JP3186909B2 - Stereo microphone for video camera - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[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 One-point stereo sound collecting microphones include a pair microphone system and a coaxial system. In the pair microphone system, two microphones having the same characteristics are arranged at an appropriate interval and an opening angle formed by the main axes of the two microphones is an appropriate size.
The level difference and phase difference between the two microphone outputs can be used as the direction information of the sound source. On the other hand, in the coaxial system, two directional microphones having the same characteristics are arranged at the same position, and the orientation is determined so that the opening angle between the main axes of the two microphones is about 90 to 120 °. Only the level difference between the outputs of the two microphones is used as the direction information of the sound source.

[0003] In the case of the pair microphone system, if the installation of the two microphones is optimal, it is possible to perform excellent stereo sound pickup which is difficult to obtain with the coaxial system, but the distance between the two microphones and the direction of the main axis are sound pickup. Fine adjustment is required according to the target sound source and the acoustic characteristics of the recording site, and a coaxial microphone is often used in terms of ease and reproducibility. In the coaxial system, two systems, an MS system and an XY system, are used.

FIG. 7 shows an example of the configuration of a conventional MS stereo microphone. As shown, unidirectional M
A (mid) microphone 1 and a bidirectional S (side) microphone 2 are arranged close to each other so that their directional axes are orthogonal to each other, and a sum signal and a difference signal of the outputs of the M microphone 1 and the S microphone 2 are formed. A microphone to be generated. 3 and 4 in the figure are adders. FIG. 8 shows a directivity pattern in which the main axis direction of the M microphone 1 of the MS system microphone configured as shown in FIG. 7 is set to 0 degree. One scale indicated by the concentric circle is 10 dB. In FIG.
5 is the directivity of the M microphone 1, 6 is the S microphone 2
The polarity of the output of the S microphone 2 is +, for sound waves arriving from the hemisphere on the main axis (−90 degrees) side,
On the opposite (90 degree) side, it becomes-. Therefore, assuming that the polarity of the M microphone 1 is +, the directivity of the signal obtained by adding the outputs of the M microphone 1 and the S microphone 2 is 7, and the directivity of the signal obtained by subtracting the output of the S microphone 2 from the output of the M microphone 1 is obtained. It looks like 8. Therefore, it is possible to obtain a stereo two-channel signal on the left side of the output of the adder 3 and on the right side of the output of the adder 4 in FIG.

[0005] In the XY system, two unidirectional microphones having directivity as shown in 5 of FIG. 8 are arranged such that the angle between their main axes is 90 to 120 °, and the two microphones are placed close to each other. It is a method of arranging. Since the coaxial stereo microphone is a microphone that uses only the level difference between the outputs of the two microphones as information on the direction of the sound source, it is necessary to arrange the two microphones at one point in space. However, in the XY system, since two unidirectional microphones are used, they can be arranged close to each other. However, it is impossible to arrange the two microphones completely at one point, and purely. It is not possible to extract only the level difference. On the other hand, in the case of the MS system, the M microphone and the S microphone are arranged close to each other in the vertical direction, and a sum signal and a difference signal of the two microphones are generated. Since two microphones are arranged at one point in the horizontal plane, a stereo microphone having only a level difference can be completely configured.

Therefore, the stereo microphone of the MS system is excellent in localization of the reproduced sound image because only the level difference is used as the direction information. In addition, by adjusting the sensitivity of the S microphone, the directivity pattern and the left and right sides are adjusted. Since the opening angle in the direction of the maximum sensitivity of the channel can be changed, it is easy to make adjustments in consideration of the reverberation characteristics at the recording site, the size and spread of the reproduced sound image, etc.
The advantage as a coaxial stereo microphone is greater than that of the stereo microphone.

[0007]

However, in the stereo microphone of the MS system having the above configuration, if there is an obstacle that disturbs the sound field around each microphone unit, the sound wave is reflected by the obstacle. 8, 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 in the MS system as shown in FIG. Therefore, in order to mount a conventional MS-type microphone on a video camera, the microphone is spatially separated sufficiently from the housing so that the microphone is not affected by reflection or diffraction of sound waves by the housing of the video camera. There is a need. Also,
As described above, since the M microphone and the S microphone need to be arranged in the vertical direction, the space required for the microphone in the vertical direction increases. For the above reasons, there has been a problem that the video camera cannot be reduced in size in the case where the conventional MS-type microphone is built in the housing.

In general, the MS type microphone is a primary sound pressure gradient type microphone. However, the sound pressure gradient type microphone basically has low sound pressure sensitivity in the main axis direction in a low frequency range. It is more susceptible to wind noise and vibration noise than non-directional microphones having flat frequency characteristics. Therefore, if the conventional MS-type microphone is incorporated in a small-sized video camera, the sound-collecting SN ratio in a low frequency range is reduced due to vibration generated by a mechanical system inside the housing, and when used outdoors, due to wind. There was a point.

In the MS system, the opening angle of the left and right channels in the direction of the maximum sensitivity can be changed by adjusting the sensitivity of the S microphone, but in the case of the conventional MS system, such sensitivity adjustment is a fine adjustment. In this case, there is a problem that an acoustic zoom effect such as emphasizing a sound emitted from a subject in the front direction cannot be realized in synchronization with a change in the angle of view of the optical system of the video camera.

The microphone for a video camera according to the present invention comprises:
In order to solve the above problems, it is possible to maintain good characteristics as a stereo microphone even when the microphone is built in a video camera housing.
It is an object of the present invention to provide a stereo microphone for an MS system video camera having a small reduction in the ratio and having an acoustic zoom function adapted to zooming of an image.

[0011]

In order to achieve the above object, a stereo microphone for a video camera according to the present invention is provided.
Using four omnidirectional microphone units, these are arranged so as to be located at the vertices of a square, and an M microphone is placed at both ends of the other diagonal by using a pair of units at both ends of one diagonal of the square. An S microphone is formed by electrical signal processing using a certain pair of units.

Further, in the low frequency range of the frequency range to be picked up, an area in which the directivity of the final output is omnidirectional is provided. 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.

[0013]

The stereo microphone for a video camera of the present invention having the above-described structure receives sound using four omnidirectional microphone units arranged in a plane, and performs electrical signal processing on the output of each microphone unit. Therefore, four microphone units can be arranged on the top or bottom surface of the video camera housing. On the surface constituting the outer shape of the object placed in the free sound field, only on a plane parallel to the traveling direction of the sound wave, since the sound pressure distribution is not affected by the reflection and diffraction of the object, the microphone of the present invention is used. By attaching to the top or bottom surface of the housing, the directivity inherent in the MS system shown in FIG. 8 can be maintained at least for a sound source located in a horizontal plane including the video camera. Also, since the four omnidirectional microphone units are located at the vertices 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. .

Further, by making the low frequency region non-directional, it is possible to prevent the sound pressure sensitivity from lowering in the low frequency region, so that the noise due to wind noise concentrated at low frequencies and low frequency vibration noise can be reduced. The decrease in the sound SN ratio can be reduced.

Further, by making the gain of the output of the S microphone variable in the range of 0 or more and 2 or less, continuous from the state of the stereo microphone by the MS system to the state of maximum sensitivity in the microphone front (video camera front) direction. It is possible to change the directivity, and to achieve an acoustic zooming effect.

[0016]

Embodiments of the present invention will be described below in detail. FIG. 1 is a diagram showing the configuration of a first embodiment of a stereo microphone for a video camera according to the present invention. In FIG. 1, reference numerals 9, 10, 11, and 12 denote omnidirectional microphone units, which are arranged so as to be located at respective vertexes of a square of an appropriate size. The output of the microphone unit 10 is input to the delay unit 13. Delay time τ of delay unit 13
Is my kilophone unit 9 and microphone unit 10
Is given by τ = d / c, where d is the distance between and c is the speed of sound. The output of the delay unit 13 is subtracted from the output of the microphone unit 9 by the adder 14. The directivity pattern at the output of the adder 14 is similar to the pattern 5 in FIG. 8, and the output of the adder 14 corresponds to the output of the unidirectional M microphone. The adder 15 outputs the output of the microphone unit 11 and the microphone microphone unit 12.
, And the directivity pattern at this output is the same as 6 in FIG. 8, and the output of the adder 15 corresponds to the output of the bidirectional S microphone. The output of the adder 15 is amplified by the amplifier 16. Adder 1
7 and the adder 18 are the output of the amplifier 16 and the adder 1 respectively.
4 to output a sum signal and a difference signal. In the final output of the stereo microphone having the configuration as shown in FIG. 1, if the gain of the amplifier 16 is 2, the directivity patterns shown in 7 and 8 in FIG. 8 can be obtained.

The center of the primary sound pressure gradient type microphone is 2
In the stereo microphone for a video camera according to the present embodiment, the M microphone and the S microphone formed by signal processing are four omnidirectional microphone units 9-1 to -1 each.
3 will be located at the center of the square. Therefore, the apparent two microphone positions obtained by combining the outputs of the M microphone and the S microphone are also at the center of the square, and a stereo microphone based on only the level difference can be completely configured. In addition, the reflection of the housing,
There is no deterioration in directivity due to the influence of diffraction, and it is possible to maintain good characteristics as a stereo microphone of the MS system while being built in the housing.

FIG. 2 is a diagram showing the configuration of a second embodiment of the video camera microphone 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. All other configurations are shown in FIG. This is the same as 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.

The directivity at the output of the adder 25 of the microphone configured as described above is omnidirectional in a low frequency range with the cutoff frequency of the high-pass filter 23 as a boundary.
In the high frequency region, the light is unidirectional.

FIG. 3 shows that the distance between the first microphone unit 19 and the second microphone unit 20, the distance between the third microphone unit 21 and the fourth microphone unit 22 is 10 mm, and the cut-off frequency of the high-pass filter 23 is 200 Hz. 9 shows the directivity pattern of the final output (left channel) of the microphone according to the present embodiment when. In the figure, reference numeral 30 denotes a case where the frequency is 100 Hz,
31 is a directivity pattern when the frequency is 2 kHz. In the final output, the directivity pattern of the MS system is obtained in the high frequency range almost in the same manner as in the first embodiment, but becomes omnidirectional in the low frequency range.

Therefore, in the microphone of the present embodiment, since the sound pressure sensitivity does not decrease in the low frequency range, the decrease in the picked-up SN ratio due to wind noise or low-frequency vibration noise is about the same as that of the omnidirectional microphone. Yes, it is possible to maintain a higher sound collection S / N ratio than that of a conventional MS-type microphone.

FIG. 4 is a diagram showing the configuration of a third embodiment of the stereo microphone for a video camera according to the present invention. First
The difference from the first embodiment is that the gain of the amplifier 39 for amplifying the output of the adder 38 is variable, and all other configurations are the same as those of the first embodiment shown in FIG.
In the figure, 32, 33, 34, and 35 are microphone units, 36 is a delay unit, and 37, 38, 40, and 41 are adders.

The gain of the amplifier 39 is determined according to the zoom control signal of the optical system. The gain is set so that the gain is 2 when the angle of view of the video is the widest, the gain decreases as the angle of view becomes narrower, and the gain becomes 0 when the angle of view is the narrowest. FIG. 5 shows the directivity pattern of the final output of the microphone of this embodiment. In the figure, reference numerals 42 and 43 denote left channel and right channel directivity patterns when the gain of the amplifier 39 is 2 (the angle of view is maximum), respectively.
Reference numerals 4 and 45 denote directivity patterns of the left and right channels when the gain of the amplifier 39 is 0 (the angle of view is minimum).

As shown in FIG. 5, in the microphone of this embodiment, the directivity is continuously changed from a directivity pattern similar to that of the conventional MS stereo microphone to a unidirectional pattern in which the front direction has the maximum sensitivity. When the angle of view is wide, the MS method provides excellent stereo sound pickup with left and right separation, and an acoustic zoom effect that emphasizes the sound emitted by the target subject in accordance with the zooming of the image. Can be realized.

FIG. 6 is a diagram showing the configuration of a fourth embodiment of the stereo microphone for a video camera according to the present invention. Third
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 before being input to the adder 52. All other configurations are the same as those of the third embodiment shown in FIG. Same as the example. 47 in the figure,
48 and 49 are microphone units, 51 is a delay unit, 5
3, 55 and 56 are adders and 54 is an amplifier.

The directivity of the final output of the microphone thus configured has a pattern as shown in FIG. 5 in accordance with the gain of the amplifier 54 in a high frequency range with the cutoff frequency of the high-pass filter 50 as a boundary. In the frequency range, the antenna becomes omnidirectional regardless of the gain of the amplifier 54.

Therefore, in the microphone according to the present embodiment, the reduction of the picked-up SN ratio due to wind noise or low-frequency vibration noise is almost the same as that of the omnidirectional microphone, and the conventional M
A higher sound-collecting SN ratio than the S-type microphone can be maintained, and an acoustic zoom effect can be realized in a frequency band in which a change in directivity is easily perceived in the same manner as in the third embodiment. .

[0028]

As is apparent from the above description of the embodiment, in the stereo microphone for a video camera of the present invention, the apparent two microphone positions obtained by combining the outputs of the M microphone and the S microphone are four. The center of the square formed by the two microphone units makes it possible to form a stereo microphone that is based solely on the level difference. Furthermore, there is no deterioration in directivity due to the influence of reflection and diffraction of the housing, and good characteristics can be maintained as the MS system while being built in the housing.

Further, by providing an omnidirectional region in the low frequency region, the reduction of the picked-up S / N ratio due to wind noise or low frequency vibration noise can be made comparable to that of the omnidirectional microphone.
It is possible to maintain a higher sound collection S / N ratio than a conventional MS-type microphone.

Further, by changing the gain of the S microphone according to the zoom control signal of the optical system, the conventional M
Since the directivity can be changed continuously from the directivity pattern similar to the S-type stereo microphone to the unidirectional pattern where the front direction has the maximum sensitivity, the left and right separation is excellent when the angle of view is wide. In addition to performing stereo sound pickup, it is possible to realize an acoustic zoom effect that emphasizes the sound emitted by the target subject in accordance with the zooming of the video.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a stereo microphone for a video camera according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a stereo microphone for a video camera according to a second embodiment of the present invention.

FIG. 3 is a directional pattern diagram of a stereo microphone for a video camera according to a second embodiment of the present invention.

FIG. 4 is a configuration diagram of a stereo microphone for a video camera according to a third embodiment of the present invention.

FIG. 5 is a directional pattern diagram of a stereo microphone for a video camera according to a third embodiment of the present invention.

FIG. 6 is a configuration diagram of a stereo microphone for a video camera according to a fourth embodiment of the present invention.

FIG. 7 is a configuration diagram of a conventional MS system stereo microphone.

FIG. 8 is a directional pattern diagram of a conventional MS stereo microphone.

[Explanation of symbols]

9, 10, 11, 12 Non-directional microphone unit 13 Delay unit 14, 15, 17, 18 Adder 16 Amplifier

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-168085 (JP, A) JP-A-4-167698 (JP, A) JP-A-63-144699 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H04R 1 / 40,3 / 00,5 / 027 H04N 5/225

Claims (4)

(57) [Claims] 1. A line connecting both first and second microphone units that are both non-directional and are omni-directional and that are both omni-directional and arranged at appropriate intervals. Third and fourth microphone units disposed at both ends of another diagonal of a square having one diagonal, and a delay unit for giving an appropriate delay to the output of the second microphone unit; A first adder for adding the output of the delay unit to the output of the first microphone unit in a reverse phase, and the output of the fourth microphone unit to the output of the third microphone unit in a reverse phase. A second adder for adding, an amplifier for amplifying the output of the second adder, a third adder for adding the output of the amplifier in-phase to the output of the first adder, Output of the first adder A stereo microphone for a video camera, further comprising a fourth adder for adding an output of the amplifier in a reverse phase. 2. The stereo microphone for a video camera according to claim 1, further comprising a high-pass filter for removing a low-frequency component of an output of the first microphone unit input to the first adder. 3. The stereo microphone for a video camera according to claim 1, wherein the gain of the amplifier to which the output of the second adder is input is variable within a range of 0 or more and 2 or less. 4. The stereo microphone for a video camera according to claim 2, wherein the gain of the amplifier which receives the output of the second adder as input is variable in a range of 0 or more and 2 or less.