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JPH05191886

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DESCRIPTION JPH05191886
[0001]
[Industrial application field]
[0002]
The present invention relates to a surround microphone system for defining a sound source to be
recorded and recording a surround signal when recording is performed using a microphone on a
recording medium of an audio-visual apparatus.
[0003]
2. Description of the Related Art A conventional stereo microphone system will be described with
reference to FIG.
Sound waves W1 and W2 emitted from the sound source 1 to be recorded in this figure are
picked up by the first and second microphone units 2 and 3 separated by a distance D to become
electric signals S1 and S2. It is recorded. FIG. 11 shows an example of the directivity
characteristics of the microphone units 2 and 3. Curves shown by a solid line and a broken line
are the characteristics of the stereo microphone unit when the directional sensitivity
characteristic is a curve of cardioid. In addition, the microphone unit said here is comprised using
single or multiple microphones which convert the sound wave radiated | emitted by space into an
electric signal.
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[0004]
Assuming that the angle to the central axis of directivity is θ, the cardioid is a circle whose
center is at a point whose center is ± 1/2 apart from the center in the direction of the central
axis in a circle of radius 1 centered on the origin. The two circles of the above are added, and in
the equation using polar coordinates, it is expressed as (1 + cos .theta.) / 2. In order to perform
stereo recording using two sets of microphone units having cardioid directional characteristics,
as shown in FIG. 11, the opening angle of the two microphone units is preferably 131 degrees
according to the following document It is said. STANLEY P. LIPSHITZ "STEREO MICROHONE
TECHNIQUES" J.A.E.S. Vol. 30, No. 10, 1982 Oct 707-718
[0005]
However, in the microphone unit of such a configuration, there is a disadvantage that the
direction range of the sound source to be recorded is limited only to the front. In addition, when
the direction range of the sound source to be recorded is 360 degrees including the front and
back, the method of setting the opening angle is clarified when the number of such microphone
units is temporarily used four. It was not.
[0006]
The present invention has been made in view of such conventional problems, and it is an object
of the present invention to provide a surround microphone system capable of faithfully collecting
a sound radiated in space while maintaining a sense of localization and sound. Do.
[0007]
According to the invention of claim 1 of the present application, the first microphone unit having
nondirectional directivity characteristics is disposed with its central axis shifted substantially by
90 degrees, and the directional characteristics are the same. A surround microphone unit
including the second, third, fourth and fifth microphone units that draw a curve of cardioid, an
attenuation circuit that attenuates the output of the first microphone unit, and a second that
inverts the output of the second microphone unit The first inversion circuit, the second inversion
circuit which inverts the output of the third microphone unit, the third inversion circuit which
inverts the output of the fourth microphone unit, and the output of the fifth microphone unit A
fourth inverting circuit, a first adding circuit for adding the output of the attenuation circuit, the
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output of the second microphone unit, and the output of the third inverting circuit, and an
attenuation circuit The second addition circuit that adds the output of the third microphone unit
and the output of the fourth inversion circuit, the output of the attenuation circuit, the output of
the fourth microphone unit, and the output of the first inversion circuit What is characterized by
comprising a third addition circuit for adding each and a fourth addition circuit for adding the
output of the attenuation circuit, the output of the fifth microphone unit, and the output of the
second inversion circuit. It is.
[0008]
Also, the invention of claim 2 of the present application is the first microphone unit whose
directivity characteristic is non-directional, is disposed with the central axis shifted substantially
180 degrees, and the directivity characteristic has characteristics of bi-directionality,
respectively. Surround microphone unit including second and third microphone units for
outputting audio signals in the directional direction, an attenuation circuit for attenuating the
output of the first microphone unit, and output in one directional direction of the second
microphone unit A second inverting circuit that inverts the output of the second microphone unit
in the other pointing direction, and a third that inverts the output of the third microphone unit in
the other pointing direction An inverting circuit, a fourth inverting circuit for inverting the output
of the third microphone unit in the other pointing direction, an output of the attenuation circuit,
one of the second microphone units, The first addition circuit adds the outputs of the other
pointing direction, the second addition circuit adds the output of the attenuation circuit, the
output of one of the third microphone units and the output of the other pointing direction, and
the attenuation circuit The output of the first inverting circuit, the output of the first inverting
circuit, the output of the second inverting circuit, the output of the attenuating circuit, the output
of the third inverting circuit, and the output of the fourth inverting circuit And a fourth addition
circuit for adding.
[0009]
In operation, a surround microphone unit is disposed in space, in which the nondirectional first
microphone unit and the second to fifth microphone units having directional characteristics are
disposed with their central axes shifted by 90 degrees.
When sound is emitted from any place in space, each microphone unit of the surround
microphone unit outputs an electrical signal of amplitude based on its directivity characteristic.
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The first addition circuit adds the output of the attenuation circuit and the forward and reverse
outputs of the microphone unit directed forward and backward, respectively.
The second addition circuit adds the output of the attenuation circuit and the inverted output and
the non-inverted output of the left and right microphone units. The third summing circuit adds
the output of the attenuating circuit and the inverted and the non-inverted output of the front
and back of the Marochromon unit. The fourth addition circuit adds the output of the attenuation
circuit and the forward and reverse outputs of the left and right microphone units. The audio
outputs of the first to fourth addition circuits are output as surround signals of four channels.
[0010]
A surround microphone system according to a first embodiment of the present invention will be
described below with reference to the drawings. FIG. 1 is a block diagram showing the
configuration of a surround microphone system according to a first embodiment of the present
invention. A surround microphone unit 10 is installed at a position separated by a distance D
from a sound source 1 to be recorded. FIG. 2 is a perspective view showing the appearance of the
surround microphone unit 10. As shown in FIG. 2, the first microphone unit 11 with no
directivity, the second microphone unit 12 with a single directivity, the third microphone unit 13,
the fourth microphone unit 14, the fifth The microphone units 15 are arranged, for example, on a
straight line perpendicular to the floor surface. As shown in the figure, the omnidirectional
microphone unit 11 is disposed, for example, in the center, and the unidirectional axes of the
second to fifth microphone units 12 to 15 are arranged so that their central axes rotate by 90
degrees. The middle axis of the pointing direction of the second and third microphone units 12
and 13 is the front direction.
[0011]
Sound waves W1 to W5 emitted by the omnidirectional microphone unit 11 and the
unidirectional microphone units 12 to 15 in FIG. 1 are converted into electric signals S3 to S7,
respectively. The signal S3 of the microphone unit 11 is given to the attenuation circuit 20. The
attenuation circuit 20 is a circuit that attenuates the signal S3, and its attenuation rate is, for
example, 1/5. The outputs S4 to S7 of the second to fifth microphone units 12 to 15 are given to
the first to fourth inverting circuits 21 to 24, respectively. The inverting circuits 21 to 24 are
circuits for inverting the signals S4 to S7, respectively. The adder circuits 25 to 28 are adder
circuits that add the signals of three inputs and normalize them so that the maximum amplitude
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becomes one. The addition circuit 25 adds the output of the attenuation circuit 20, the signal S4
and the inverted signal of the signal S6. The addition circuit 26 adds the output of the
attenuation circuit 20, the signal S5, and the inverted signal of the signal S7. The addition circuit
27 adds the output of the attenuation circuit 20, the signal S6, and the inverted signal of the
signal S4. The addition circuit 28 adds the output of the attenuation circuit 20, the signal S7, and
the inverted signal of the signal S5. These addition signals are output as surround sound signals
of four channels via the output terminals 29-32.
[0012]
FIG. 3 is a pattern diagram showing directivity characteristics of the surround microphone unit
10. As shown in FIG. As shown in the drawing, assuming that the arrow Y1 direction is the front
direction and the arrow Y2 direction is θ = 0 degrees, the directivity characteristic of the
microphone unit 12 becomes a cardioid indicated by the solid line P1. The directivity
characteristic of the microphone unit 13 is a cardioid indicated by a broken line P2. Likewise, the
directivity characteristics of the microphone units 14 and 15 are the solid line P3 and the broken
line P4, respectively.
[0013]
The operation of the surround microphone system configured as described above will be
described. FIG. 4 changes the sound pressure radiated from the speakers disposed on the left and
right, respectively, and the sense of localization of the sound felt by the viewer is represented by
a normal viewing room (shown by a solid line) and an anechoic room (shown by a broken line) It
is a figure which shows the position of the investigated sound image. This is reported in the
following document. H. D. Harwood “Stereo Image Sharpness” Wireless World July 1968
[0014]
Here, speakers are placed at two vertices of an equilateral triangle having a length of 1 at one
side, and the viewer at the other vertex estimates the position of the sound source by ear. For
example, when sound is produced by increasing the volume from the left speaker, the position of
the sound source is considered to be at the left position from the central axis. To the left When
viewed as 0.5 (left speaker), the sound pressure difference between the left and right speakers is
about 18 to 19 dB. When sound at the same level is emitted from the left and right speakers, the
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position of the sound source is considered to be at the center (0), and the sound pressure
difference between the left and right speakers is 0 dB.
[0015]
As known from FIG. 4, the positional relationship of the sound image due to the level difference
of the sound emitted from the two speakers is determined almost regardless of the acoustic
condition of the room reproducing the sound. Therefore, after a plurality of audio signals
collected using the surround microphone unit 10 are once recorded by the recording device,
these audio signals are amplified again and reproduced from a plurality of speakers in a normal
viewing room. If the relationship between the level difference between the microphone units that
make up the sound source and the position of the sound image is designed to match the
characteristics shown in FIG.
[0016]
Now, in FIG. 3, the curve of the cardioid whose directivity characteristic is the curve P1 is
expressed as (1 + cos θ) / 2, where θ = 0 in the direction of the arrow Y2. Moreover, the
cardioid of the curve P3 of this directivity characteristic and 180-degree rotational symmetry is
expressed as (1-cos (-θ)) / 2. Therefore, in FIG. 1, when the signal S4 from the microphone unit
12 having the directivity of the curve P1 and the signal S6 inverted from the microphone unit 14
having the directivity of the curve P3 are added by the adder 25, [(1+ cos θ ] / 2- (1-cos (.theta.)) / 2] = (cos .theta.) / 2 + (cos (-.theta.)) / 2 = cos .theta., Which is identical to the directivity
characteristic (cos .theta.) Of bi-directionality.
[0017]
Similarly, when a signal S5 from the microphone unit 13 having the directivity of the curve P2
and a signal obtained by inverting the signal S7 from the microphone unit 15 having the
directivity of the curve P4 are added by the adder 26, sin θ is obtained. This is the same as the
case of rotating the cos θ by 90 degrees.
[0018]
The directivity characteristic of the target shown in FIG. 4 can be obtained by changing and
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adding the ratio of these output signals using a bi-directional microphone unit and a nondirectional microphone unit.
For example, there are known Pi-Park geoids whose directional characteristics are curves of (1 +
3 cos θ) / 4, supercardioids whose curves of directional characteristics are (0.37 + 0.63 cos θ),
and the like.
[0019]
Using the surround microphone system of the present embodiment shown in FIGS. 1 and 2, the
characteristics in the case of collecting a sound source present in any part of 360 degrees in
space are analyzed. FIG. 5 is a characteristic diagram showing left and right sound pressure level
differences input to each microphone unit when the position of a sound source (sound image) is
changed in each surround microphone system having each directivity characteristic described
above. In the figure, a solid line A is a copy of the curve of FIG. 4 and is a curve showing an ideal
sound pressure level difference with respect to the sound source position in a normal viewing
room.
[0020]
FIG. 6A is calculation data showing the sound image position (angle) and the sound pressure level
difference between the left and right of the bi-directional microphone which draws a curve of cos
θ, and when it is plotted in FIG. The curve B is much more directional than the curve A. For
example, when the sound source moves 35 degrees from the central axis, it gives the viewer an
illusion as if the sound source moved 42 degrees. FIG. 6 (b) is calculated data in the case of the
Pi-Parker geoid that draws a curve of (1 + 3 cos θ) / 4, and when this is plotted, the curve C of
FIG. 5 is obtained. Further, FIG. 7 (a) is calculation data in the case of a cardioid which draws a
curve of (1 + cos θ) / 2, and when this is plotted, it becomes a broken line D of FIG. Curves C and
D in FIG. 5 show that the amount of movement of the sound felt by the viewer is smaller than the
actual amount even if the actual sound source moves, which is insufficient as the characteristics
of the surround sound system.
[0021]
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Therefore, as a result of assuming various conditional expressions to obtain the curve A in FIG. 5,
it was found that when the directional characteristic draws a curve of (1 + 5 cos θ) / 6, it is
extremely consistent with the target characteristic. FIG. 7 (b) is calculated data in the case of
drawing a curve of (1 + 5 cos θ) / 6, and when this is plotted, it becomes curve E of FIG. In this
figure, it can be seen that the target characteristic A and the characteristic E of the present
embodiment are almost equal. That is, the ratio of each output signal of the nondirectional
microphone unit 11 input to the attenuation circuit 20 of FIG. 1 and the bidirectional
microphone unit input to each of the adding circuits 25 to 28 is 1: 5. The reason is that weighted
averaging is performed in each addition circuit.
[0022]
Further, the inverting circuits 21-24 invert the outputs of the microphone units 12-15, which are
the directivity characteristics of the cardioid, so that the added values of the adding circuits 2528 become bi-directional characteristics. The outputs of the adding circuits 25 to 28 serve to
realize the target directivity characteristic (1 + 5 cos θ) / 6. In the above equation, although the
arrow Y2 direction shown in FIG. 3 is θ = 0, assuming that the Y1 direction is the reference
direction of the surround microphone unit 10, the directivity characteristic of the target is (1 + 5
cos (θ ± 45)) / It goes without saying that it becomes six.
[0023]
FIG. 8 is a curve showing the overall directivity characteristic of the surround microphone system
in the present embodiment. As shown in the figure, the omnidirectional microphone unit 11
installed at the center O of the space including the sound source and the microphone units 12 to
15 having directivity of four cardioids on a straight line perpendicular to the floor surface The
directional characteristics in the case of installation are shown by four solid lines.
[0024]
FIG. 9 is a block diagram showing the configuration of a surround microphone system according
to a second embodiment of the present invention. As in the first embodiment, the attenuation
circuit 20, the inversion circuits 21 to 24, and the addition circuits 25 to 28 are provided in the
figure. The sound waves W1 to W3 emitted from the sound source 1 in space are given to the
nondirectional first microphone unit 11 and the second and third microphone units 41 and 42 of
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the bi-directional characteristic. Unlike the first embodiment, the microphone units 41 and 42 do
not combine the outputs of the two cardioid characteristic microphone units to realize bidirectional characteristics, but are microphone units having characteristics of bi-directional
characteristics alone. is there.
[0025]
The microphone units 41 and 42 output audio signals in bidirectional directivity directions, and
the front and rear signals of the microphone unit 41 are applied to the addition circuit 25 and to
the inversion circuits 21 and 22, respectively. . Similarly, the left and right signals of the
microphone unit 42 are applied to the addition circuit 25 and to the inversion circuits 23 and 24,
respectively. The adder circuit 25 adds the output of the attenuation circuit 20 and the front
signal and the rear signal of the microphone unit 41, respectively. The adder circuit 26 adds the
output of the attenuation circuit 20, the left signal and the right signal of the microphone unit
42, respectively. The adder circuit 27 adds the output of the attenuation circuit 20 and the
outputs of the inverting circuits 21 and 22, respectively. The adder circuit 28 adds the output of
the attenuation circuit 20 and the outputs of the inverting circuits 23 and 24, respectively. These
addition signals are output as surround sound signals of four channels via the output terminals
29-32.
[0026]
The operation of the surround microphone system configured as described above is the same as
that of the first embodiment, and thus the description thereof is omitted. Although the output
signals of the first and second embodiments are four channels, it goes without saying that
recording can be performed on a two-channel recording medium by processing such as Dolby
encoding. Also, if the 4 channel surround signal processed in this way is recorded in a recording
device such as a magnetic recording / reproducing device, the localization feeling of the original
sound is impaired from the speakers provided at the four corners of the viewing room or
ordinary room during reproduction. Sound is faithfully reproduced without.
[0027]
As described above, according to the present invention, when the direction range of the sound
source to be recorded is 360 degrees including the front and back, the directivity characteristics
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in which the nondirectional microphone unit intersects each other at a specific angle are By
using a plurality of sets of microphone units, it is possible to realize an excellent surround
microphone system that faithfully outputs an audio signal of four channels in a space including a
sound source. Further, by reproducing the sound recorded by the surround microphone system
by the speakers provided at different positions in the space, it is possible to reproduce the sound
excellent in the sense of reality and the sense of localization.
[0028]
Brief description of the drawings
[0029]
1 is a block diagram showing the configuration of a surround microphone system according to a
first embodiment of the present invention.
[0030]
2 is a perspective view showing the appearance of the surround microphone unit in the present
embodiment.
[0031]
3 is an explanatory view showing directivity characteristics of the surround microphone unit in
the present embodiment.
[0032]
42 is a characteristic diagram showing the relationship between the sound pressure level
difference between the speakers and the position of the sound image.
[0033]
FIG. 52 is a characteristic diagram showing the relationship between the sound pressure level
difference between the microphone units and the position of the sound image.
[0034]
FIG. 6 (a) is a characteristic table of the bidirectional microphone unit, and FIG. 6 (b) is a
characteristic table of the pi-Parker geoid directional microphone unit.
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[0035]
FIG. 7A is a characteristic table of the cardioid directional microphone unit, and FIG. 7B is a
characteristic table of the directional microphone unit of this embodiment.
[0036]
8 is a diagram showing the directivity characteristics of the surround microphone unit of the
present embodiment.
[0037]
9 is a block diagram showing the configuration of a surround microphone system according to a
second embodiment of the present invention.
[0038]
10 is an explanatory view showing the arrangement of the conventional stereo microphone unit.
[0039]
FIG. 11 is an explanatory view showing directivity characteristics of the conventional stereo
microphone unit.
[0040]
Explanation of sign
[0041]
Reference Signs List 1 sound source 10 surround microphone unit 11 omnidirectional
microphone unit 12 to 15 unidirectional microphone unit 20 attenuation circuit 21 to 24
inverting circuit 25 to 28 addition circuit 29 to 32 output terminal 41, 42 bidirectional
microphone unit
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