree. of the sound source RL
(sin112.5.degree.=0.92). The output from phase shifter 8 is
multiplied with sin.theta. by means of a resistor means R.sub.6 and
is then applied to the output terminal 6 through a phase inverter
11. The function of resistor means R.sub.6 and inverter 11 is
equivalent to multiply the output from phase shifter 8 with the
cosine of an angle equal one half of the positional angle
225.degree. of the RL sound source (cos112.5.degree.= -0.38).
In this manner, the output terminal 5 is supplied with a sum of
signals obtained by multiplying signals which are phase shifted by
an electrical angle equal to the difference between an angle equal
to one half of the positional angles of the sound source and
45.degree., with the sine of an angle equal to one half of the
positional angles of the sound sources, whereas the output terminal
6 is supplied with a sum of the signals obtained by multiplying
signals which are shifted by an electrical angle equal to the
difference between an angle equal to one half of the positional
angles of the sound sources and 45.degree., with the cosine of an
angle equal to one half of the positional angles of the sound
sources.
The decoder will now be described with reference to FIG. 8. The
signal L supplied to an input terminal 15 of the decoder is
multiplied with cos.theta. by means of a resistor means R.sub.16.
The signal R applied to input terminal 16 is multiplied with
sin.theta. by means of a resistor means R.sub.19 and the outputs
from the resistor means R.sub.16 and R.sub.19 are mixed with each
other. The phase of the mixed signals is shifted by -.theta. by the
action of phase shifter 21 thus supplying to output terminal 17 a
reproduced signal FL' corresponding to signal FL. The resistor
means R.sub.16 operates to multiply the signal L with the sine of
an angle equal to one half of the positional angle 135.degree. of
FL signal source for the purpose of producing reproduced signal
FL', whereas the resistor means R.sub.19 multiplies the signal R
with the cosine of an angle equal to one half of the positional
angle of FL signal source. Accordingly, another reproduced output
can be obtained by forming a mixed signal consisting of a signal
which is produced by multiplying the signal L with the sine of an
angle equal to one half of the positional angle of the
corresponding sound source and a signal which is produced by
multiplying the signal R with the cosine of an angle equal to one
half of the positional angle of the corresponding sound signal, and
shifting the phase of the mixed signal in the opposite direction by
an angle equal to the angle of phase shift provided on the encoder
side.
Phase shifters 21, 22, 23 and 24 on the decoder side are provided
for the purpose of cancelling the phase shift provided by the phase
shifters on the encoder side. Although it is ideal to shift back
the phase by the same electrical degrees the angles of phase shifts
.theta. and 3.theta. on the decoder side may be 0.degree. and
90.degree., respectively.
In a modified decoder shown in FIG. 9, there are provided phase
splitters 26 and 27 and a resistance network including resistors
R.sub.9 and R.sub.15 inclusive.
Although the invention has been shown and described in terms of
some preferred embodiments thereof, it will be clear that many
changes and modifications will be obvious to one skilled in the art
without departing from the true spirit and scope of the invention
as defined in the appended claims. Thus, for example, although the
invention is particularly suitable as an encoding system of two
channel systems used for manufacturing matrix four channel
stereophono disc, this system can also be used in a two channel
transmission system for applications other than two channel
stereophono discs, such as an FM stereo broadcasting system, a
wired broadcasting system or two track stereo tape recorder
system.
* * * * *