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JPH0775195

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DESCRIPTION JPH0775195
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
MS stereo microphone, and more particularly to an MS stereo microphone mounted on a video
camera.
[0002]
2. Description of the Related Art A one-point stereo sound collection microphone is classified into
a pair microphone system and a coaxial system. In the pair microphone system, two microphones
having the same characteristic are disposed at an appropriate distance, and an opening angle
between the main axes of the two microphones becomes an appropriate size, and the levels of the
two microphone outputs are obtained. The difference and the phase difference can be used as
direction information of the sound source. On the other hand, in the coaxial method, two
directional microphones having the same characteristic are disposed at the same position, and
the direction is set so that the opening angle formed by the main axes of the two microphones
becomes about 90 to 120 °. Only the level difference between the outputs of the two
microphones is used as direction information of the sound source.
[0003]
In the case of the pair microphone system, if the installation of two microphones is optimum, it is
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possible to perform excellent stereo sound collection that can not be obtained by the coaxial
system, but the distance between the two microphones and the direction of the main axis are to
be collected Fine adjustments are required according to the acoustic characteristics of the sound
source and the recording site, and coaxial microphones are often used in terms of ease and
reproducibility. In the coaxial method, two methods of MS method and XY method are used.
[0004]
FIG. 7 shows an example of the configuration of a conventional MS system stereo microphone. As
shown, the unidirectional microphone M (mid) microphone 1 and the bidirectional S (side)
microphone 2 are disposed close to each other so that their directional axes are orthogonal to
each other. A microphone that generates a sum signal and a difference signal of the two outputs.
Reference numerals 3 and 4 in the figure denote adders. FIG. 8 shows a directivity pattern in
which the main axis direction of the M microphone 1 of the MS type microphone configured as
shown in FIG. 7 is 0 degree. One scale indicated by the concentric circles is 10 dB. In FIG. 8, 5
indicates the directivity of the M microphone 1 and 6 indicates the directivity of the S
microphone 2. The polarity of the output of the S microphone 2 is + for sound waves coming
from the hemisphere on the main axis (-90 degrees) side. It becomes-on the opposite (90
degrees) side. Therefore, assuming that the polarity of M microphone 1 is +, the directivity of the
signal obtained by adding the outputs of M microphone 1 and S microphone 2 is 7, and the
directivity of the signal obtained by subtracting the output of S microphone 2 from the output of
M microphone 1 It looks like 8 Therefore, it is possible to obtain stereo two-channel signals to
the left of the output of the adder 3 of FIG. 7 and to the right of the output of the adder 4.
[0005]
In the XY method, two single directional microphones having directivity as shown in FIG. 8 are
disposed close to each other so that an angle formed by each main axis is 90 to 120 °. It is a
system. Since the coaxial stereo microphone is a microphone that uses only the level difference
between the outputs of the two microphones as information regarding the direction of the sound
source, it is necessary to place the two microphones at one point in space. However, in the XY
method, since two unidirectional microphones are used, it is possible to arrange them close to
each other, but it is impossible to arrange the two microphones at one point completely, and it is
purely You can not retrieve only the level difference. In the case of one MS method, M
microphones and S microphones are disposed close to each other in the vertical direction, and a
sum signal and a difference signal of the both are generated, as shown in 7 and 8 of FIG. Two
microphones are arranged at one point in the horizontal plane, and a stereo microphone with
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only a level difference can be configured completely.
[0006]
Therefore, MS stereo microphones are superior in localization of the reproduced sound image
because only the level difference is used as direction information, and by adjusting the sensitivity
of the S microphone, the directivity pattern and the maximum of the left and right channels are
obtained. Since the opening angle in the direction of sensitivity can be changed, the stereo
microphones of the coaxial method compared with the XY method, such as the reverberation
characteristics of the recording site, and the ease of adjustment considering the size and the
spread of the reproduced sound image. As an advantage is great.
[0007]
However, in the MS stereo microphone configured as described above, if there is an obstacle that
disturbs the sound field around the individual microphone units, the reflection of the sound wave
by the obstacle will be reflected. The characteristics of each microphone unit are disturbed by
diffraction, and even if the outputs of the two microphones are combined, it is not possible to
obtain a good directivity pattern inherent to the MS method as shown in FIG.
Therefore, in order to mount the conventional MS microphone in the video camera, the
microphone is disposed sufficiently spatially separated from the housing so that the microphone
is not affected by the reflection or diffraction of the sound wave by the housing of the video
camera. There is a need. In addition, since it is necessary to arrange the M microphones and the S
microphones in the vertical direction as described above, the space required in the vertical
direction for the microphones becomes large. For the above reasons, there is a problem that the
video camera can not be miniaturized if the conventional MS type microphone is built in a
housing.
[0008]
Generally, MS microphones are primary sound pressure gradient type microphones, but sound
pressure gradient microphones basically have low sound pressure sensitivity in the main axis
direction in the low frequency range, so the frequency is flat up to the low frequency range It is
more susceptible to wind noise and vibration noise than non-directional microphones with
characteristics. Therefore, when the conventional MS microphone is incorporated in a small
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video camera, the sound collection SN ratio in the low frequency range is lowered by the
vibration emitted by the mechanical system inside the case and by the wind when used outdoors.
There was a point.
[0009]
In the MS method, the sensitivity adjustment of the S microphone can change the opening angle
in the direction of maximum sensitivity of the left and right channels, but in the case of the
conventional MS method, such sensitivity adjustment is performed within the fine adjustment
range. There has been a problem that it is impossible to realize an acoustic zoom effect that
emphasizes the sound emitted by the subject in the front direction in synchronization with the
change in the angle of view of the optical system of the video camera.
[0010]
The microphone for a video camera according to the present invention solves the abovementioned problems and can maintain good characteristics as a stereo microphone even when
incorporated in a video camera housing, and sound collection by vibration or wind generated by
a mechanical system An object of the present invention is to provide a stereo microphone for an
MS system video camera having an acoustic zoom function which is less likely to cause a
decrease in the SN ratio and which is adapted to the zooming of an image.
[0011]
[Means for Solving the Problems] In order to achieve the above object, the stereo microphone for
video camera of the present invention uses four nondirectional microphone units and arranges
them so as to be located at each vertex of a square. An M microphone is formed by using a pair
of units at both ends of one diagonal of a square, and an S microphone is formed by electrical
signal processing using a pair of units at both ends of the other diagonal.
[0012]
In addition, among the frequency regions to be collected, a low frequency region is provided with
a region in which the directivity in the final output is nondirectional.
Further, the gain of the output of the S microphone is made variable in the range of 0 or more
and 2 or less according to the zoom control signal of the optical system.
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[0013]
The stereo microphone for video camera according to the present invention having the above
configuration receives sound using four nondirectional microphone units arranged in a plane,
and performs electrical signal processing on the output of each microphone unit. Since four
microphone units can be arranged on the top or bottom of the video camera housing, the system
can obtain desired directivity.
Since the sound pressure distribution is not affected by the reflection and diffraction of the object
only in the plane constituting the outer shape of the object placed in the free sound field and on
the plane parallel to the traveling direction of the sound wave, By attaching it to the top or
bottom of the case, it is possible to maintain the original directivity of the MS method shown in
FIG. 8 for the sound source located at least in the horizontal plane including the video camera.
In addition, since the four nondirectional microphone units are located at the apex of the square,
two apparent microphones for the left and right channels formed by electrical signal processing
can be arranged at one point in the same horizontal plane. .
[0014]
In addition, by making the low frequency region nondirectional, it is possible to prevent the
decrease in sound pressure sensitivity in the low frequency region, so the sound pickup SN ratio
due to wind noise with low power and vibration noise with low frequency Can be reduced.
[0015]
In addition, by making the gain of the output of the S microphone variable in the range of 0 or
more and 2 or less, the direction from the state of the stereo microphone by MS method to the
state of maximum sensitivity in the microphone front (video camera front) direction is
continuously directed. It is possible to change the nature and realize the acoustic zooming effect.
[0016]
Examples of the present invention will be described in detail below.
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FIG. 1 is a diagram showing the configuration of a first embodiment of the stereo microphone for
video camera of the present invention.
In FIG. 1, 9, 10, 11, and 12 are all nondirectional microphone units, and are disposed so as to be
located at each vertex of a square of an appropriate size. The output of the microphone unit 10 is
input to the delay unit 13. The delay time τ of the delay unit 13 is given by τ = d / c, where d is
the distance between the microphone 9 and the microphone unit 10 and c is the speed of sound.
The adder 14 subtracts the output of the delay unit 13 from the output of the microphone unit 9.
The directivity pattern at the output of the adder 14 is the same pattern as 5 in FIG. 8, and the
output of the adder 14 corresponds to the output of the unidirectional M microphone. The adder
15 outputs a difference signal between the output of the microphone unit 11 and the output of
the microphone unit 12. The directivity pattern at this output is the same as 6 in FIG. 8, and the
output of the adder 15 is bidirectional. It corresponds to the output of the S microphone. The
output of the adder 15 is amplified by an amplifier 16. The adder 17 and the adder 18
respectively output a sum signal and a difference signal of the output of the amplifier 16 and the
output of the adder 14. In the final output of the stereo microphone configured as shown in FIG.
1, assuming that the gain of the amplifier 16 is 2, directivity patterns shown in 7 and 8 of FIG. 8
can be obtained.
[0017]
Since the center of the primary sound pressure gradient microphone can be viewed as the middle
point of two sound reception points, in the stereo microphone for a video camera in this
embodiment, both the M microphone and the S microphone formed by signal processing are
used. It will be located at the center of the square formed by the four nondirectional microphone
units 9-13. Therefore, the apparent two microphone positions obtained by combining the outputs
of the M and S microphones also become the center of the square, and a stereo microphone can
be configured completely by only the level difference. Furthermore, there is no deterioration of
directivity due to the influence of reflection and diffraction of the casing, and it becomes possible
to maintain good characteristics as a MS-type stereo microphone while being incorporated in the
casing.
[0018]
FIG. 2 is a view showing the configuration of a second embodiment of the microphone for video
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camera of the present invention. The difference from the first embodiment is that the low
frequency component of the output of the first microphone unit 19 is removed by the high pass
filter 23 and then input to the adder 25. The other configuration is all shown in FIG. This is
similar to the first embodiment. In the figure, 20 is a second microphone unit, 21 is a third
microphone unit, 22 is a fourth microphone unit, 24 is a delay unit, 26 is an adder, 27 is an
amplifier, and 28 and 29 are adders.
[0019]
The directivity at the output of the adder 25 of the microphone configured in this way is nondirectivity in the low frequency band and uni-directional in the high frequency band with the
cutoff frequency of the high pass filter 23 as the boundary.
[0020]
When the distance between the first microphone unit 19 and the second microphone unit 20 and
the distance between the third microphone unit 21 and the fourth microphone unit 22 in FIG. 3
are 10 mm, and the cutoff frequency of the high pass filter 23 is 200 Hz. 12 shows the directivity
pattern of the final output (left channel) of the microphone of the present embodiment.
In the figure, 30 is a directivity pattern when the frequency is 100 Hz and 31 is a directivity
pattern when the frequency is 2 kHz. In the final output, the directivity pattern of the MS system
can be obtained in almost the same manner as in the first embodiment in the high frequency
range, but it becomes nondirectional in the low frequency range.
[0021]
Therefore, in the microphone of the present embodiment, since the sound pressure sensitivity
does not decrease in the low frequency range, the decrease in sound pickup SN ratio due to wind
noise and low frequency vibration noise is similar to that of the nondirectional microphone. It is
possible to maintain a higher sound collection SN ratio than that of the MS type microphone.
[0022]
FIG. 4 is a view showing the configuration of a third embodiment of the stereo microphone for
video camera of the present invention.
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The difference from the first embodiment is that the gain of an amplifier 39 for amplifying the
output of the adder 38 can be varied, and all other configurations are similar to those of the first
embodiment shown in FIG. . In the figure, reference numerals 32, 33, 34 and 35 denote
microphone units, 36 denotes a delay unit, and 37, 38, 40 and 41 denote adders.
[0023]
The gain of the amplifier 39 is determined according to the zoom control signal of the optical
system. When the angle of view of the image is widest, the gain is set to 2, and as the angle of
field narrows, the gain decreases. When the angle of view is narrowest, the gain is set to 0. FIG. 5
shows the directivity pattern of the final output of the microphone of this embodiment. In the
figure, reference numerals 42 and 43 respectively denote left channel and right channel
directivity patterns when the gain of the amplifier 39 is 2 (maximum angle of view), and 44 and
45 are 0 gain (minimum angle of view) of the amplifier 39. It is a directivity pattern of the left
and right channels at the time of.
[0024]
As shown in FIG. 5, in the microphone of this embodiment, the directivity is continuously
changed from the directivity pattern similar to that of the conventional MS stereo microphone to
the unidirectional pattern in which the front direction is the maximum sensitivity. As the angle of
view is wide, stereo sound pickup with excellent left / right separation by MS method is
performed, and an acoustic zoom effect is realized to emphasize the sound emitted from the
target object in accordance with the zooming of the image. Can.
[0025]
FIG. 6 is a view showing the configuration of a fourth embodiment of the stereo microphone for
video camera of the present invention.
The difference from the third embodiment is that the low frequency component of the output of
the microphone unit 46 is removed by the high pass filter 50 and then input to the adder 52. The
other configuration is all shown in FIG. It is the same as the embodiment of. In the figure, 47, 48
and 49 are microphone units, 51 is a delay device, 53, 55 and 56 are adders, and 54 is an
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amplifier.
[0026]
The directivity at the final output of the microphone configured in this way has a pattern as
shown in FIG. 5 according to the gain of the amplifier 54 in the high frequency band bordering
on the cutoff frequency of the high pass filter 50 and in the low frequency band Regardless of
the gain of the amplifier 54, it becomes omnidirectional.
[0027]
Therefore, in the microphone of this embodiment, the reduction of the sound collection SN ratio
due to wind noise and low frequency vibration noise is similar to that of the nondirectional
microphone, and the sound collection SN ratio higher than that of the conventional MS
microphone is maintained. As in the third embodiment, the acoustic zoom effect can be realized
in the frequency band where it is possible to easily sense a change in directivity upon hearing.
[0028]
As apparent from the above description of the embodiment, in the stereo microphone for video
camera according to the present invention, the apparent two microphone positions obtained by
combining the outputs of the M microphone and the S microphone are four. It becomes the
center of the square which two microphone units form, and it can construct the stereo
microphone by the level difference completely.
Furthermore, there is no deterioration of directivity due to the influence of reflection and
diffraction of the case, and while being incorporated in the case, good characteristics as the MS
method can be maintained.
[0029]
In addition, by providing an omnidirectional region in the low frequency region, the drop in
sound pickup SN ratio due to wind noise or low frequency vibration noise is made comparable to
that of a nondirectional microphone, which is higher than that of a conventional MS microphone.
The sound pickup SN ratio can be maintained.
[0030]
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In addition, by changing the gain of the S microphone according to the zoom control signal of the
optical system, from the directivity pattern similar to that of the conventional MS-type stereo
microphone, to the pattern of unidirectivity in which the front direction has the maximum
sensitivity, Since the directivity can be changed continuously, when the angle of view is wide, an
acoustic zoom effect is performed, which performs excellent stereo sound separation with left
and right separation and emphasizes the sound emitted by the subject aimed at the zooming of
the image. Can be realized.
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