JP2009141789A - Stereo sound pickup device and sound recorder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stereo sound pickup device that can pick up sound other than from the front without having a sound lack or background noise. <P>SOLUTION: The stereo sound pickup device has: a single directional center microphone 11 disposed toward the center front; an omnidirectional left microphone 12 disposed at the left side of the center microphone; an omnidirectional right microphone 13 disposed at the right side of the center microphone; a first subtract means 22 that subtracts the right microphone output from the left microphone output; a second subtraction means 23 that subtracts the left microphone output from the right microphone output; a third subtraction means 24 that subtracts the first subtract means output from the center microphone output to output a right channel signal; and a fourth subtraction means 25 that subtracts the second subtract means output from the center microphone output to output a left channel signal. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a stereo sound collection device that collects sound in stereo and a recording device including the stereo sound collection device.

  2. Description of the Related Art Conventionally, a sound collection device that performs stereo sound collection with a sense of presence by using a stereo microphone is known. As a sound pickup method in such a conventional stereo sound pickup device, a single-directional microphone is used as a left channel side microphone and a right channel side microphone for performing stereo sound pickup. MS method using a non-directional microphone instead of a directional microphone, a unidirectional microphone arranged toward the front of the center, and a microphone having a bi-directionality in the left-right direction superimposed on it It has been known.

  FIG. 3 is a circuit diagram showing an example of a conventional stereo sound pickup apparatus. This apparatus includes a left microphone 31 on the left channel side, a right microphone 32 on the right channel side, a buffer amplifier 33 that outputs a stereo left channel signal Lout based on an audio signal from the left microphone 31, and audio from the right microphone 32. A buffer amplifier 34 is provided that outputs a stereo right channel signal Rout based on the signal. The audio signal from the left microphone 31 is output as a stereo left channel signal Lout through a buffer amplifier 33, and the audio signal from the right microphone 32 is output as a stereo right channel signal Rout through a buffer amplifier 34.

  Note that the sound collection device that performs stereo sound collection and the like includes a plurality of microphones capable of changing the orientation of the main axis, and accepts selection of one sound collection mode from a plurality of types of sound collection modes. It is also known that the direction of the main axis of the microphone is changed to an angle corresponding to the sound collection mode and the sound signal processing corresponding to the sound collection mode is performed (see, for example, Patent Document 1).

JP 2007-214913 A

  However, according to the stereo sound collecting device using the above-described unidirectional microphone, there may be a case where the sound collected from the front center direction becomes weak. For this reason, it is necessary to determine the angles and distances of the left microphone and the right microphone so that no void occurs. In addition, according to the stereo sound pickup apparatus using omnidirectional microphones for the left and right microphones such as the above-described MS system, background noise other than the sound pickup direction is superimposed regardless of the installation positions of the left microphone and the right microphone. There's a problem. In particular, low-frequency background noise in an unvoiced section is annoying. For this reason, it is necessary to reduce noise by a filter having the characteristics of low-frequency cut and high-frequency cut.

  An object of the present invention is to provide a stereo sound collecting device that does not cause a void in view of the problems of the prior art. Another object is to provide a stereo sound pickup device that can reduce background noise. Still another object is to provide a stereo sound pickup device that can pick up sounds from other than the front.

  In order to achieve this object, a stereo sound pickup apparatus according to a first aspect of the present invention includes a unidirectional central microphone arranged toward the center front, and an omnidirectional left microphone arranged on the left side of the central microphone. A microphone, an omnidirectional right microphone arranged on the right side of the central microphone, first subtracting means for subtracting the output of the right microphone from the output of the left microphone, and the left microphone from the output of the right microphone Second subtracting means for subtracting the output of the central microphone, third subtracting means for subtracting the output of the first subtracting means from the output of the central microphone to output a right channel signal, and the output of the central microphone And a fourth subtracting means for subtracting the output of the 2 subtracting means and outputting a left channel signal. Here, as the subtraction means, for example, one using an operational amplifier is applicable.

  In this configuration, the first subtracting unit subtracts the audio signal (R) from the right microphone from the audio signal (L) from the left microphone. The second subtracting unit subtracts the audio signal (L) from the left microphone from the audio signal (R) from the right microphone. The third subtracting unit subtracts the output (LR) of the first subtracting unit from the audio signal (L + R) from the central microphone, and outputs a stereo right channel signal (Rout). The fourth subtracting unit subtracts the output (R−L) of the second subtracting unit from the audio signal (L + R) from the central microphone, and outputs a stereo left channel signal (Lout).

  At this time, in the outputs (LR, RL) of the first subtracting means and the second subtracting means, the background noise of the same level from the left microphone and the right microphone is canceled out at the same level. This includes components such as no reflected sound and sound from the side or back. Therefore, the left channel signal (Lout) and the right channel signal (Rout) obtained by subtracting these outputs (LR, RL) from the audio signal (L + R) from the central microphone are While including components such as reflected sound, it is clear without background noise. In addition, no void occurs due to the audio signal from the central microphone.

  A stereo sound collecting apparatus according to a second invention is characterized in that, in the first invention, the first to fourth subtracting means are constituted by operational amplifiers, and the output of the central microphone is an output via the operational amplifier. To do.

  A stereo sound pickup apparatus according to a third invention is characterized in that, in the first invention, the frequency characteristics of the central microphone are flattened by correcting the frequency characteristics in the low frequency range.

  A stereo sound pickup apparatus according to a fourth invention is characterized in that, in the first invention, a gain adjustment is performed on any one of the output of the right microphone and the output of the left microphone, or the output of the central microphone. .

  A recording device according to a fifth invention comprises the stereo sound pickup device according to any one of the first to fourth inventions, and a recording means for performing stereo recording based on a stereo signal obtained by the stereo sound pickup device. It is characterized by doing.

  According to the present invention, since the left and right stereo signals are obtained by subtracting the differences between the left and right omnidirectional microphones from the output of the unidirectional central microphone, the hollow state is reliably ensured. It is possible to obtain a clear stereo signal in which background noise is canceled while avoiding it. In addition, in a place where there is reflection by a wall, it is possible to collect sound that produces a surround effect in which reverberant sound from the rear direction is added to stereo sound from the front direction. At that time, by changing the gain of the central microphone, it is possible to change the surround effect or to enhance the stereo sound field.

  FIG. 1 is a diagram showing a configuration of a microphone in a stereo sound pickup apparatus included in a recording apparatus according to an embodiment of the present invention. As shown in the figure, this sound collecting device includes a unidirectional central microphone 11 disposed toward the front center, an omnidirectional left microphone 12 disposed on the left side of the central microphone 11, and a central microphone 11. Is provided with an omnidirectional right microphone 13 arranged on the right side. The left microphone 12 and the right microphone 13 are used mainly for collecting sound with respect to the components of the left channel and the right channel of the stereo signal, respectively. The recording device includes recording means for performing stereo recording based on a stereo signal obtained by the stereo sound pickup device.

  FIG. 2 is a circuit diagram showing a circuit configuration in the stereo sound pickup apparatus. As shown in the figure, in this circuit, the non-inverting input terminal is connected to the central microphone 11, the operational amplifier IC21 whose output side is fed back to the inverting input terminal, the left microphone 12 is connected to the non-inverting input terminal, and the right microphone 13 is connected. The operational amplifier IC22 connected to the inverting input terminal and the right microphone 13 are connected to the non-inverting input terminal, the operational amplifier IC23 connected to the inverting input terminal and the non-inverting input terminal are connected to the output terminal of the operational amplifier IC21, An operational amplifier IC24 whose inverting input terminal is connected to the output terminal of the operational amplifier IC22, and an operational amplifier IC25 whose noninverting input terminal is connected to the output terminal of the operational amplifier IC21 and whose inverting input terminal is connected to the output terminal of the operational amplifier IC23. Is provided. The operational amplifier IC21 constitutes a voltage follower.

  In this configuration, based on the audio signal L from the left microphone 12 and the audio signal R from the right microphone, the operational amplifier IC22 outputs a difference signal LR obtained by subtracting the audio signal R from the audio signal L. The operational amplifier 23 outputs a differential signal RL obtained by subtracting the audio signal L from the audio signal R. The audio signal L + R from the central microphone 11 is input to the non-inverting input terminals of the operational amplifiers ICs 24 and 25 through the operational amplifier IC21.

  The operational amplifier IC24 subtracts the differential signal LR from the operational amplifier IC22 from the signal L + R output from the operational amplifier IC21, and outputs a right channel signal Rout. The operational amplifier IC25 subtracts the differential signal RL from the operational amplifier IC23 from the signal L + R output from the operational amplifier IC21, and outputs a left channel signal Lout. The left channel signal Lout and the right channel signal Rout constitute a stereo signal and are used for stereo recording by a recording device.

  At this time, since the operational amplifier ICs 22 and 23 take the difference between the audio signals L and R from the non-directional left microphone 12 and right microphone 13, background noise from all directions at the same level at the same time, etc. The components of are countered. Since the remaining components are subtracted from the signal L + R from the central microphone 11, the sound components 14 and 15 from the left and right diagonal directions shown in FIG. 1 are emphasized in the obtained stereo signal. Become.

  In addition, the relative signal level of the sound from the front center direction varies depending on the gain and directivity of each microphone 11-13. When the gains of the microphones 11 to 13 are in the range of 3 [dB] to -6 [dB] and are at substantially the same level, the best effect is exhibited. By adjusting the gain of the central microphone 11, the gain of each microphone can be made substantially the same. However, since the frequency characteristic of the unidirectional microphone is lowered in the low frequency range, the frequency characteristic of the omnidirectional microphone is almost flat. Therefore, the frequency characteristic of the central microphone 11 is low in the low frequency range of the microphone. It is preferable to correct the level by raising the level.

  Further, in order to adjust the overall gain of each of the microphones 11 to 13, a non-inverting amplifier circuit may be formed for the operational amplifier to which the signal output of each microphone is input. As an example, the operational amplifier IC21 to which the signal output of the central microphone 11 in FIG. 2 is input constitutes a voltage follower. The output of the operational amplifier IC21 is divided by a resistor and connected to the inverting input terminal of the operational amplifier IC21. As a result, a non-inverting amplifier circuit is configured, the gain is adjusted by amplifying the output of the central microphone 11, and the output is input to the operational amplifier IC24 and the operational amplifier IC25 which are subtraction means.

  Further, since the difference is taken between the audio signals L and R from the left and right omnidirectional microphones 12 and 13, sound that is not at the same level at the same time, such as reflected sound or sound from the side. These signal components are added to the stereo signal including the signal components for the sound from the rear. Therefore, if the gain of the central microphone 11 is too small, a sound field with a sound image having no localization is generated. There is also some sound collection effect in the left-right direction. In addition, when the levels of the microphones and the microphone gain are set to appropriate values, the obtained stereo signal has a stereo effect with a sense of surround due to a sense of stereo in the forward direction or a reflected sound from the rear.

  As described above, according to the present embodiment, it is possible to avoid the hollow state by the central microphone 11. Further, since the difference between the audio signals L and R from the left microphone 12 and the right microphone 13 is taken, it is possible to cancel the background noise and obtain a clear stereo signal for hearing. Therefore, it is possible to eliminate the low-frequency background noise in the silent section, which is a concern when recording is performed using only the conventional stereo microphone.

  In addition, according to the conventional MS recording, a unidirectional microphone is arranged toward the front center direction, and a bidirectional microphone is placed on top of this so that the sound from the front direction can be obtained. However, according to the present embodiment, it is possible to collect the stereo sound in the forward direction in a place where there is no reflection by the wall, and in a place where there is a reflection from the wall, It is possible to collect a sound that exhibits a surround effect in which a reverberant sound from the rear is added to a stereo sound from the front. In that case, the surround effect can be changed or the stereo sound field can be emphasized by changing the gain of the central microphone 11.

  At this time, even if the sound source is near or far away, it is possible to perform stereo sound collection with some emphasis on the stereo effect. In addition, the circuit configuration of the stereo sound pickup device can be made symmetrical with respect to the left channel and the right channel.

  In the above description, an example in which the operational amplifier IC21 is used as a non-inverting amplifier circuit for adjusting the gain of the output of the central microphone 11 has been described. However, depending on the gains of the left microphone 12 and the right microphone 13, non-inverted similarly in the outputs of the left and right microphones. An amplifier circuit may be installed to match the gain with the central microphone 11.

It is a figure which shows the structure of the microphone in the stereo sound collection device which concerns on one Embodiment of this invention. It is a circuit diagram which shows the circuit structure in the stereo sound-collecting apparatus of FIG. It is a circuit diagram which shows an example of the conventional stereo sound-collecting apparatus.

Explanation of symbols

  11: Central microphone, 12: Left microphone, 13: Right microphone, 14, 15: Sound component from oblique direction, 21-25: Operational amplifier IC, 31: Left microphone, 32: Right microphone, 33, 34: Buffer amplifier .

Claims (5)

A unidirectional central microphone placed towards the center front,
An omnidirectional left microphone arranged on the left side of the central microphone;
An omnidirectional right microphone arranged on the right side of the central microphone;
First subtracting means for subtracting the output of the right microphone from the output of the left microphone;
Second subtracting means for subtracting the output of the left microphone from the output of the right microphone;
Third subtracting means for subtracting the output of the first subtracting means from the output of the central microphone to output a right channel signal;
And a fourth subtracting unit for subtracting the output of the second subtracting unit from the output of the central microphone to output a left channel signal. The first to fourth subtracting means are composed of operational amplifiers,
The stereo sound pickup apparatus according to claim 1, wherein the output of the central microphone is an output via an operational amplifier.   The stereo sound pickup device according to claim 1, wherein the frequency characteristics of the central microphone are flattened by correcting the frequency characteristics in the low frequency range.   The stereo sound pickup device according to claim 1, wherein the output of any one of the output of the right microphone and the output of the left microphone or the output of the center microphone is adjusted. The stereo sound collecting device according to any one of claims 1 to 4,
A recording device comprising recording means for performing stereo recording based on a stereo signal obtained by the stereo sound pickup device.

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