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JPH05191887

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Notice
This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JPH05191887
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention 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
audiovisual equipment.
[0002]
2. Description of the Related Art A conventional stereo microphone system will be described. FIG.
4 is an explanatory view showing directivity characteristics of a stereo microphone unit usually
called an MS microphone. In the figure, the stereo microphone unit is installed at the center
position of the space including the sound source. In this microphone unit, two types of
microphones are provided at positions perpendicular to the floor surface, and the first and
second microphones 1 and 2 are disposed such that the central axes at which the sound pressure
sensitivity is maximum are mutually orthogonal. It is done. Assuming that the arrow Y direction
is the front, the first microphone 1 directed in this direction is a microphone having a directional
sensitivity characteristic which is a curve of cardioid as indicated by a solid line.
[0003]
On the other hand, the second microphone 2 is a bi-directional (bi-directional) microphone
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having directivity characteristics in + X and ?X directions as indicated by a broken line. The
stereo microphone system has an arithmetic circuit for processing the output signals of the first
and second microphones 1 and 2, and the signal M collected by the first microphone 1 and the
signal M collected by the second microphone 2 The sounded two-channel signals + S and -S are
respectively added by an arithmetic circuit to obtain a left channel output signal (M + S) and a
right channel output signal (M-S).
[0004]
This MS microphone is described in detail in the following paper. WLDooley and RDStreicher,
"MS Stereo: A Powerful Technique for Working in Stereo," JAES Vol. 30, 1982 Oct p 707-718
Then, the 2-channel signal collected by this MS microphone is indoors at an opening angle of 90
degrees. In the case of reproduction with two speakers arranged in front of the sound image
localization direction is as shown in FIG.
[0005]
FIG. 5 is a view showing the position of a sound image in which the sense of localization of the
sound felt by the viewer is examined in the viewing room by changing the sound pressure
radiated from the speakers disposed on the left and right, respectively. The horizontal axis
indicates the direction (angle) of the sound image or the sound source, and the vertical axis
indicates the sound pressure level difference between the two channels. This is reported in the
following document. H. D. Harwood, "Stereophonic Image Sharpness" Wireless World, July 1968,
p207-211
[0006]
Curve A represents the level difference between the two channels when the direction of the
sound source is changed. For example, speakers are placed at two vertices of a right-angled
isosceles triangle, and a viewer at the right-angled vertex estimates the position of the sound
source by ear. For example, if the volume of the left speaker is increased to produce sound, the
position of the sound source is perceived as being to the left of the central axis. The sound
pressure difference between the left and right when perceived as being at 45 degrees to the left
is about 18 to 19 dB. When sound of the same level is emitted from the left and right speakers,
the position of the sound source is considered to be at the center (0 degree), and the sound
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pressure difference between the left and right becomes 0 dB.
[0007]
Curve B, on the other hand, shows the relationship between the localization direction of the
sound image and the level difference between the two-channel output of the MS microphone
when the direction of the sound source is changed and this sound is collected by the MS
microphone. In this data, assuming that the arrow Y direction is ? = 0 in FIG. 4, the equation
representing the directivity characteristic of the first microphone 1 is (1 + cos ?) / 2, and the
arrow X direction is ? ? = 0. The equation representing the directivity characteristic of the
second microphone 2 is sin ? ?, which is the result of calculation using this equation. As can be
seen from FIG. 5, the curves A and B are substantially similar, and it can be said that the sound
source direction can be faithfully reproduced when sound is collected by such an MS
microphone.
[0008]
However, in the microphone unit having such a configuration, the first microphone 1 whose
directivity characteristic becomes a cardioid is disposed so that the central axis direction is in the
front direction, and the directivity characteristic is bidirectional. The second microphone 2 is
disposed so that the central axis direction is at right angles to the front, so that there is a
disadvantage that the sound collection range is limited to the front. Also, the bidirectional
microphone 2 has a disadvantage that its structure is complicated and its productivity is inferior.
[0009]
The present invention has been made in view of such conventional problems, and it is an object
of the present invention to realize an inexpensive surround microphone system which can be
realized with a simple configuration and is excellent in productivity.
[0010]
SUMMARY OF THE INVENTION The present invention is a surround microphone including first
to fourth microphone units, each of which includes first to fourth microphone units whose
directional characteristics draw a cardioid curve and are shifted by substantially 90 degrees from
each other by central axes. , First to fourth attenuation circuits that respectively attenuate the
outputs of the first to fourth microphone units, first to fourth inverting circuits that respectively
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invert the outputs of the first to fourth attenuation circuits, and A first addition circuit that adds
the output of the second inversion circuit and the output of the first microphone unit; a second
addition circuit that adds the output of the first inversion circuit and the output of the second
microphone unit; A third addition circuit that adds the output of the fourth inversion circuit and
the output of the third microphone unit; and a fourth addition circuit that adds the output of the
third inversion circuit and the output of the fourth microphone unit Tool It is characterized in
that.
[0011]
In operation, surround microphones in which first to fourth microphone units having cardioid
directional characteristics are disposed with their central axes mutually offset by 90 degrees are
installed in a space.
When sound is emitted from any place in space, each microphone unit of the surround
microphones outputs an electrical signal of amplitude based on its directivity characteristic.
These signals are attenuated by the respective attenuation circuits and given to the first to fourth
inverting circuits. The first adder circuit adds the output of the second inverter circuit and the
output of the first microphone unit, and the second adder circuit adds the output of the first
inverter circuit and the output of the second microphone unit, The third addition circuit adds the
output of the fourth inversion circuit and the output of the third microphone unit, and the fourth
addition circuit adds the output of the third inversion circuit and the output of the fourth
microphone unit. Then, the audio output of the first to fourth addition circuits is output as a
surround signal, and recorded on a 4-channel recording medium.
[0012]
A surround microphone system according to an 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 an embodiment of the present
invention. In the figure, the surround microphone unit 10 is installed at a position apart from the
sound source 9 to be recorded. FIG. 2 is a perspective view showing the appearance of the
surround microphone unit 10. As shown in the figure, the first microphone unit 11, the second
microphone unit 12, the third microphone unit 13, and the fourth microphone unit 14 whose
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directivity characteristics are cardioid are respectively perpendicular to the floor surface. It is
arranged on the same straight line. The first to fourth microphone units 11 to 14 are arranged so
that their central axes rotate by 90 degrees, and the intermediate axes of the first and second
microphone units 11 and 12 are in the front direction.
[0013]
In FIG. 1, sound waves W1 and W2 emitted from a sound source 9 are picked up by the first to
fourth microphone units 11 to 14 and converted into electric signals S1, S2, S3 and S4,
respectively. These signals S1 to S4 are given to first to fourth attenuation circuits 15 to 18,
respectively. Attenuating circuits 15 to 18 are circuits for attenuating the signals S1 to S4,
respectively, and their attenuation rate is G. The outputs of attenuation circuits 15-18 are applied
to first through fourth inverting circuits 19-22. The inverting circuits 19-22 invert the outputs of
the attenuation circuits 15-18, respectively.
[0014]
On the other hand, the adder circuits 23 to 26 are circuits for adding two input signals,
respectively. The first addition circuit 23 adds the output of the second inversion circuit 20 and
the signal S1 of the first microphone unit 11. The second addition circuit 24 adds the output of
the first inversion circuit 19 and the signal S2 of the second microphone unit 12. The third
addition circuit 25 adds the output of the fourth inversion circuit 22 and the signal S3 of the
third microphone unit 13. The fourth addition circuit 26 adds the output of the third inversion
circuit 21 and the signal S4 of the fourth microphone unit 14. The addition signals of the
addition circuits 23 to 26 are output as surround sound signals of four channels from the output
terminals 27 to 30, respectively.
[0015]
Now, the opening angle 2? between the microphone units whose directivity characteristic is the
cardioid, and the attenuation factor G of the attenuation circuit will be described. Assuming that
the angle of the sound source with respect to the front direction of the surround microphone unit
10 shown in FIG. 2 is ?, and the opening angle of the first and second microphone units 11 and
12 is 2?, the first microphone 11 directed to the front right The directivity characteristic DR (?)
and the directivity characteristic DL (?) of the second microphone unit 12 directed to the front
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left side are expressed by the following equations (1) and (2). DR (?) = (1 + cos (? + ?)) / 2 и и и
(1) DL (?) = (1 + cos (?-?)) / 2 и и и (2)
[0016]
Accordingly, in FIG. 1, the front left channel output signal EL (.theta.) Output from the output end
28 of the surround microphone system is expressed by the following equation (3). EL (?) = (1 +
cos (?-?)) / 2 + G О (1 + cos (? + ?)) / 2 иии (3) Similarly, the front right channel output signal
ER (?) output from the output end 27 is It becomes the following (4) formula. ER (?) = (1 + cos
(? + ?)) / 2 + G О (1 + cos (?-?)) / 2 и и и (4) Also, the rear left channel output signal output
from the output end 29 of the surround microphone system The rear right channel output signal
output from the end 30 is also expressed by the same equation in consideration of the central
axis in the direction opposite to the front of FIG.
[0017]
Here, when the sound source angle ? is changed from 0 to 45 degrees, a curve obtained
corresponding to the specific opening angle 2? of the microphone units 11 and 12 and the
attenuation factor G of each attenuation circuit is a curve A of FIG. It should be decided to
approximate to When the sound source 9 in any direction is picked up by the four microphone
units 11 to 14, the opening angles of the microphone units 11 to 14 may be equally spaced, so
the opening angle 2? is 90 degrees. . Therefore, it was found that the value of G is 1/3 when the
value of ? is fixed at 45 degrees and the optimum attenuation factor G is determined.
[0018]
That is, the signals output from the output terminals 28 and 27 are expressed by the following
equations (5) and (6). EL (?) = (1 + cos (??45)) / 2 + 1/3 О (1 + cos (? + 45)) / 2... (5) ER (?)
= (1 + cos (? + 45)) / 2 + 1/3 О (1 + cos () ?-45)) 2 и и и (6)
[0019]
Based on the equations (5) and (6), the characteristics of the level difference between the audio
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signals input to the left and right speakers (not shown) and the position (angle) of the sound
image become a curve C in FIG. The result is very similar to the curve A in which the ideal curve
is transferred to FIG. Therefore, it can be said that the direction of the sound image can be
faithfully reproduced.
[0020]
The two human ears are on the left and right, and the localization ability in the sound image
direction is better in the left and right direction than in the front and back direction. The
characteristic of FIG. 3 shows the relationship between the sound pressure level difference
between the left and right channels, which is one plane of human hearing ability, and the
localization direction of the sound image, but the condition is the left and right direction in the
front. That is, when divided by the area of 90 degrees by the central axis of the directivity
characteristic of four microphone units of 360 degrees, the section of the area enclosed by 45
degrees to the left of the front and the range surrounded by 135 degrees to the left of the rear
There is no practical problem when considering only the section of.
[0021]
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 characteristic is
a cardioid and the directions are changed by 90 degrees each other. By using the surround
microphone unit configured by the provided first to fourth microphone units, it is possible to
realize a surround microphone system for obtaining 4-channel audio signals capable of faithfully
reproducing a spatial sound image including a sound source. In addition, since only the
microphone unit of the cardioid directivity characteristic is used, the configuration is simplified,
and an inexpensive surround microphone system with excellent productivity can be realized. 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.
[0022]
Brief description of the drawings
[0023]
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1 is a block diagram showing the configuration of a surround microphone system in the
embodiment of the present invention.
[0024]
2 is a perspective view showing the appearance of the surround microphone unit in the present
embodiment.
[0025]
3 is a characteristic diagram showing the relationship between the sound pressure level
difference between the two microphone units in the present embodiment and the position of the
sound image.
[0026]
4 is an explanatory view showing the directional characteristics of the conventional stereo
microphone unit.
[0027]
5 is a characteristic diagram showing the relationship between the sound pressure level
difference and the position of the sound image in the conventional stereo microphone unit.
[0028]
Explanation of sign
[0029]
9 sound source 10 surround microphone unit 11 first microphone unit 12 second microphone
unit 13 third microphone unit 14 fourth microphone unit 15 to 18 first to fourth attenuation
circuits 19 to 22 first to fourth Inversion circuit 23 first addition circuit 24 second addition
circuit 25 third addition circuit 26 fourth addition circuit 27 to 30 output terminal
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