JP6981559B2 - Sound collecting device - Google Patents

Description

The present invention relates to a technique of arranging a plurality of microphones three-dimensionally to collect sound in a target direction (hereinafter, also referred to as a target sound).

A technique is known in which a plurality of microphones are arranged at a plurality of different positions near the focal position of a reflecting portion having a rotating paraboloid, and beamforming processing is performed so as to emphasize only the target direction sound based on the collected signal. (See Patent Document 1). In addition, the beam forming filter is designed from the transfer function (array manifold vector) from the target sound source position or target sound source direction to each microphone and the spatial correlation matrix of the noise signal received by the microphone (spatial correlation matrix of noise). Is known to emphasize the target sound source and suppress noise (see Non-Patent Document 1). Further, in Patent Document 1, a transmission function from a target sound source to a microphone is measured in advance for a device in which a plurality of microphones are installed near the focal position of a reflecting portion, and a beamforming filter is designed using this. By doing so, it is shown that the target sound source can be emphasized more efficiently than when there is no reflecting portion. In addition, by installing multiple microphones near the focal position, only in the front direction of the reflecting part (the direction of the rotation axis of the rotating paraboloid of the reflecting part and the opening direction (the direction on the focal side)). It is possible to form a directivity even in a direction deviated from the front direction, and it is possible to emphasize the sound in an arbitrary direction.

Japanese Unexamined Patent Publication No. 2015-198411

Tadashi Asada, "Sound Array Signal Processing-Sound Source Localization, Tracking and Separation-", Corona Publishing Co., Ltd., 2011.

As shown in Patent Document 1, there is a system that emphasizes a target sound by beamforming sound collection using a device in which a plurality of microphones are installed near the focal position of a reflecting portion.
However, when the reflecting portion is small, there is a problem that directional sound collection cannot be performed in the low frequency range. The effect is particularly remarkable when the wavelength of the sound wave is longer than the diameter of the reflecting portion. An example of the directivity characteristic of the reflecting portion is shown in Reference 1.
(Reference 1) "Sound collection microphone", [online], [Search on February 20, 2017], Internet <URL: http://www.kobayasi-riken.or.jp/news/No118/118_3. htm>

An object of the present invention is to provide a sound collecting device capable of realizing directional sound collection in a low frequency range even when the reflecting portion is small.

In order to solve the above problems, according to the first aspect of the present invention, the sound collecting device has a wavelength larger than the diameter of the rotating paraboloid even when the rotating paraboloid constituting the sound collecting device is small. This is to emphasize long signals with high accuracy. The sound collecting device includes a reflecting part having a rotating paraboloid, P as one of two or more integers, P microphones, and M and N as one of one or more integers, respectively, and P ≧. M + N, M microphones are placed near the focal position of the rotating paraboloid, N microphones are placed near the center of the focal side surface of the rotating paraboloid, and the edges of the rotating paraboloid. The diameter of the circle formed by the portions is equal to or less than the maximum wavelength width of the signal of interest.

According to the present invention, it is possible to realize the same level of directional sound collection in the low frequency range by using a reflection unit smaller than the conventional one, or by using a reflection unit having the same size as the conventional one. It has the effect of being able to achieve directional sound collection in the bass range.

The front view which shows the arrangement example of a microphone. The side view which shows the arrangement example of a microphone. The perspective view which shows the arrangement example of a microphone. The figure for demonstrating the effect of a reflector. The figure for demonstrating the microphone arrangement for efficiently emphasizing the target sound source. The figure for demonstrating the arrangement example of a parabolic reflector and a microphone. The figure which shows the sensitivity characteristic of the sound pickup apparatus of the prior art. The figure which shows the sensitivity characteristic of the sound collecting apparatus which concerns on 1st Embodiment. The functional block diagram of the sound collecting apparatus which concerns on 1st Embodiment. The figure which shows the example of the processing flow of the sound collecting apparatus which concerns on 1st Embodiment. The figure which shows the arrangement example 1 of the microphone. The figure which shows the arrangement example of the microphone with respect to the parabolic reflector. The figure which shows the arrangement example 2 of a microphone. The figure which shows the arrangement example of the microphone with respect to the parabolic reflector. The figure which shows the example of the appearance of the arrangement of the microphone with respect to the parabolic reflector of the 2nd Embodiment. The figure which shows the example of the appearance of the arrangement of the microphone with respect to the parabolic reflector of the third embodiment.

Hereinafter, embodiments of the present invention will be described. In the drawings used in the following description, the same reference numerals are given to the components having the same function and the steps performing the same processing, and duplicate description is omitted. In the following description, the processing performed for each element of the vector or matrix shall be applied to all the elements of the vector or matrix unless otherwise specified.

<Points of the first embodiment>
In the present embodiment, by arranging the microphones three-dimensionally, a difference in arrival time of sound between the microphones occurs. This time difference (phase difference) is used to improve the directivity. With such a configuration, sound can be collected up to a frequency in which a half wavelength is included in the distance between the microphone 20-n in the back and the microphone 20-m in the front.

As shown in Patent Document 1, there is a method of arranging a plurality of microphones in a plane near the focal position of a parabolic reflector to emphasize the sound in the target direction. However, there is no proposal for a method of collecting sound in a target direction by arranging it not only in the vicinity of the focal position but also in the bottom portion of the parabola away from the focal point as proposed in the present embodiment.

In the present embodiment, the microphone 20-n is arranged at the center position of the surface of the parabolic reflector 10 on the focal side in addition to the vicinity of the focal position of the reflecting portion (hereinafter, also referred to as a parabolic reflector) 10 having a rotating paraboloid. .. 1 and 2 and 3 are a front view, a side view, and a perspective view showing an arrangement example of the microphone, respectively. With such a configuration, it is possible to accurately estimate the phase difference in the low frequency range that cannot be detected by the microphone 20-m arranged near the focal position of the parabolic reflector 10, and to realize the directional sound collection in the low frequency range of the target direction sound. ..

In this embodiment, M microphones 2 are located near the focal position of the parabolic reflector 10.
Place 0-m. Further, N microphones 20-n are arranged near the center position of the surface of the parabolic reflector 10 on the focal side. Hereinafter, the microphone 20-m is focused on the microphone 2
The 0-m microphone 20-n is also referred to as a bottom microphone 20-n. m = 1 _m , 2 _m ,…, M _m , n = 1 _n , 2 _n ,…, N _n . The subscripts m and n are indexes indicating that they are a focal point microphone and a bottom microphone, respectively. With such a configuration, directional sound collection including the bass range is possible.

In the conventional parabolic reflector, the effect of the reflector is remarkably reduced at a frequency having a wavelength longer than the diameter thereof. The effect of the reflector is that when the microphone is installed near the focal position of the reflector, a sharp directivity is formed at an angle close to the front direction of the reflector.

At frequencies whose wavelength is shorter than the diameter of the reflector, the sound is concentrated at one point depending on the direction of arrival of the sound, and the sound pressure increases by that point. That is, the effect of the reflector is high. FIG. 4 shows the situation. The sound coming from the front direction of the reflector is reflected by the reflector, gathers at the focal point (point A) of the reflector, and the sound pressure at the focal point of the reflector becomes high. Further, the sound arriving from a direction slightly deviated from the front of the reflector is reflected by the reflector and gathers at the point B slightly deviated from the focal point of the reflector, and the sound pressure at the point B becomes high. Since the point at which the sound pressure increases differs depending on the direction of arrival of the sound, a large amplitude difference occurs in the sound observed by a plurality of microphones installed near the focal position depending on the direction of arrival of the sound. By performing beamforming processing mainly using this amplitude difference information, it is possible to realize sound collection that emphasizes sound in any direction.

However, at frequencies where the wavelength is longer than the diameter of the reflector, the effect of the reflector is significantly reduced. Therefore, in a plurality of microphones installed near the focal position of the reflector, the amplitude difference depending on the direction of arrival of sound becomes smaller (compared to the case where the wavelength is shorter than the diameter of the reflector). Furthermore, since the microphones are concentrated near the focal position, the phase difference depending on the direction of arrival of sound is small. Therefore, even if the beamforming process is performed, a sharp directivity cannot be formed.

In the present embodiment, the arrangement of the microphone is devised so that a sharp directivity can be formed without using the reflection of the reflector for a frequency having a wavelength longer than the diameter of the reflector. Also, from the viewpoint of cost, it is better to have as few microphones as possible, so it is desirable to add as few microphones (bottom microphones) as possible.

First, a microphone arrangement for efficiently emphasizing the target sound source will be described. As shown in FIG. 5, when the target sound source is on a straight line passing through the positions of the two microphones, the target sound source can be efficiently emphasized. The directivity formed by beamforming using two microphones has a symmetrical shape with respect to the line passing through the microphones, so if the axial direction is the direction to be emphasized, only one direction can be emphasized. On the other hand, if the direction other than the axial direction is to be emphasized, there is a direction having the same sensitivity in the direction other than the direction to be emphasized (the direction in which the angle with the axis is the same (the direction in which the angle is line symmetric with respect to the axis)). In this way, if the microphone is arranged so that the target sound source is on a straight line passing through the microphone, the target sound can be efficiently emphasized. Further, as described in Non-Patent Document 1, it is desirable that the microphone spacing is narrower than the half wavelength of the target frequency without causing spatial folding distortion, and the spacing is as small as possible so that the phase difference can be easily observed. Wider is better. That is, an interval of about half a wavelength of the target frequency is desirable.

In this embodiment, as shown in FIG. 6, one or more microphones 20-m (three in the example of FIG. 6) are installed near the focal position of the parabolic reflector 10 and the center of the surface of the parabolic reflector on the focal side. By installing one microphone 20-n at the position, for frequencies having a wavelength longer than the diameter of the parabolic reflector 10, the microphone 20-n installed at the center of the surface of the parabolic reflector 10 and the focal position Beamforming processing is performed by mainly utilizing the arrival time difference (phase difference) of the sound between the nearby microphone 20-m and the target sound is efficiently emphasized. For example, when the front direction (solid line in FIG. 6) of the parabolic reflector 10 is the target sound direction, two microphones 20-n installed at point D and microphones 20-1 _m installed at point A are used. Mainly used for beamforming. When the direction deviated from the front (broken line in FIG. 6) is the target sound direction, mainly two _{microphones, the microphone 20-n installed at the point D and the microphone 20-3 m installed at the point C, are used.} Beamforming. In this way, by installing one microphone 20-n at the center position of the surface of the parabolic reflector 10 in addition to the vicinity of the focal position of the parabolic reflector 10, the frequency has a longer wavelength than the diameter of the parabolic reflector 10. On the other hand, beamforming mainly using the phase difference can efficiently form directivity in the target sound direction.

Further, since the microphone interval is preferably half the wavelength of the target frequency, the distance from the focal point (point A) of the parabolic reflector 10 to the center of the parabolic surface is about 0.25 to 1 times the diameter of the parabolic reflector 10. Yes, especially it is desirable to be about half. It is advisable to design the shape of the parabolic reflector 10 in this way.

An example of actually forming directivity is shown. FIG. 7 shows the sensitivity characteristics in each direction when the microphone 20-m is installed only near the focal position of the parabolic reflector 10 having a diameter of 30 cm and beamforming is performed so as to emphasize the 0 degree direction. FIG. 8 shows when microphones 20-m and 20-n are installed near the focal position of the parabolic reflector 10 having a diameter of 30 cm and at the center of the surface of the parabolic reflector 10 and beamforming is performed so as to emphasize the 0 degree direction. Sensitivity characteristics for each direction. Looking at the results at 1 kHz, which has a wavelength longer than 30 cm in diameter, the sensitivity difference between the 0 degree direction and the 80 degree direction when the microphone 20-m is installed only near the focal position is 10 dB, whereas the parabolic reflector It can be seen that when the microphone 20-n is also installed at the center position of the 10 surface, the sensitivity difference is as large as 15 dB. By installing the microphone 20-n at the center of the surface of the parabolic reflector 10 in this way, it is possible to form sharper directivity for frequencies with wavelengths longer than the diameter of the parabolic reflector 10. Become.

<Sound collecting device 100 according to the first embodiment>
9 and 10 show a functional block diagram and a processing flow of the sound collecting device 100 according to the first embodiment.
The sound pickup device 100 includes P microphones 20-p and a parabolic reflector 10, and further includes a CPU, RAM, and a computer having a ROM in which a program for performing the following processing is recorded. .. This computer is functionally configured as shown below. The sound collecting device 100 includes an AD conversion unit 120, a frequency domain conversion unit 130, a filtering unit 160, a time domain conversion unit 170, a filter calculation unit 150, and a transmission characteristic storage unit 140.

<Parabolic reflector 10>
The parabolic reflector 10 has a rotating paraboloid. The rotating paraboloid has a shape, material, and size that can reflect sound waves and forms a focal point. In this embodiment, the parabolic reflector 10 is a rigid body having a rotating paraboloid. The circular diameter formed by the edge of the rotating paraboloid is about 0.25 to 1 times or more the maximum wavelength width in the wavelength width to be handled, and it is particularly desirable that the diameter is about half a wavelength (0.5 times) or more. For example, when the wavelength width handled by the wavelength of a sound wave is 0.01 to 1 m, it is desirable that the diameter of the circle formed by the edge of the rotating paraboloid is about 0.5 m or more. The material of the parabolic reflector 10 is preferably a material that easily reflects sound waves (in other words, a material having a high reflectance coefficient), and a hard material is preferable. Therefore, in the present embodiment, a rigid body having a parabolic shape, which is hard and has an area, is used as the parabolic reflector 10.

<Microphone 20-p>
Sound is picked up using P microphones 20-p (s1), and the analog signal (sound pick-up signal) is A.
Output to D conversion unit 120. Of the P microphones 20-p, M microphones 20-m are arranged near the focal position of the parabolic reflector 10, and N microphones 20-n are on the surface of the parabolic reflector 10 on the focal side. It is placed near the center position. However, P is any of integers of 2 or more, M and N are each of integers of 1 or more, P = M + N, p = 1,2, ..., P, and m. = 1 _m , 2 _m ,…, M _m , n ＝ 1 _n , 2 _n ,…, N _n . The microphone 20-m and the microphone 20-m'are arranged at different positions near the focal position formed by the parabolic reflector 10. Here, m'is one of 1, 2, ..., M, and m ≠ m'. Further, for example, the microphone 20-n and the microphone 20-n'are arranged at different positions near the center position of the surface on the focal side of the parabolic reflector 10. Here, n'is one of 1, 2, ..., N, and n ≠ n'.

<Position of microphone 20-p with respect to parabolic reflector 10>
P microphones 20-p may be arranged so that the determinant det (R) of the noise spatial correlation matrix R is maximized. However, the noise spatial correlation matrix R (ω) is ^{calculated using only the noise transmission characteristic b →} _k (ω) as shown in the following equation (see Non-Patent Document 1).

Place P microphones 20-p to increase the signal-to-noise ratio. At this time, M microphones 20-m are arranged near the focal position. In addition, M microphones 20-m are arranged at different positions so that the correlation between channels is low. For example, as described in Patent Document 1, M microphones 20-m may be arranged so that the correlation between sound waves converted into electric signals by M microphones 20-m is low. .. Further, N microphones 20-n are arranged near the center position of the surface on the focal side of the parabolic reflector 10.

(Arrangement example 1)
The conditions for arranging the microphones are shown in FIG. The direction of the central axis of the parabolic reflector 10 is described as the coordinate axis y. Let y = H1 be a plane that passes through the intersection of the central axis of the parabolic reflector 10 and the rotating paraboloid of the parabolic reflector 10 and is orthogonal to the central axis of the parabolic reflector 10. Further, let y = H2 be a plane that passes through the focal position of the parabolic reflector 10 and is orthogonal to the central axis of the parabolic reflector 10. However, in FIG. 11, when the direction of the parabolic reflector 10 when viewed from the focal point is the positive direction on the y-axis, H1> H2.

In this arrangement example, the microphone 20-p is arranged so as to satisfy the following.

The microphone 20-m is arbitrarily arranged on the y = H2 plane and in a region having a radius r2 from the focal position (diagonal region in FIG. 11, circular region when viewed from the front). However, the radius r2 is equal to or less than the radius r1 of the parabolic reflector 10. For example, the shaded area in FIG. 11 corresponds to the above-mentioned "near the focal position". The expression "near the focal position" includes the focal position itself, and the microphone 2
0-m may be placed at the focal position.

When y = H2 + D (where H1> H2 + D) is the plane separated by the distance D from the y = H2 plane toward the y = H1 plane, the microphone 20-n is inside the parabolic reflector 10 and y = H1. N microphones 20-n are arbitrarily arranged in the region sandwiched between the plane and the y = H2 + D plane (the satin area in FIG. 11). For example, the satin area in FIG. 11 corresponds to the "near the center position of the surface on the focal side" of the parabolic reflector 10. However, the plane that passes through the edge of the parabola-type reflector 10 and is orthogonal to the central axis of the parabola-type reflector 10 (when multiple planes that pass through the edge of the parabola can be defined, the plane closest to the y = H1 plane) is y =. When the H3 plane is set, the distance D is set so that the plane y = H2 + D is located between the plane y = H1 and the plane y = H3 (H3 ≤ H2 + D <H1). By setting the distance D in this way, the N microphones 20-n are arranged between the plane y = H2 + D and the focal side surface of the parabolic reflector 10. Further, the distance D is 0.25 to 1 times the diameter of the parabolic reflector 10, and is particularly preferably about 0.5 times.

FIG. 12 shows an example of arrangement of the microphone 20-p with respect to the parabolic reflector 10.

In this embodiment, the microphone 20-m is supported by a support portion 191 having a shape that does not easily block the waves arriving at the parabolic reflector 10.

In FIG. 12, the support portion 191 is a structure including a plane y = H2 located near the focal position formed by the parabolic reflector 10, and is for holding M microphones 20-m on the plane. Multiple vacancies are formed. For example, M'(M'> M) pores are formed, and each microphone 20-m is embedded in any of the M'pores. In this embodiment, the support portion 191 includes a mesh member 191A and a support member 191B. The support member 191B is a rod-shaped structure of a regular quadrangular pyramid having the bottom of the parabolic-shaped reflector 10 as the apex and forming each side extending from the apex. A net-like net-like member 191A is provided in the same plane as the bottom surface of a regular quadrangular pyramid. The support member 191B connects the parabolic reflector 10 and the mesh member 191A, and fixes the network member 191A to the parabolic reflector 10. The network member 191A is a structure including a surface located near the focal position formed by the parabolic reflector 10. Further, the net-like member 191A is formed with a plurality of holes for holding the microphone 20-m. In other words, M microphones 20-m can be embedded in any of the meshes of the mesh member 191A.

The microphone 20-n is arranged near the center position (bottom) of the focal point side surface of the parabolic reflector 10, in this example, on the fixing member of the support member 191B.

(Arrangement example 2)
The conditions for arranging other microphones are shown in FIG. In this arrangement example, the microphone 20-p is arranged so as to satisfy the following.
The microphone 20-m is placed at an arbitrary position within a region (hatched portion in FIG. 13, spherical shape) within a radius r2 from the focal position. For example, the shaded area in FIG. 13 corresponds to the vicinity of the focal position.

The microphone 20-n is located inside the parabolic reflector 10 and in the region sandwiched between the planes of y = H1 and y = H3 (the three-dimensional space formed by the parabolic reflector 10), and is separated from the focal position by a distance of D or more. Arbitrarily arranged in the area (the satin-finished portion in FIG. 13). However, r2 has a size of about 1/4 of the radius r1 of the parabolic reflector 10. The distance D is about half the diameter of the parabola.

In FIG. 14, the support portion 191 is a rod-shaped structure that connects the parabolic reflector 10 and the microphone 20-m.

The shape of the support portion 191 is not limited to the above-mentioned shape, and may be any shape as long as it does not easily block the waves arriving at the parabolic reflector 10 and can support the microphone 20-m. .. The microphone 20-m is supported by the support portion 191 and is arranged near the focal position.

<AD converter 120>
The AD conversion unit 120 converts P analog signals picked up by P microphones 20-p into digital signals x ^→ (t) = [x ₁ (t),…, x _P (t)] ^T. (S2), frequency domain converter 130
Output to. t represents a discrete-time index.

<Frequency domain converter 130>
^{The frequency domain conversion unit 130 first inputs the digital signal x →} (t) = [x ₁ (t),…, x _P (t)] ^T output by the AD conversion unit 120, and sets a Q sample for each channel. It stores in a buffer and generates a ^{digital signal x →} (τ) ＝ [x ^→ ₁ (τ),…, x ^→ _P (τ)] ^{T in frame units.} τ is the index of the frame number. x ^→ _p (τ) = [x _p ((τ-1) Q + 1),…, x _p (τQ)] (1 ≦ p ≦ P). Q depends on the sampling frequency, but in the case of 48kHz sampling, around 2048 points is appropriate. Next, frequency domain transform section 130, the signal of the digital signal x ^→ (τ) the frequency domain for each frame ^{X → (ω, τ) =} [X 1 (ω, τ), ..., X P (ω, τ )] ^{Convert to T} (s3) and output. ω is the index of discrete frequencies. One of the methods for converting a time domain signal into a frequency domain signal is a high-speed discrete Fourier transform, but the present invention is not limited to this, and another method for converting into a frequency domain signal may be used. The frequency domain signal X ^→ (ω, τ) is output for each frequency ω and frame τ.

<Transmission characteristic storage unit 140>
The transmission characteristic storage unit 140 stores the transmission characteristic A ^→ (ω) = [a ^→ (ω), b ^→ ₁ (ω),…, b ^→ _K (ω)] measured in advance using the sound collecting device 100. Remember. a ^→ (ω) ＝ [a ₁ (ω),…, a _P (ω)] ^T is the transmission characteristic at the frequency ω between the target sound and P microphones, in other words, a ^→ (ω) ) = [A ₁ (ω),…, a _P (ω)] ^T is the transmission characteristic of the target sound to each microphone included in the microphone array at the frequency ω. k = 1,2,…, K, where K is the number of noises, b _k ^→ (ω) ＝ [b _k1 (ω),…, b _kP (ω)] ^T , noise k and P Transmission characteristics at frequency ω to and from the microphone, in other words, b _k ^→ (ω) ＝ [b _k1 (ω),…, b _kP (ω)] ^T to each microphone included in the microphone array. It is the transmission characteristic of the noise k at the frequency ω. The transmission characteristic A ^→ (ω) may be prepared in advance by a theoretical formula or a simulation, not by prior measurement.

<Filter calculation unit 150>
^{The filter calculation unit 150 takes out the transmission characteristic A →} (ω) from the transmission characteristic storage unit 140, calculates ^{the filter W →} (ω), and outputs it to the filtering unit 160. ^{For example, the filter W →} (ω) used for signal processing that suppresses the acoustic signal from a specific position or direction is calculated.

^{For example, the filter W →} (ω) can be designed by the same method as in the prior art. For example, <1> filter design method based on the SN ratio maximization criterion described in Reference 2, <2> filter design method based on Power Inversion, and <3> one or more blind spots (noise gain). Filter design method by the minimum dispersion distortion-free response method with the constraint condition), <4> Filter design method by the Delay-and-Sum Beam Forming method, <5> Filter by the most probable method. ^{The filter W →} (ω) can be designed by the design method, <6> AMNOR (Adaptive Microphone-array for noise reduction) method, or the like.
[Reference 2] International Publication No. WO2012 / 086834 Pamphlet

For example, when the delay sum method is used as the base, the filter W ^→ _DS1 (ω) is calculated by the following equation.

For example, when the maximum likelihood method is used as the base, the filter W ^→ _DS2 (ω) is calculated by the following equation.

For example, in the case of the filter design method based on the minimum dispersion distortion-free response method with one or more blind spots as constraints, the filter W ^→ _DS3 (ω) is calculated by the following equation.

However, f _S (ω) and f _k (ω) are frequencies ω related to the target sound and noise k (k = 1,2,…, K), respectively.
Represents the passage characteristics in. For example, the transmission characteristic a ^→ (ω) depends on the direction θ. The transmission characteristic a ^→ (ω, θ)
If it can be prepared in advance ^{, the filter W →} (ω, θ) is calculated ^{using the transmission characteristic a →} (ω, θ), and the filtering unit 160 can perform signal processing _{in a specific direction θ s.} also,
If the transmission characteristic a ^{→ (ω) can be prepared in advance as the transmission characteristic a →} (ω, θ, D) that depends on the direction θ and the distance D ^{, use the transmission characteristic a →} (ω, θ, D). , Filter W ^→ (ω, θ, D) is calculated, and in the filtering unit 160, a specific position (a position specified by a specific direction θ _s and a distance D _H ).
Signal processing can be performed.

With such a configuration, for frequencies whose wavelength is shorter than the diameter of the parabolic reflector 10, beamforming is mainly performed using M microphones 20-m.
For frequencies with wavelengths greater than or equal to the diameter of the parabolic reflector 10, a beamforming filter is used to perform beamforming using M microphones 20-m and other microphones 20-n. Is designed, and the above-mentioned beamforming is executed in the following filtering unit 160.

<Filtering unit 160>
The filtering unit 160 receives the filter W ^→ (ω) from the filter calculation unit 150 in advance, receives the frequency region signal X ^→ (ω, τ), and for each frame τ, the frequency region signal X for each frequency ω ∈ Ω. ^→ (ω, τ) = [X ₁ (ω, τ),…, _XP (ω, τ)] ^{Apply the filter W → (ω) to T as shown} in the following equation (s4), and output signal Output Y (ω, τ).

For example, the filtering unit 160 makes the sound picking characteristics of the acoustic signals emitted from at least a plurality of positions or directions in space different based on the sound picking signal by the microphone 20-p and the sound picking signal by the microphone 20-p'. Anything is fine. "Different sound collection characteristics" means, for example, that the acoustic signal emitted at a specific position is locally picked up so that the acoustic signal emitted at another position is not picked up as much as possible, or conversely, a specific sound is picked up. It means that the acoustic signal emitted at a position is suppressed (silenced) and only the acoustic signal emitted at another position is collected.

<Time domain conversion unit 170>
The time domain conversion unit 170 converts the output signal Y (ω, τ) of each frequency ω ∈ Ω in the τ frame into a time domain (s5), and converts the frame unit time domain signal y (τ) in the τ frame into a time domain. Further, the obtained frame unit time domain signal y (τ) is concatenated in the order of the index of the frame number, and the time domain signal y (t) is output. The method of converting the frequency domain signal into the time domain signal is an inverse transform corresponding to the conversion method used in the processing of s3, for example, a high-speed discrete inverse Fourier transform.

<Effect>
With such a configuration, the idea of reducing the inter-channel correlation in Patent Document 1 can be inherited, the impulse response length can be shortened, and the SN ratio at the time of receiving a sound can be increased. Therefore, it becomes possible to analyze waves arriving from various directions (furthermore, information indicated by the waves) stably and at the same time with high spatial resolution. For example, it is possible to suppress unnecessary sound direction components as compared with the conventional case, and to collect sound that emphasizes the target direction sound including low frequencies. In particular, the directivity in the frequency range where the wavelength of the sound wave is longer than the diameter of the parabolic reflector can be made sharper than before. In this embodiment, the filter W ^→ (ω) is calculated in advance, but the filter calculation unit 150 determines the frequency after the sound source position and the microphone arrangement are determined according to the calculation processing capacity of the sound collecting device 100 and the like. It may be configured to calculate the filter W ^{→ (ω) for each.}

<Modification example>
Although the directivity of the microphone is not mentioned in the present embodiment, the correlation between the transmission characteristics may be reduced and uncorrelated may be achieved by using a mixture of microphones having various directivity. For example, the directivity of the microphone is not limited, but microphones having various directivities such as omnidirectional, unidirectional, bidirectional, and hypercardioid are mixed and used. If electroacoustic transducers having different directivity are arranged at the same position, the transmission characteristics with the same control point will be different. For example, when an omnidirectional microphone and a unidirectional microphone are placed at the same position, the transmission characteristics between the control point and the omnidirectional microphone and the control point and the unidirectional microphone The transmission characteristics between them will be different. Therefore, under this condition, the change in the transmission characteristics due to the difference in directivity is utilized, and the correlation between the transmission characteristics is further reduced to achieve uncorrelatedness. In other words, the directivity of at least one of the plurality of microphones is different from the directivity of the other microphone to achieve uncorrelatedness.

In the present embodiment, of the P microphones 20-p included in the sound collecting device 100, the M microphones 20-m are arranged near the focal position of the parabolic reflector 10, and the N microphones 20-n are parabolic. It is arranged near the center position of the surface of the mold reflector 10 on the focal side. That is, P = M + N. However, the microphone holon may be placed in a portion other than the vicinity of the focal position or the center position of the surface on the focal side. That is, P> M + N may be set.

In the present embodiment, in the filtering unit 160, for each frequency ω ∈ Ω, the frequency region signal X ^→ (ω, τ) = [X ₁ (ω, τ),…, X _P (ω, τ)] ^T , Filter W ^→ (ω) is applied to output the output signal Y (ω, τ), but for frequencies whose wavelength is shorter than the diameter of the parabolic reflector 10, M microphones 20-m It may be configured to perform beam forming using only. For example, let Th be the index of the frequency corresponding to the diameter of the parabolic reflector 10, and in ω <Th, the frequency region signal X ^→ (ω, τ) = [X ₁ (ω, τ), ... , X _P (ω, τ)] ^{T is obtained, but when ω ≧ Th, the frequency region signal X →} _m (ω, τ) corresponding to the M analog signals picked up by the M microphones 20-m. = [X _{1_m} (ω, τ),…, X _{M_m} (ω, τ)] ^T
Only the filter W ^→ _m (ω) is applied, and the output signal Y _m (ω, τ) = [Y _{1_m} (ω, τ),…, Y _{M_m} (ω, τ)] ^T is output. The filter calculation unit 150 calculates ^{only the filter W →} _m (ω) when ω ≧ Th.
When ω ≧ Th, the transmission characteristic storage unit 140 needs to store only the transmission characteristics necessary for calculating the ^{filter W →} _{m (ω).} For example, when ω ≧ Th, the transmission characteristic at the frequency ω between the target sound and M microphones a ^→ (ω) ＝ [a _{1_m} (ω),…, a _{M_m} (ω)] ^T and noise k _{Memorize the transmission characteristics b k} ^→ (ω) ＝ [b _{k_m} (ω),…, b kM_m (ω)] ^T between M microphones at the frequency ω. With such a configuration, the same effect as that of the first embodiment can be obtained.

In the present embodiment, the filtering process is performed in the frequency domain, but the filtering process may be performed in the time domain. For example, P digital signals in the time domain x ₁ (t),…, x _P (t)
In addition, the time domain filter coefficient may be convoluted in the time domain for each channel p, and the convolution results of all channels may be added. In this case, it is not necessary to provide the frequency domain conversion unit 130 and the time domain conversion 170. Further, the transmission characteristic storage unit 140 stores the transmission characteristics in the time domain measured in advance using the sound collecting device 100, and the filter calculation unit 150 calculates the filter in the time domain.

<Second embodiment>
The part different from the first embodiment will be mainly described.

The sound collecting device according to the present embodiment also includes P microphones 20-p and a parabolic reflector 10. However, of the P microphones 20-p, the M microphones 20-m are arranged near the focal position of the parabolic reflector 10, and the L microphones 20-l are the central axes of the parabolic reflector 10. It is placed at a distance in the front direction.
However, P is any of integers of 2 or more, M and L are each of integers of 1 or more, P = M + L, p = 1,2, ..., P, and m. = 1 _m , 2 _m ,…, M _m , l = 1 _l , 2 _l ,…, L _l , subscript l (L) indicates that the microphone is located at a distance in the front direction. It is an index. With such a configuration, directional sound collection including the bass range becomes possible as in the first embodiment. An example of the appearance of the arrangement is shown in FIG. It is also possible to obtain the same effect as that of the first embodiment by placing the microphone 20-l on the front side of the focal position.

However, in the case of the present embodiment, since there is no restriction on the distance between the focal position and the microphone placed in front of the focal position, there is an advantage that the microphone can be placed at an arbitrary distance. For example, arrange L microphones 20-l so that the distance is 0.25 to 1 times the wavelength of the frequency for which the effect is desired. In particular, it is advisable to arrange L microphones 20-l so that the distance is 0.5 times. That is, it is preferable to install the microphone 20-l at a position about half the diameter of the parabolic reflector 10 whose frequency and wavelength match the frequency at which the effect of the reflector is low.

<Modification example>
In the present embodiment, the L microphones 20-l are arranged at positions separated from each other in the front direction of the central axis of the parabolic reflector 10, but they do not necessarily have to be arranged "on the central axis". The L microphones 20-l are arranged on the front side of the focal position of the parabolic reflector 10, and the distance from the focal position of the parabolic reflector 10 is 0.25 to 1 times the diameter of the parabolic reflector 10. Reflector 10 "near a point on the central axis"
It should be placed in. In particular, it is preferable to place it "near a point on the central axis" where the distance from the focal position is 0.5 times the diameter. In addition, M to the extent that the phase difference in the low frequency range can be estimated accurately.
It suffices if the microphones 20-m and the microphones 20-l are separated from each other, and the "nearby" in the above-mentioned "near point on the central axis" is the range in which such an effect can be obtained. Means. Assuming that the point on the central axis is O, for example, "near the point on the central axis" is in the sphere centered on the point O with a radius equal to or less than half the wavelength of the central frequency of the frequency band of the target sound. It is an area. In that case, the "near a point on the central axis" is the region within the sphere centered on the point O, which has a radius of half a wavelength of the center frequency of the frequency band at the maximum, and the minimum point O (radius is zero). When). The expression "near a point on the central axis" includes the point itself on the central axis, and the microphone 20-l.
May be placed at a point on the central axis.

<Third embodiment>
The part different from the first embodiment will be mainly described.

The sound collecting device according to the present embodiment also includes P microphones 20-p and a parabolic reflector 10. However, of the P microphones 20-p, of the P microphones 20-p, the M microphones 20-m are arranged near the focal position of the parabolic reflector 10, and the N microphones 20-. n is arranged near the center position of the surface of the parabolic reflector 10 on the focal side, and the L microphones 20-l are arranged at positions apart from each other in the front direction of the central axis of the parabolic reflector 10. However, P is any of integers of 3 or more, and M, N, and L are each of integers of 1 or more, and P = M + N + L. The arrangement of each microphone is as described in the first embodiment, the second embodiment, and modified examples thereof.

With such a configuration, directional sound collection including the bass range is possible. An example of the appearance of the arrangement is shown in FIG. By placing the microphone on both the bottom portion of the parabolic reflector 10 and the front side of the focal position, it is possible to obtain a higher effect than the first embodiment and the second embodiment. As in the first and second embodiments, the distance between the focal position and the microphone at the bottom of the parabola, and the distance between the focal position and the microphone installed in front of the focal point are the diameter of the parabolic reflector 10. It is about 0.25 to 1 times, and particularly preferably about half.

<Other variants>
The present invention is not limited to the above embodiments and modifications. For example, the various processes described above may not only be executed in chronological order according to the description, but may also be executed in parallel or individually as required by the processing capacity of the device that executes the processes. In addition, changes can be made as appropriate without departing from the spirit of the present invention.

<Programs and recording media>
Further, various processing functions in each device described in the above-described embodiments and modifications may be realized by a computer. In that case, the processing content of the function that each device should have is described by the program. Then, by executing this program on a computer, various processing functions in each of the above devices are realized on the computer.

The program describing the processing content can be recorded on a computer-readable recording medium. The recording medium that can be read by a computer may be, for example, a magnetic recording device, an optical disk, a photomagnetic recording medium, a semiconductor memory, or the like.

Further, the distribution of this program is performed, for example, by selling, transferring, renting, or the like a portable recording medium such as a DVD or a CD-ROM in which the program is recorded. Further, the program may be distributed by storing the program in the storage device of the server computer and transferring the program from the server computer to another computer via the network.

A computer that executes such a program first temporarily stores, for example, a program recorded on a portable recording medium or a program transferred from a server computer in its own storage unit. Then, when the process is executed, the computer reads the program stored in its own storage unit and executes the process according to the read program. Further, as another embodiment of this program, a computer may read the program directly from a portable recording medium and execute processing according to the program. Further, every time the program is transferred from the server computer to this computer, the processing according to the received program may be executed sequentially. Further, the above-mentioned processing is executed by a so-called ASP (Application Service Provider) type service that realizes the processing function only by the execution instruction and the result acquisition without transferring the program from the server computer to this computer. May be. It should be noted that the program includes information used for processing by a computer and equivalent to the program (data that is not a direct command to the computer but has a property that regulates the processing of the computer, etc.).

Further, although each device is configured by executing a predetermined program on a computer, at least a part of these processing contents may be realized by hardware.

Claims (2)

Even if the rotating paraboloid constituting the sound collecting device is small, it is a sound collecting device for accurately emphasizing a signal having a wavelength longer than the diameter of the rotating paraboloid.
A reflective part with a rotating paraboloid,
P is one of two or more integers, including P microphones
M and N are each one of integers of 1 or more, P ≧ M + N, M microphones are arranged near the focal position of the rotating paraboloid, and N microphones are located on the rotating paraboloid. Located near the center of the surface on the focal side,
The diameter of the circle formed by the end of the rotating paraboloid is less than or equal to the maximum wavelength width of the signal of interest.
Sound collecting device. The sound collecting device according to claim 1.
The diameter ranges from 0.25 to 1 times the maximum wavelength width of the signal of interest.
Sound collecting device.

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