JP2012165189A - Zoom microphone device - Google Patents

Abstract

A zoom microphone apparatus capable of realizing a narrow-directional speech enhancement technique having sharper directivity than before is provided.
A surface of a fixed reflector is provided with one support structure, 2N fixed reflectors (N is an integer of 1 or more), and 2N microphone arrays in which a plurality of microphones are linearly arranged. One microphone array is attached to the surface of the fixed reflector so that the microphone array direction of the microphone array and the microphone array of the microphone array are parallel to each other, and the surfaces of the two fixed reflectors to which the microphone array is attached form 90 degrees. The two fixed reflectors face each other so that the microphone array direction of the microphone array attached to the fixed reflector is 90 degrees and the microphone array direction of the microphone array attached to the other fixed reflector is 90 degrees. A fixed set of fixed reflectors (N sets) is attached to the support structure.
[Selection] Figure 18

Description

  The present invention relates to a zoom microphone apparatus that realizes a technique for enhancing a narrow range of sound including a desired direction (narrow-directed sound enhancement technique).

  For example, considering a case where a subject is zoomed in with a moving image shooting apparatus (video camera or camcorder) equipped with a microphone, it is preferable for moving image shooting that the sound from only the vicinity of the subject is enhanced in conjunction with the zoom in shooting. Such a technology (narrow-directed speech enhancement technology) for enhancing a narrow range of speech including a desired direction (target direction) has been researched and developed conventionally. Note that the relationship between the direction around the microphone and the sensitivity of the microphone is called directivity. The sharper the directivity in a certain direction, the more the sound in a narrow range including the direction is emphasized. The voice can be suppressed. Here, a conventional technique relating to a narrow-directional speech enhancement technique <a narrow-directional speech enhancement technique by selectively collecting reflected sounds> will be exemplified. In this specification, “speech” is not limited to a voice uttered by a person, but refers to a general “sound” such as a musical sound or an environmental noise as well as a voice of a person or an animal.

<Narrow-directed speech enhancement technology by selectively collecting reflected sounds>
A typical example of this technique is a multi-beam forming method (see Non-Patent Document 1). The multi-beam forming method is a narrow-directional speech enhancement technology that collects individual sounds such as direct sound and reflected sound, and can pick up the sound in the target direction with a high signal-to-noise ratio. Well studied.

Hereinafter, processing contents of the multi-beam forming method in the frequency domain will be described. Prior to explanation, symbols are defined. Let the frequency index be ω and the frame number index be k. A frequency domain representation of an analog signal received by M microphones is expressed as X ^→ (ω, k) = [X ₁ (ω, k), ..., X _M (ω, k)] ^T , with direction θ _s The direction of arrival of direct sound from the desired sound source is θ _s1 , and the direction of arrival of reflected sound is θ _s2 ,..., Θ _sR . T represents transposition and R-1 is the total number of reflected sounds. _Let W ^→ (ω, θ _sr ) be a filter that enhances the voice in the direction θ _sr . Here, r is an integer satisfying 1 ≦ r ≦ R.

In the multi-beam forming method, it is assumed that the arrival direction and arrival time of the direct sound and the reflected sound are known. In other words, the number of objects such as walls, floors, and reflectors that can clearly predict sound reflection is equal to R-1. The reflected sound number R-1 is often set to a relatively small value of 3 or 4. This is based on the fact that a high correlation is recognized between the direct sound and the low-order reflected sound. Since the multi-beam forming method is a method in which each sound is individually emphasized and synchronously added, the output signal Y (ω, k, θ _s ) is given by Equation (1). H represents Hermitian transpose.

A delay synthesis method will be described as a design method of the filter W ^→ (ω, θ _sr ). Assuming that direct sound or reflected sound arrives as a plane wave, the filter W ^→ (ω, θ _sr ) is given by equation (2). h ^→ (ω, θ _sr ) = [h ₁ (ω, θ _sr ),..., h _M (ω, θ _sr )] ^T is a propagation vector of speech coming from the direction θ _sr .

When linear microphone array assuming that the plane wave (M number of microphones microphone array are arranged in a straight line) _{^{arrives, h → (ω, θ sr}} ) elements h _m (ω, θ _sr) that constitute the formula It is given by (3). m is an integer satisfying 1 ≦ m ≦ M. c represents the speed of sound, and u represents the distance between adjacent microphones. j is an imaginary unit. τ (θ _sr ) represents a time delay with respect to the direct sound of the reflected sound coming from the direction θ _sr .

Finally, by converting the output signal Y (ω, k, θ _s ) to the time domain, a signal in which the sound of the sound source in the target direction θ _s is enhanced is obtained.

  FIG. 1 shows a functional configuration of the narrow directivity speech enhancement technique based on the multi-beam forming method.

Step 1
The AD converter 110 converts an analog signal output from the M microphones 100-1,..., 100-M into a digital signal x ^→ (t) = [x ₁ (t),..., X _M (t)] ^T Convert to Here, t represents an index of discrete time.

Step 2
The frequency domain transform unit 120 transforms the digital signal of each channel into a frequency domain signal by a technique such as fast discrete Fourier transform. For example, for the m-th (1 ≦ m ≦ M) microphone, N-point signals x _m ((k−1) N + 1),..., X _m (kN) are stored in the buffer. N is about 512 in the case of 16 KHz sampling. The frequency domain signal X ^→ (ω, k) = [X ₁ (ω, k),..., X _M (ω, k)] by subjecting the M-channel analog signal stored in the buffer to fast discrete Fourier transform processing. ^{Get T.}

Step 3
Each emphasis filtering unit 130-r (1 ≦ r ≦ R) corresponds to the frequency domain signal X ^→ (ω, k) = [X ₁ (ω, k),..., X _M (ω, k)] ^T. direction theta _sr filter _{^{W → H (ω, θ sr}} ) was applied, and outputs a direction theta _sr of audio enhancement signal Z _r (ω, k). That is, each emphasizing filtering unit 130-r (1 ≦ r ≦ R) performs the processing represented by Expression (4).

Step 4
The adder 140 receives the signals Z ₁ (ω, k),..., Z _R (ω, k) and outputs an addition signal Y (ω, k). The addition process is expressed by equation (5).

Step 5
The time domain conversion unit 150 converts the addition signal Y (ω, k) into the time domain and outputs a time domain signal y (t) in which the voice in the direction θ _s is emphasized.

J.L.Flanagan, A.C.Surendran, E.E.Jan, "Spatially selective sound capture for speech and audio processing," Speech Communication, Volume 13, Issue 1-2, pp.207-222, October 1993.

  According to the narrow-directional speech enhancement technique described above, the voice in any direction is collected without collecting the voice in the target direction at a high SN ratio so as not to be buried in the voice in the direction other than the target direction, and without requiring the drive control means described above. Can be emphasized, but it is difficult to achieve narrow directivity. In particular, human voice contains many frequency components from about 100 Hz to about 2 kHz, but with the above-described conventional technology, a sharp directivity of about ± 5 ° to ± 10 ° with respect to the target direction in such a low frequency band. It is difficult to realize sex. Under such circumstances, sound is picked up with a sufficient signal-to-noise ratio and can follow the sound in any direction without the need for physical movement of the microphone. In the past, there was no device suitable for realizing the narrow-directional speech enhancement technology having the characteristics.

  Therefore, an object of the present invention is to provide a zoom microphone apparatus that can realize a narrow-directional speech enhancement technique having sharper directivity than before.

  The zoom microphone device of the present invention includes one support structure, 2N fixed reflectors (N is an integer of 1 or more), and 2N microphone arrays in which a plurality of microphones are linearly arranged. In the zoom microphone device of the present invention, the microphone array is attached one by one to the surface of the fixed reflector so that the surface of the fixed reflector and the microphone array direction of the microphone array are parallel to each other. The surfaces to which the array is attached form 90 degrees, and the microphone array direction of the microphone array attached to one fixed reflector and the microphone array direction of the microphone array attached to the other fixed reflector form 90 degrees. In this way, a set of fixed reflectors (N sets) in which two fixed reflectors are fixed to face each other is attached to the support structure.

  With the zoom microphone device of the present invention, it is possible to realize a narrow directional speech enhancement technique having sharper directivity than before.

The figure which shows the function structure of the narrow directional speech enhancement technique by a multi-beam forming method as an example of a prior art. (A) A diagram schematically showing that narrow directivity cannot be sufficiently realized when only direct sound is considered, and (b) schematically showing that narrow directivity can be sufficiently realized when direct sound and reflected sound are considered. FIG. The figure which shows the direction dependence of the coherence in the case of based on the case of a prior art, and the principle of this invention. The figure which shows the function structure of the narrow directivity audio | voice emphasis apparatus which concerns on embodiment. The figure which shows the process sequence of the narrow directivity audio | voice enhancement method which concerns on embodiment. The figure which shows the structure of a 1st Example. The figure which shows the experimental result of a 1st Example. The figure which shows the experimental result of a 1st Example. The figure which shows the directivity by filter W- ^> ((omega), (theta)) in a 1st Example. The figure which shows the structure of a 2nd Example. The figure which shows the experimental result of a 2nd Example. The figure which shows the experimental result of a 2nd Example. The figure which shows the implementation structural example of this invention. (A) Top view. (B) Front view. (C) Side view. (A) The side view which shows another implementation structural example of this invention. (B) The side view which shows another implementation structural example of this invention. The figure which shows the usage pattern in the implementation structural example shown in FIG.14 (b). The figure which shows the implementation structural example of this invention. (A) Top view. (B) Front view. (C) Side view. The side view which shows the implementation structural example of this invention. The front view which shows the structure of a 3rd Example. The side view which shows the structure of a 3rd Example. The front view which shows the structure of the 1st modification of a 3rd Example. The front view which shows the structure of the 2nd modification of a 3rd Example. The front view which shows the structure of the 3rd modification of a 3rd Example. The front view which shows the structure of the 4th modification of a 3rd Example. The front view which shows the structure of the 5th modification of a 3rd Example.

"principle"
The principle of the present invention will be described. The present invention is sharp, based on the essence of microphone array technology that can follow sound in any direction based on signal processing, and to collect sound with a high S / N ratio by actively using reflected sound. One of the features is the combination of signal processing technologies that enable directivity.

Prior to the explanation, the symbols are defined again. The index of the discrete frequency is ω (there is a relationship of ω = 2πf between the frequency f and the angular frequency ω, so the index ω of the discrete frequency may be identified with the angular frequency ω. The frequency index "is also simply referred to as" frequency "), and the frame number index is k. The frequency domain representation of the kth frame of the analog signal received by M microphones is expressed as X ^→ (ω, k) = [X ₁ (ω, k), ..., X _M (ω, k)] ^T , microphone array Let W ^→ (ω, θ _s ) be a filter that emphasizes the frequency domain representation of the speech in the target direction θ _s with the frequency ω as viewed from the center of the. M is an integer of 2 or more. T represents transposition. At this time, a frequency domain signal (hereinafter referred to as an output signal) Y (ω, k, θ _s ) in which the frequency domain representation of the voice in the target direction θ _s is emphasized by the frequency ω is given by Expression (6). H represents Hermitian transpose.

The “center of the microphone array” can be arbitrarily determined, but generally, the geometric center of the arrangement of the M microphones is the “center of the microphone array”. For example, in the case of a linear microphone array, the microphones at both ends The middle point of the microphone is the “center of the microphone array”. For example, in the case of a planar microphone array arranged in a square matrix of m × m (m ² = M), the positions where the diagonal lines of the microphones at the four corners intersect are “microphone array”. The center of

There are various design methods for the filter W ^→ (ω, θ _s ), but here, a case based on a minimum variance distortion response method (MVDR method) will be described. In the minimum variance-free response method, the filter W ^→ (ω, θ _s ) is a voice in a direction other than the target direction θ _s using the spatial correlation matrix Q (ω) under the constraint condition of Equation (8) , “Speech in a direction other than the target direction θ _s ” is also referred to as “noise”) so that the power is minimized at the frequency ω (see Expression (7)). a ^→ (ω, θ _s ) = [a ₁ (ω, θ _s ), ..., a _M (ω, θ _s )] ^T is the sound source when it is assumed that there is a sound source in the direction θ _s This is a transfer characteristic at a frequency ω between M microphones. In other words, a ^→ (ω, θ _s ) = [a ₁ (ω, θ _s ), ..., a _M (ω, θ _s )] ^T is the direction θ _s to each microphone included in the microphone array. It is a transfer characteristic at the frequency ω of sound.

It is known that the filter W ^→ (ω, θ _s ), which is the optimal solution of the equation (7), is given by the equation (9).
(Reference 1) by Simon Haykin, translated by Hiroshi Suzuki et al., "Adaptive Filter Theory", First Edition, Science and Technology Publishing Co., Ltd., 2001. pp.66-73,248-255

  As can be seen from the fact that the inverse matrix of the spatial correlation matrix Q (ω) is included in the equation (9), it can be seen that the structure of the spatial correlation matrix Q (ω) is important for realizing sharp directivity. It can also be seen from equation (7) that the noise power depends on the structure of the spatial correlation matrix Q (ω).

Let {1, 2,..., P-1} be a set to which the noise arrival direction index p belongs. It is assumed that the index s in the target direction θ _s does not belong to the set {1, 2,..., P-1}. Assuming that P−1 noises come from any direction, the spatial correlation matrix Q (ω) is given by equation (10a). From the viewpoint of creating a filter that functions sufficiently even in the presence of a lot of noise, P is preferably a somewhat large value, and is assumed to be an integer of about M. Here, from the viewpoint of easily explaining the principle of the invention, the target direction θ _s is described as if it were a specific direction (therefore, directions other than the target direction θ _s are set as “noise” directions). As will be apparent from the embodiments described later, in practice, the target direction θ _s is an arbitrary direction that can be a target of speech enhancement, and a plurality of directions are generally assumed as directions that can be the target direction θ _s. Is done. From this point of view, the distinction between the target direction θ _s and the noise direction is almost subjective, and there are P number of directions that can be assumed as voice arrival directions regardless of whether the target sound or noise is distinguished. It is more accurate to determine different directions in advance and understand that one of the P directions selected is the target direction and the other directions are noise directions. Therefore, if the union of the set {1, 2, ..., P-1} and the set {s} is Φ, the spatial correlation matrix Q (ω) is included in multiple directions that are assumed as the voice arrival directions. transfer characteristics a to each microphone of the speech in each direction theta _phi to _{^{→ (ω, θ φ) =}} [a 1 (ω, θ φ), ..., a M (ω, θ φ)] T (φ∈Φ) Is a spatial correlation matrix expressed by Equation (10b). Note that | Φ | = P. | Φ | represents the number of elements of the set Φ.

Here, the transfer characteristic a ^→ (ω, θ _s ) of the voice in the target direction θ _s and the transfer characteristic a ^→ (ω, θ _p ) = of the voice in the direction p∈ {1,2, ..., P-1} [a ₁ (ω, θ _p ), ..., a _M (ω, θ _p )] Assume that ^T are orthogonal to each other. That is, it is assumed that there are P orthogonal basis sets that satisfy the condition expressed by Expression (11). The symbol ⊥ represents orthogonality. If A ^→ ⊥B ^→ , the inner product value of vector A ^→ and vector B ^→ is zero. Here, P ≦ M is satisfied. In addition, when the condition represented by Expression (11) is relaxed and it can be assumed that there are P basis sets that can be regarded as approximately orthogonal basis sets, P is about M, or is somewhat larger than M It is preferably a value.

At this time, the spatial correlation matrix Q (ω) can be expanded as shown in Equation (12). Equation (12) is a matrix V (ω) = [a ^→ (ω, θ _s ), a ^→ (ω, θ ₁ ),..., A ^→ (ω , θ _P-1 )] ^T and unit matrix Λ (ω) means that the spatial correlation matrix Q (ω) can be decomposed. ρ is an eigenvalue and a real number of the transfer characteristic a ^→ (ω, θ _φ ) satisfying the expression (11) based on the spatial correlation matrix Q (ω).

At this time, the inverse matrix of the spatial correlation matrix Q (ω) is given by Equation (13).

It can be seen that the noise power is minimized by substituting equation (13) into equation (7). If the noise power is minimized, directivity in the target direction θ _s is realized. Therefore, the fact that orthogonality is established between transfer characteristics in different directions is an important condition for realizing directivity with respect to the target direction θ _s .

Hereinafter, the reason why it is difficult to realize a sharp directivity with respect to the target direction θ _s in the prior art will be considered.

In the prior art, the filter is designed on the assumption that the transfer characteristic is composed only of direct sound. In reality, there is a reflected sound that is reflected from the sound source from the same sound source and reaches the microphone, but the reflected sound is considered to be a factor that deteriorates directivity and ignores the presence of the reflected sound. It was. If the steering vector of only direct sound coming from the direction θ is h ^→ _d (ω, θ) = [h _d1 (ω, θ), ..., h _dM (ω, θ)] ^T , conventionally, the transfer characteristic a ^→ _conv (ω, θ) = [a ₁ (ω, θ),..., A _M (ω, θ)] ^T is set as a ^→ _conv (ω, θ) = h ^→ _d (ω, θ). The steering vector is a complex vector in which the phase response characteristics at the frequency ω of each microphone with respect to the reference point are arranged for sound waves in the direction θ as viewed from the center of the microphone array.

Assuming that speech arrives at the linear microphone array as a plane wave, the m-th element h _dm (ω, θ) constituting the direct sound steering vector h ^→ _d (ω, θ) is given by, for example, the following equation (14a). m is an integer satisfying 1 ≦ m ≦ M. c represents the speed of sound, and u represents the distance between adjacent microphones. j is an imaginary unit. The reference point is half the total length of the linear microphone array (the center of the linear microphone array). The direction θ is defined as an angle formed by the direct sound arrival direction and the arrangement direction of the microphones included in the linear microphone array as seen from the center of the linear microphone array (see FIG. 6). There are various ways of expressing the steering vector. For example, if the reference point is the position of the microphone at one end of the linear microphone array, the mth element constituting the direct sound steering vector h ^→ _d (ω, θ). h _dm (ω, θ) is given by, for example, equation (14b). In the following description, it is assumed that the m-th element h _dm (ω, θ) constituting the direct sound steering vector h ^→ _d (ω, θ) is given by equation (14a).

The inner product value γ _conv (ω, θ) of the transfer characteristic in the direction θ and the transfer characteristic in the target direction θ _s is expressed by Expression (15). Note that θ ≠ θ _s .

Hereinafter, γ _conv (ω, θ) is referred to as coherence. The direction θ in which the coherence γ _conv (ω, θ) is 0 is given by equation (16). q is an arbitrary integer other than 0. In addition, since 0 <θ <π / 2, the range of q is limited for each frequency band.

In Expression (16), the only parameters that can be changed are the parameters (M and u) related to the size of the microphone array. Therefore, when the direction difference (angle difference) | θ−θ _s | is small, the microphone array It is difficult to reduce the coherence γ _conv (ω, θ) without changing the parameters related to the size of. In this case, the power of the noise is not sufficiently reduced, and directivity having a wide beam width with respect to the target direction θ _{s is} obtained as schematically shown in FIG.

On the other hand, according to the present invention, based on such consideration, the filter design for having a sharp directivity with respect to the target direction θ _s is coherence even when the direction difference (angle difference) | θ−θ _s | is small. Unlike the prior art, based on the knowledge that it is important to be able to reduce the noise sufficiently, it is characterized by positively considering reflected sound.

In each microphone of the microphone array, two types of plane waves, that is, a direct sound from the sound source and a reflected sound in which the sound from the sound source is reflected by the reflector 300 are mixed. Let the number of reflected sounds be Ξ. Ξ is a predetermined integer of 1 or more. At this time, the transfer characteristic a ^→ (ω, θ) = [a ₁ (ω, θ),..., A _M (ω, θ)] ^T directly transmits the sound in the direction that can be the target of speech enhancement to the microphone array. The sum of the direct sound transmission characteristics and the transmission characteristics of one or more reflected sounds that are reflected by the reflector and reach the microphone array, specifically, the direct sound and the ξth (1 ≦ ξ ≦ Ξ) If the arrival time difference from the reflected sound is τ _ξ (θ), and α _ξ (1 ≦ ξ ≦ Ξ) is a coefficient for taking into account the attenuation of the sound due to reflection, the direct sound as shown in equation (17a) This can be expressed as the sum of the steering vector and the steering vector of several reflected sounds in which the sound attenuation due to reflection and the arrival time difference with respect to the direct sound are corrected. h ^→ _rξ (ω, θ) = [h _r1ξ (ω, θ),..., h _rMξ (ω, θ)] ^T represents the steering vector of the reflected sound corresponding to the direct sound in the direction θ. α _ξ (1 ≦ ξ ≦ Ξ) is usually α _ξ ≦ 1 (1 ≦ ξ ≦ Ξ). For each reflected sound, if the number of reflections from the sound source to the microphone is one, α _ξ (1 ≦ ξ ≦ Ξ) represents the reflectance of the sound of the object reflected by the ξth reflected sound. You can think that it is.

Since it is desired to provide one or more reflected sounds to a microphone array composed of M microphones, it is preferable that one or more reflectors exist. From this point of view, assuming that there is a sound source in the target direction, the positional relationship between the sound source, the microphone array, and one or more reflectors is such that the sound from the sound source is reflected by at least one reflector. Each reflector is preferably arranged to reach the array. Each reflector has a two-dimensional shape (for example, a flat plate) or a three-dimensional shape (for example, a parabolic shape). Moreover, it is preferable that the size of each reflector is equal to or larger than the microphone array (about 1 to 2 times). In order to effectively use the reflected sound, the reflectance α _ξ (1 ≦ ξ ≦ Ξ) of each reflector is at least greater than 0, and more specifically, the amplitude of the reflected sound that reaches the microphone array is a direct sound. For example, each reflector is a rigid solid. The reflecting object may be a movable object (for example, a reflector) or an immovable object (a floor, a wall, or a ceiling). If an immovable object is set as a reflector, the steering vector of the reflected sound needs to be changed along with the change of the microphone array installation position (functions Ψ (θ) and Ψ _ξ (θ) described later are changed). (Refer to the above), and the filter calculation must be redone (reset). Therefore, in order to be robust against environmental changes, it is preferable that each reflector is a subordinate of the microphone array (in this case, it is assumed that the estimated number of reflected sounds is due to each reflector. become). Here, the “subordinate of the microphone array” refers to “a tangible object that can follow changes in the position and orientation of the microphone array while maintaining the positional relationship (geometric relationship) with respect to the microphone array”. A simple example is a configuration in which each reflector is fixed to a microphone array.

Hereinafter, from the viewpoint of specifically explaining the advantages of the present invention, Ξ = 1, the number of reflections of the reflected sound is one, and there is one reflector at a position L meters away from the center of the microphone array. Assume. The reflector is a thick rigid body. In this case, since Ξ = 1, the subscript representing this is omitted, and the expression (17a) can be expressed as the expression (17b).

Reflection sound steering vector h ^→ _r (ω, θ) = [h _r1 (ω, θ),…, h _rM (ω, θ)] The m-th element of ^T Similarly (see formula (14a)), it is represented by formula (18a). The function Ψ (θ) outputs the arrival direction of the reflected sound. When the direct sound steering vector is expressed by equation (14b), the reflected sound steering vector h ^→ _r (ω, θ) = [h _r1 (ω, θ),..., H _rM (ω, θ) ] The m-th element of ^T is expressed by Expression (18b). In general, the _ξth (1 ≦ ξ ≦ Ξ) steering vector h ^→ _rξ (ω, θ) = [h _r1ξ (ω, θ),…, h _rMξ (ω, θ)] The mth element of ^T Is expressed by equation (18c) or equation (18d). The function Ψ _ξ (θ) outputs the arrival direction of the ξth (1 ≦ ξ ≦ Ξ) reflected sound.

  Since the position of the reflector can be set as appropriate, the arrival direction of the reflected sound can be treated as a variable parameter.

Assuming that the flat reflector is in the vicinity of the microphone array (distance L is not extremely large compared to the size of the microphone array), coherence γ (ω, θ) is expressed by equation (19). Note that θ ≠ θ _s .

From equation (19), it can be seen that the coherence γ (ω, θ) of equation (19) may be smaller than the conventional coherence γ _conv (ω, θ) of equation (15). There are parameters (Ψ (θ) and L) that can be changed depending on how the reflector is placed in the second to fourth items of equation (19), so the first item h ^→ _d ^H (ω, θ) h ^→ _d (ω, θ) may be removed.

For example, for a linear microphone array, if a flat reflector is placed so that the microphone array direction is normal to the reflector, Ψ (θ) = π-θ holds for the function Ψ (θ), and Since the equation (20) is established for the arrival time difference τ (θ) between the sound and the reflected sound, the conditions of the equations (21) and (22) are generated in the elements constituting the equation (19). The symbol * is an operator representing a complex conjugate.

_{^{h → d H (ω, θ}} ) the absolute value of h ^→ _r (ω, θ) is _{^{h → d H (ω, θ}} ) h → d (ω, θ) sufficiently smaller than, the formula (19) If the second and third terms are ignored, the coherence γ (ω, θ) can be approximated as shown in Equation (23).

If _{^{h → d H (ω, θ}} ) h → d (ω, θ) even as ≠ 0, approximate coherence γ ~ (ω, θ) has a local minimum θ of equation (24). q is an arbitrary positive integer. Further, the range of q is limited for each frequency band.

  That is, the coherence can be suppressed not only in the direction given by Expression (16) but also in the direction given by Expression (24). If the coherence can be suppressed, the power of noise can be reduced, so that a sharp directivity can be realized as schematically shown in FIG.

2 schematically shows the difference in directivity between the case according to the principle of the present invention and the case according to the prior art. In FIG. 3, θ given by Expression (16) and Expression (24) are given. The difference in θ obtained will be specifically shown. ω = 2π × 1000 [rad / s], L = 0.70 [m], θ _s = π / 4 [rad]. FIG. 3 shows the direction dependency of the normalized coherence for comparison between the two, the direction indicated by the symbol ○ is θ given by the equation (16), and the direction indicated by the symbol + is It is (theta) given by Formula (24). As is apparent from FIG. 3, according to the prior art, the coherence becomes zero with respect to θ _s = π / 4 [rad] only in the direction indicated by the symbol ○, but according to the principle of the present invention. And θ _s = π / 4 [rad] and coherence is zero in many directions indicated by the symbol +, and in particular, θ _s = π / 4 [ Since the direction indicated by the symbol + exists in a direction much closer to rad], it can be understood that sharp directivity is realized as compared with the prior art.

As is apparent from the above description, the main feature of the present invention is that the transfer characteristic a ^→ (ω, θ) = [a ₁ (ω, θ),..., A _M (ω, θ)] ^T , for example, This is because the expression is expressed by the sum of the steering vector of the direct sound and the steering vector of a number of reflected sounds, as in Expression (17a). Accordingly, since the filter design concept itself is not affected, the filter W ^→ (ω, θ _s ) can be designed by a method other than the minimum variance distortionless response method.

A filter design method based on the S / N ratio maximization criterion and a filter design method based on power inversion will be described as methods other than the minimum variance distortion-free method. See Reference 2 for the filter design method based on the SNR maximization criterion and the filter design method based on power inversion.
(Reference 2) Nobuyoshi Kikuma, “Adaptive Antenna Technology”, 1st Edition, Ohm Corporation, 2003, pp.35-90

<1> Filter design method based on S / N ratio maximization criteria
In the filter design method based on the SN ratio maximization criterion, the filter W ^→ (ω, θ _s ) is determined based on the criterion for maximizing the SN ratio (SNR) in the target direction θ _s . The spatial correlation matrix of the audio object direction θ _s R _ss (ω), the spatial correlation matrix of the direction other than the target direction theta _s voice and R _nn (ω). At this time, the SNR is expressed by Expression (25). Note that R _ss (ω) is expressed by Expression (26), and R _nn (ω) is expressed by Expression (27). Transfer characteristic a ^→ (ω, θ _s ) = [a ₁ (ω, θ _s ),..., A _M (ω, θ _s )] ^T is expressed by equation (17a) (exactly, equation (17a ) Is θ _s ).

The filter W ^→ (ω, θ _s ) that maximizes the SNR in Expression (25) can be obtained by setting the gradient related to the filter W ^→ (ω, θ _s ) to zero, that is, Expression (28).

Thus, the filter W ^→ (ω, θ _s ) that maximizes the SNR in Expression (25) is given by Expression (29).

Expression (29) includes an inverse matrix of the spatial correlation matrix R _nn (ω) of speech in a direction other than the target direction θ _s , and the inverse matrix of R _nn (ω) is used as the speech in the target direction θ _s . It is known that it may be replaced with an inverse matrix of the spatial correlation matrix R _xx (ω) of the entire input including speech in directions other than the target direction θ _s . Note that R _xx (ω) = R _ss (ω) + R _nn (ω) = Q (ω) (see Expression (10a), Expression (26), and Expression (27)). That is, the filter W ^→ (ω, θ _s ) that maximizes the SNR in Expression (25) may be obtained by Expression (30).

<2> Filter design method based on power inversion In the filter design method based on power inversion, the filter W ^→ (ω, θ _s ) is determined. Here, as an example, it is assumed that the filter coefficient for the first microphone among the M microphones is fixed. In this design method, the filter W ^→ (ω, θ _s ) is omnidirectional (all the possible directions of arrival of speech) using the spatial correlation matrix R _xx (ω) under the constraint condition of Equation (32). It is designed to minimize the power of the voice in the direction (see equation (31)). Transfer characteristic a ^→ (ω, θ _s ) = [a ₁ (ω, θ _s ),..., A _M (ω, θ _s )] ^T is expressed by equation (17a) (exactly, equation (17a ) Is θ _s ). Note that R _xx (ω) = Q (ω) (see Expression (10a), Expression (26), and Expression (27)).

It is known that the filter W ^→ (ω, θ _s ), which is the optimal solution of the equation (31), is given by the equation (33) (see Reference 2).

<Embodiment>
The functional configuration and processing flow of the embodiment of the present invention are shown in FIGS. The narrow-directional speech enhancement apparatus 1 according to this embodiment includes an AD conversion unit 210, a frame generation unit 220, a frequency domain conversion unit 230, a filter application unit 240, a time domain conversion unit 250, a filter design unit 260, and a storage unit 290.

Step S1
In advance, the filter design unit 260 calculates a filter W ^→ (ω, θ _i ) for each frequency for each discrete direction that can be a target of speech enhancement. The total number of I discrete directions that may be subject to speech enhancement (I is 1 or more predetermined integer, satisfying the I ≦ P) _{^{When, W → (ω, θ 1}} ), ..., W → (ω, θ _i ),..., W ^→ (ω, θ _I ) (1 ≦ i ≦ I, ω∈Ω; i is an integer, Ω is a set of frequencies ω) is calculated in advance. For this purpose, transfer characteristic a ^→ (ω, θ _i ) = [a ₁ (ω, θ _i ), ..., a _M (ω, θ _i )] ^T (1 ≦ i ≦ I, ω∈Ω) It is necessary to obtain this information from the microphone array in the microphone array, the positional relationship of the reflectors such as the reflector, floor, wall, and ceiling with respect to the microphone array, the direct sound and the ξth (1 ≦ ξ ≦ Ξ) reflection. arrival time difference between the sounds can be specifically calculated based on the environment information, such as the reflectivity of the sound reflector by the formula (17a) (to be precise, in which a theta of formula (17a) was theta _i) . The number 反射 of the reflected sound is set to an integer satisfying 1 ≦ Ξ, but the value of Ξ is not particularly limited and may be appropriately set according to the calculation ability. When one reflector is installed in the vicinity of the microphone array, the transfer characteristic a ^→ (ω, θ _i ) can be specifically calculated by the equation (17b) (more precisely, θ in the equation (17b) is θ _i ). For the calculation of the steering vector, for example, Expression (14a), Expression (14b), Expression (18a), Expression (18b), Expression (18c), Expression (18d) can be used. In addition, you may use the transfer characteristic obtained by actual measurement in a real environment, for example, without depending on Formula (17a) and Formula (17b). Then, using the transfer characteristic a ^→ (ω, θ _i ), for example, W ^→ (ω, θ _i ) (1) according to any one of the equations (9), (29), (30), and (33). ≦ i ≦ I) is obtained. In addition, when using Formula (9), Formula (30), or Formula (33), the spatial correlation matrix Q (ω) (or R _xx (ω)) can be calculated by Formula (10b). When using equation (29), the spatial correlation matrix R _nn (ω) can be calculated by equation (27). I × | Ω | filters W ^→ (ω, θ _i ) (1 ≦ i ≦ I, ω∈Ω) are stored in the storage unit 290. | Ω | represents the number of elements of the set Ω.

Step S2
Sound is picked up using M microphones 200-1,..., 200-M constituting the microphone array. M is an integer of 2 or more.

There is no limit to the way the M microphones are arranged. However, by arranging M microphones two-dimensionally or three-dimensionally, there is an advantage that there is no uncertainty in the direction of voice enhancement. In other words, when M microphones are arranged in a straight line in the horizontal direction, for example, it is impossible to distinguish between voices coming from the front direction and voices coming from directly above. Can be prevented. In addition, in order to take a wide range of directions that can be set as the sound collection direction, the directivity of each microphone is a directivity capable of collecting sound with a certain sound pressure in a direction that can be the target direction θ _s that is the sound collection direction. It is better to have Therefore, a microphone having a relatively gentle directivity such as an omnidirectional microphone or a unidirectional microphone is preferable.

Step S3
The AD converter 210 converts an analog signal (sound collected signal) collected by the M microphones 200-1,..., 200-M into a digital signal x ^→ (t) = [x ₁ (t),. _M (t)] Convert to ^T. t represents a discrete time index.

Step S4
The frame generation unit 220 receives the digital signal x ^→ (t) = [x ₁ (t),..., X _M (t)] ^T output from the AD conversion unit 210 and stores N samples in a buffer for each channel. Thus, the digital signal x ^→ (k) = [x ^→ ₁ (k),..., X ^→ _M (k)] ^T is output in frame units. k is an index of the frame number. x ^→ _m (k) = [x _m ((k−1) N + 1),..., x _m (kN)] (1 ≦ m ≦ M). N depends on the sampling frequency, but in the case of 16kHz sampling, around 512 points is reasonable.

Step S5
The frequency domain transform unit 230 converts the digital signal x ^→ (k) of each frame into the frequency domain signal X ^→ (ω, k) = [X ₁ (ω, k),..., X _M (ω, k)] ^T Convert to and output. ω is an index of discrete frequency. One method for converting a time domain signal to a frequency domain signal is a fast discrete Fourier transform, but the present invention is not limited to this, and other methods for converting to a frequency domain signal may be used. The frequency domain signal X ^→ (ω, k) is output for each frequency ω and for each frame k.

Step S6
The filter application unit 240 changes the frequency domain signal X ^→ (ω, k) = [X ₁ (ω, k),..., X _M (ω, k)] ^T for each frequency ω∈Ω for each frame k. Then, by applying the filter W ^→ (ω, θ _s ) corresponding to the target direction θ _s to be emphasized, the output signal Y (ω, k, θ _s ) is output (see Expression (34)). Since the index s of the target direction θ _s is s∈ {1,..., I}, and the filter W ^→ (ω, θ _s ) is stored in the storage unit 290, for example, every time the process of step S6 is performed, The filter application unit 240 may acquire the filter W ^→ (ω, θ _s ) corresponding to the target direction θ _s to be emphasized from the storage unit 290. When the index s of the target direction θ _s does not belong to the set {1,..., I}, that is, when the filter W ^→ (ω, θ _s ) corresponding to the target direction θ _s is not calculated in the process of step S1. The filter design unit 260 may calculate the filter W ^→ (ω, θ _s ) corresponding to the target direction θ _s temporarily, or the filter W ^→ ( ^→ corresponding to the direction θ _{s ′} close to the target direction θ _s (ω, θ _{s ′} ) may be used.

Step S7
The time domain transform unit 250 transforms the output signal Y (ω, k, θ _s ) of each frequency ω∈Ω of the kth frame into the time domain to obtain a frame unit time domain signal y (k) of the kth frame. Further, the obtained frame unit time domain signal y (k) is connected in the order of the frame number index to output the time domain signal y (t) in which the voice in the target direction θ _s is emphasized. The method for converting the frequency domain signal into the time domain signal is an inverse transformation corresponding to the transformation method used in the process of step S5, for example, a fast discrete inverse Fourier transform.

Here, the embodiment in which the filter W ^→ (ω, θ _i ) is calculated in advance in the process of step S1 has been described, but the target direction θ _s is determined according to the calculation processing capability of the narrow directivity speech enhancement apparatus 1 and the like. An embodiment in which the filter design unit 260 calculates the filter W ^→ (ω, θ _s ) for each frequency after it is determined can also be adopted.

An experimental result according to an embodiment of the present invention (minimum dispersion no distortion response method) will be described. As shown in FIG. 6, 24 microphones are linearly arranged, and the reflector 300 is arranged so that the arrangement direction of the microphones included in the linear microphone array is a normal line of the reflector 300. Although there is no restriction | limiting in the shape of the reflecting plate 300, the reflecting surface is a plane, The flat reflecting plate which has a size of 1.0m x 1.0m, moderate thickness, and rigidity was used. The interval between adjacent microphones was 4 cm, and the reflectance α of the reflector 300 was 0.8. The target direction θ _s was set to 45 degrees. Assuming that the voice arrives at the linear microphone array as a plane wave, the transfer characteristic is calculated by equation (17b) (see equations (14a) and (18a)), and the directivity of the generated filter is verified. For comparison, two conventional methods (minimum dispersion no distortion response method without a reflector and delayed synthesis method with a reflector) were used.

The experimental results are shown in FIGS. Compared to the two conventional methods, it can be seen that the embodiment of the present invention can realize sharp directivity with respect to the target direction in any frequency band. In particular, the lower the frequency band, the better the utility of the present invention. FIG. 9 shows the directivity by the filter W ^→ (ω, θ) generated according to the embodiment of the present invention. FIG. 9 shows that not only the direct sound but also the reflected sound is emphasized.

As shown in FIG. 10, the case where the reflector 300 is arranged so that the angle formed by the arrangement direction of the microphones included in the linear microphone array and the plane of the reflector 300 is 45 degrees is the same as in the above-described experiment. The experiment was conducted. The target direction θ _s was set to 22.5 degrees, and other experimental conditions were the same as when the reflector 300 was arranged so that the arrangement direction of the microphones included in the linear microphone array was normal to the reflector 300.

  The experimental results are shown in FIGS. Compared to the two conventional methods, it can be seen that the embodiment of the present invention can realize sharp directivity with respect to the target direction in any frequency band. In particular, the lower the frequency band, the better the utility of the present invention.

  Next, exemplary embodiments of the present invention will be described with reference to FIGS. In these examples, the configuration of the microphone array is illustrated as a linear microphone array, but is not limited to the configuration of the linear microphone array.

  In the embodiment shown in FIG. 13, M microphones 200-1,..., 200-M constituting the linear microphone array are fixed to a rectangular flat plate-like support member 400, and in this state, sound collection of each microphone is performed. The holes are arranged on one plane (hereinafter referred to as an opening surface) of the support member 400 (M = 13 in the illustrated example). Note that wirings connected to the microphones 200-1,..., 200-M are not shown. The reflection plate 300 is fixed to the end of the support member 400 so that the arrangement direction of the microphones 200-1,..., 200-M is the normal line of the rectangular flat reflection plate 300. The opening surface of the support member 400 is a surface that forms 90 degrees with the reflector 300. In the embodiment configuration example shown in FIG. 13, the preferable property of the reflector 300 is the same as the property of the reflector described above, and the property of the support member 400 is not particularly limited, and each microphone 200-1,. It is sufficient to have a rigidity capable of firmly fixing 200-M.

  In the exemplary embodiment shown in FIG. 14A, the shaft portion 410 is fixed to the end portion of the support member 400, and the reflection plate 300 is rotatably attached to the shaft portion 410. According to this embodiment, it is possible to change the geometric arrangement of the reflector 300 with respect to the microphone array.

  In the embodiment configuration example shown in FIG. 14B, two reflectors 310 and 320 are further added to the embodiment configuration example shown in FIG. The properties of the two added reflectors 310 and 320 may be the same as or different from those of the reflector 300. The properties of the reflector 310 may be the same as or different from those of the reflector 320. Hereinafter, the reflection plate 300 is referred to as a fixed reflection plate 300. The shaft 510 is fixed to the end of the fixed reflector 300 (the end opposite to the end of the fixed reflector 300 fixed to the support member 400), and the reflector 310 is rotated around the shaft 510. It is attached movably. Further, the shaft portion 520 is fixed to the end portion of the support member 400 (the end portion opposite to the end portion of the support member 400 to which the fixed reflection plate 300 is fixed), and the reflection plate 320 is attached to the shaft portion 520. It is pivotally attached. Hereinafter, the reflectors 310 and 320 are referred to as the movable reflectors 310 and 320. 14B, for example, when the position of the movable reflecting plate 310 is set so that the reflecting surface of the fixed reflecting plate 300 and the reflecting surface of the movable reflecting plate 310 coincide with each other, the fixed reflecting plate 300 and the movable reflecting plate 300 are movable. The combination of the reflecting plates 310 can be made to function as a reflecting plate having a reflecting surface larger than that of the fixed reflecting plate 300. 14B, by setting the movable reflectors 310 and 320 to appropriate positions, for example, as shown in FIG. 15, the support member 400, the fixed reflector 300, and the movable reflector. Since the sound can be reflected many times in the space surrounded by 310 and 320, the number of reflected sounds can be controlled. In the case of the embodiment shown in FIG. 14B, the support member 400 serves as a reflector, and therefore preferably has the same properties as those of the reflector described above.

  16 differs from the embodiment shown in FIG. 13 in that the reflector 300 is also provided with a microphone array (linear microphone array in the example shown). In the embodiment shown in FIG. 16, the arrangement direction of the M microphones fixed to the support member 400 and the arrangement direction of the M ′ microphones fixed to the reflector 300 are on the same plane. The arrangement is not limited (M ′ = 13 in the illustrated example). For example, M ′ microphones may be fixed to the reflection plate 300 so as to have an arrangement direction orthogonal to the arrangement direction of M microphones fixed to the support member 400. According to the exemplary configuration shown in FIG. 16, the microphone array provided on the support member 400 and the reflector 300 (the microphone array provided on the reflector 300 is not used and the reflector 300 is used as a reflector). The present invention is implemented by a combination, or a combination of the support member 400 (the microphone array provided on the support member 400 is not used and the support member 400 is used as a reflector) and the microphone array provided on the reflector 300 The present invention can be implemented.

  Further, as an example of an extended implementation configuration of the implementation configuration example shown in FIG. 16, a configuration in which two reflectors 310 and 320 are further added to the implementation configuration example shown in FIG. It is good also as (refer FIG. 17). Although not shown, a microphone array may be provided on at least one of the movable reflectors 310 and 320. The sound collection holes of the microphones constituting the microphone array provided in the movable reflecting plate 310 are arranged, for example, on the plane (opening surface) of the movable reflecting plate 310 that can face the opening surface of the support member 400. The sound collecting holes of the microphones constituting the microphone array provided in the movable reflecting plate 320 are disposed on the plane (opening surface) of the movable reflecting plate 320 that can form the same plane as the opening surface of the support member 400, for example. Even such an example of the configuration can be used in the same manner as in the configuration example shown in FIG. Further, according to this embodiment, for example, when the position of the movable reflecting plate 320 is set so that the opening surface of the supporting member 400 and the opening surface of the movable reflecting plate 320 coincide with each other, the combination of the supporting member 400 and the movable reflecting plate 320 is changed. The microphone array can be made to function larger than the microphone array provided on the support member 400. Also in the embodiment configuration example shown in FIG. 17, in the embodiment configuration example in which at least one of the movable reflectors 310 and 320 is provided with a microphone array, the same usage pattern as that in the embodiment configuration example shown in FIG. Also in the example of the configuration shown in FIG. 17, in the example of the configuration in which the microphone array is provided on at least one of the movable reflectors 310 and 320, for example, the movable reflectors 310 and 320 are used as normal reflectors. It is also possible to use the microphone array provided on the support member 400 and the microphone array provided on the fixed reflector 300 as an integrated microphone array. In this case, this is equivalent to an embodiment in which a microphone array composed of (M + M ′) microphones and two reflectors are used.

  When the movable reflector 310 is provided with a microphone array, the sound collection holes of the microphones constituting the microphone array provided in the movable reflector 310 are opposite to the plane of the movable reflector 310 that can face the opening surface of the support member 400. A microphone array may be provided on the movable reflecting plate 310 so as to be arranged on the flat surface (opening surface). When the microphone array is provided on the movable reflector 320, the movable reflector 320 that can form the same plane as the opening surface of the support member 400 with the sound collection holes of the microphones constituting the microphone array provided on the movable reflector 320. A microphone array may be provided on the movable reflector 320 so as to be arranged on a plane (opening surface) opposite to the plane. Of course, a microphone array may be provided on the movable reflecting plate so that at least one of the movable reflecting plates 310 and 320 has an opening surface on both sides thereof.

[A] When the microphone array is provided on at least one of the movable reflectors 310 and 320, and the opening surface of the movable reflector 310 is a plane that can face the opening surface of the support member 400, or the movable reflector. When the opening surface of 320 is a flat surface that can form the same plane as the opening surface of the support member 400, in the usage mode shown in FIG. Although the apparent array size in the line-of-sight direction is reduced by disposing the movable reflector 310 and / or the movable reflector 320 so as not to be visible, the movable reflector 310 and / or the movable reflector 320 is provided. By using the microphone array, the same effect as when the array size is increased can be obtained.

[B] When the microphone array is provided on at least one of the movable reflectors 310 and 320, the opening surface of the movable reflector 310 is a plane opposite to the plane that can face the opening surface of the support member 400. If the opening surface of the movable reflecting plate 320 is a plane opposite to the plane that can form the same plane as the opening surface of the support member 400, in the usage mode shown in FIG. The same effect as when the array size is increased can be obtained while maintaining the size.

  When at least one of the movable reflectors 310 and 320 is provided with a microphone array on the movable reflector so as to have an opening surface on both sides, the effects of both [A] and [B] can be obtained. Is possible.

  As described above, it is one of the conditions that a narrow directivity beam can be generated by installing a flat reflector in the direction perpendicular to the arrangement direction of the linear microphone array. In the embodiment shown in FIGS. 16 and 17, since the microphones are deployed one-dimensionally, for example, when these microphones are arranged in the horizontal direction, the direction control in the horizontal angular direction is possible. There is, however, direction control in the elevation direction cannot be performed. Therefore, an embodiment in which an arbitrary direction in a three-dimensional space can be emphasized by developing the example of the embodiment configuration described in FIG. 17 in a three-dimensional manner will be described below. Referring to FIGS. 18 and 19, according to the third embodiment, the fixed reflector 300 and the support member 400 in the above-described embodiment configuration example of FIG. 17 are combined so as to form the opposite pyramid surfaces of the regular octagonal pyramid. The zoom microphone device 600 will be described. FIG. 18 is a front view of the zoom microphone device 600 according to the present embodiment. FIG. 19 is a side view of the zoom microphone device 600 according to the present embodiment. In the present embodiment, all of the fixed reflector 300 and the support member 400 that are referred to in FIG. 17 are collectively referred to as a fixed reflector. The configuration shown as the movable reflectors 310 and 320 in FIG. 17 is also called a movable reflector in this embodiment. The zoom microphone device 600 of this embodiment includes one support structure 601, eight fixed reflectors 611 to 618, eight fixed microphone arrays 621 to 628, eight movable reflectors 631 to 638, and eight. Movable microphone arrays 641 to 648, one central reflector 651, one central microphone array 661, eight hinges 671 to 678, eight supporting metal plates (large) 681 to 688, and eight supporting metals It consists of joining parts such as plates (small) 691-698 and bolts and screws. The support structure 601 is intended to instruct the fixed reflectors 611 to 618 and the central reflector 651 to be fixed at predetermined positions and orientations. The support structure 601 can be assembled using, for example, a die steel or a square steel pipe. The fixed reflecting plates 611 to 618 are trapezoidal flat plates and are made of a material having high reflectivity. For example, the fixed reflectors 611 to 618 can be made of wood having a thickness of about 1 cm, ABS resin material, or the like. The fixed microphone arrays 621 to 628 are configured such that a plurality of microphones are arranged in a straight line. In the present embodiment, the fixed microphone arrays 621 to 628 are arranged such that a plurality of microphones are aligned on the long plate-shaped support metal plates (large) 681 to 688 in a straight line in the longitudinal direction of the support metal plates (large) 681 to 688. And each microphone is fixed on a supporting metal plate (large) 681 to 688 with a joining member such as a bolt or a screw. The fixed reflectors 611 to 618 have fixed microphone arrays 621 to 628, and the surfaces of the fixed reflectors 611 to 628 are arranged so that the surfaces of the fixed reflectors 611 to 618 and the microphone arrangement directions of the fixed microphone arrays 621 to 628 are parallel to each other. One is attached to each. In this embodiment, each fixed reflector is provided with a plurality of small holes on a straight line. The plurality of small holes are arranged on the vertical bisector of the upper or lower base of the fixed reflector having a trapezoidal shape. With the sound receiving portions of the microphones of the fixed microphone arrays 621 to 628 arranged so as to look into the small holes, the supporting metal plates (large) 681 to 688 are fixed to the fixed reflecting plates 611 to 618 with a long bolt or the like. By attaching, the fixed microphone arrays 621 to 628 are fixed to the fixed reflecting plates 611 to 618. The fixed reflectors 611 to 618 are combined so as to form eight pyramidal surfaces of a regular octagonal pyramid whose opposing pyramidal surfaces are vertical, and their hypotenuses are joined. A regular octagonal flat plate-shaped central reflector 651 is arranged on the upper base of the regular octagonal pyramid, and the upper base of the trapezoidal fixed reflectors 611 to 618 is joined to each side of the central reflector 651. Yes. If the concave-side surface of the regular octagonal pyramid formed by the fixed reflecting plates 611 to 618 and the central reflecting plate 651 is a front surface and the convex-side surface is a back surface, the above-mentioned supporting metal plate (large) Numerals 681 to 688 are attached to the back surface side, which is the convex surface side, with long bolts, and the sound receiving portions of the microphones of the fixed microphone arrays 621 to 628 are small holes toward the front surface which is the concave surface side. It is assumed that it is exposed from. A regular octagonal pyramid formed by the fixed reflecting plates 611 to 618 and the central reflecting plate 651 is attached to a predetermined position of the support structure 601 in a predetermined direction. One hinge 671-678 is attached to each of the sides of the opening of the regular octagonal pyramid formed by the fixed reflectors 611-618 and the central reflector 651. In this embodiment, hinges 671 to 678 are hinges (for example, free stop hinges) that can be stopped at an arbitrary angle. Via the hinges 671 to 678, one movable reflecting plate 631 to 638 is attached to each side of the opening side of the regular octagonal truncated cone so as to be rotatable about the regular octagonal truncated cone opening end. In the present embodiment, the movable reflectors 631 to 638 are trapezoidal flat plates made of the same material as the fixed reflectors 611 to 618. The length of the lower base of the fixed reflectors 611 to 618 is equal to the length of the lower base of the fixed reflectors 631 to 638. The lower bases of the fixed reflectors 611 to 618 and the movable reflectors 631 to 638 are connected to each other via hinges 671 to 678. Since the hinges 671 to 678 are hinges that can be stopped at an arbitrary angle, the movable reflectors 631 to 638 can be manually changed in angle and can be maintained at the manually moved angle. Similar to the above-described fixed reflectors 611 to 618, the movable reflectors 631 to 638 are provided with small holes in a straight line on the vertical bisector of the upper or lower base. Movable microphone arrays 641 to 648 are attached to the movable reflectors 631 to 638. The movable microphone arrays 641 to 648 are arranged so that a plurality of microphones are arranged in a straight line in the longitudinal direction on the long support metal plates (small) 691 to 698 in the same manner as the fixed microphone arrays 621 to 628 described above. And it is comprised by fixing to support metal plate (small) 691-698. Similar to the fixed microphone arrays 621 to 628, the movable microphone arrays 641 to 648 are long with the supporting metal plates (small) 691 to 698 so that the sound receiving portions are exposed from the small holes toward the front surface on the concave side. It is attached to the movable reflectors 631 to 638 using bolts. The positions of the small holes provided in the respective reflecting plates are such that the movable reflecting plates 631 to 638 are rotated around the movable axis so that the concave reflecting plate surfaces of the movable reflecting plates 631 to 638 and the fixed reflecting plates 611 to 618 are arranged. When the plate surface on the concave side is in the same plane, the small holes provided in the movable reflector and the small holes provided in the fixed reflector connected thereto are arranged on the same straight line. It has been. A central microphone array 661 is attached to the central reflector 651 described above. The central microphone array 661 includes a support bar and a plurality of microphones. The support bar is formed by arranging a plurality of round holes penetrating in the radial direction of the round bar in the axial direction. The microphone is arranged and fixed in a round hole formed in the support rod. The central microphone array 661 configured as described above is a straight line whose support rod passes through the top vertex of the regular octagonal pyramid formed with the surfaces of the fixed reflectors 611 to 618 as the pyramidal surface and is perpendicular to the bottom surface of the regular octagonal pyramid. It is vertically attached to the front surface (concave surface side) of the central reflecting plate 651 so as to be disposed on the top.

  As described above, the positions of the movable reflecting plates 631 to 638 so that the reflecting surfaces (front surfaces) of the fixed reflecting plates 611 to 618 and the reflecting surfaces (front surfaces) of the movable reflecting plates 631 to 638 are arranged in the same plane. Is set, the combination of the fixed reflectors 611 to 618 and the movable reflectors 631 to 638 can function as a reflector having a larger reflection surface than the fixed reflectors 611 to 618. Furthermore, the sound that wraps around from the back surface can be blocked by the movable reflectors 631 to 638. Both of these are useful for creating an environment in which a narrow-directional beam can be easily generated. Further, by rotating and stationary the movable reflecting plates 631 to 638 to appropriate positions, as described in FIG. 15, the movable reflecting plates 631 to 638 are repeatedly performed in the space surrounded by the fixed reflecting plates 611 to 618 and the movable reflecting plates 631 to 638. Since sound can be reflected, the number of reflected sounds can be controlled, and sound can be collected with high energy. This is useful for creating an environment in which a beam having a narrow directivity is easily generated because a difference is easily generated between the target sound and the transfer characteristics of noise arriving from an angle having no arrival direction difference. In addition, with the above-described configuration, when the sound in the same direction as the sound from a specific direction is desired to be collected by distance, the height and angle of the regular octagonal pyramid may be adjusted. In the present embodiment, the central microphone array is arranged so as to be arranged on a straight line passing through the top of the regular octagonal pyramid formed with the surfaces of the fixed reflectors 611 to 618 as the pyramidal surface and perpendicular to the bottom of the regular octagonal pyramid. 661 is attached. This is to make the directivity characteristics of the zoom microphone device 600 more acute by utilizing the strength of directivity in the vertical direction, which is a characteristic of the linear microphone array.

[Modifications 1 to 5]
In the third embodiment, the zoom microphone device is shown in which the pyramidal surfaces facing each other of the regular octagonal pyramids are perpendicular to each other. However, the present invention is not limited to this. As described above, a flat reflector is installed perpendicular to the arrangement direction of the linear microphone array. If the direction can be controlled in the horizontal angle direction and the elevation angle direction, the shape of the fixed reflector is a regular octagonal pyramid. The arrangement of the pyramid surface is not necessarily required. Further, the movable reflectors 631 to 638 can be used to control the number of reflected sounds, but this is not essential. The central reflector 651 and the central microphone array 661 can be omitted as appropriate. Since the reflecting plates are preferably paired, it is desirable that the reflectors have a regular pyramid shape having a multiple of two pyramid surfaces or a regular pyramid shape. For example, a regular tetragonal pyramid (pedestal), a regular hexagonal pyramid (pedestal), and a regular octagonal pyramid (pedestal). In addition, if the number of reflectors is too large, such as regular hexagonal pyramids (tables), regular thirty-two square pyramids (tables), the energy of the reflected sound will be reduced. As the number of microphones decreases and the interval between the microphones becomes wider, the frequency band that can be controlled becomes narrower. If the number of microphones that can be used is about 16 to 96, the shape of a regular square pyramid (pedestal), regular hexagonal pyramid (pedestal), and regular octagonal pyramid (pedestal) is just right. Hereinafter, first to fifth modifications of the third embodiment will be described with reference to FIGS. FIG. 20 is a front view showing the configuration of the first modification of the present embodiment. FIG. 21 is a front view showing the configuration of the second modification of the present embodiment. FIG. 22 is a front view showing the configuration of the third modification of the present embodiment. FIG. 23 is a front view showing the configuration of the fourth modification of the present embodiment. FIG. 24 is a front view showing the configuration of the fifth modification of the present embodiment. The zoom microphone device 600a according to the first modification includes four fixed reflectors and four movable reflectors of the zoom microphone device 600 described above, and the fixed reflectors constitute a pyramidal surface of a regular quadrangular frustum. It is a combination. Similar to the zoom microphone device 600, the opposing pyramid surfaces are attached so as to be vertical. Also in this configuration, as in the zoom microphone device 600 described above, an arbitrary direction in the three-dimensional space can be emphasized. The zoom microphone device 600b according to the second modification has six fixed reflecting plates and six movable reflecting plates, respectively, of the zoom microphone device 600 described above, and the fixed reflecting plates form a pyramid surface of a regular hexagonal frustum. It is a combination. Similar to the zoom microphone device 600, the opposing pyramid surfaces are attached so as to be vertical. Also in this configuration, as in the zoom microphone device 600 described above, an arbitrary direction in the three-dimensional space can be emphasized. Further, as described above, the movable reflector, the central reflector, and the central microphone array are not essential components. Therefore, from the zoom microphone device 600a in the first modification, the movable reflector, the central reflector, and the central microphone array are omitted from the zoom microphone device 600c, and from the zoom microphone device 600b in the second modification to the movable reflector. The zoom microphone device 600d has a configuration in which the central reflector and the central microphone array are omitted, and the zoom microphone device 600e has a configuration in which the movable reflector, the central reflector, and the central microphone array are omitted from the zoom microphone device 600 in the third embodiment. As shown. Also in these zoom microphone devices 600c, 600d, and 600e, it is possible to realize a narrow-directional speech enhancement technique having sharper directivity than before.

<Application example>
The narrow-directional speech enhancement technique is useful for obtaining sound field information in more detail, corresponding to the generation of a clear image from a blurred image when expressed in an image. Examples of services in which the present invention is useful will be described below.

  A first example is content production combined with video. By using the embodiment of the present invention, it is possible to clearly emphasize a target sound in a distant place even in a noisy environment where there is a lot of noise (such as non-target sound). Corresponding audio can be added.

  As a second example, there is an application to a TV conference system (which may be an audio conference system). When conferencing in a small room, it was possible to emphasize the voice of the speaker using several microphones in the conventional technology as well, but in a large conference room (for example, 5 m or more away from the microphone) In a wide space where a speaker is present), it is difficult to clearly emphasize the voice of a distant speaker. For this reason, it is necessary to install a microphone in front of each speaker. However, by using the embodiment of the present invention, it is possible to clearly emphasize distant sounds, so a TV conference system corresponding to a large conference room can be constructed without installing a microphone in front of each speaker. It becomes possible to do.

Claims (4)

A zoom microphone device comprising one support structure, 2N fixed reflectors (N is an integer of 1 or more), and 2N microphone arrays in which a plurality of microphones are linearly arranged,
The microphone array is attached to the surface of the fixed reflector one by one so that the surface of the fixed reflector and the microphone array direction of the microphone array are parallel to each other,
The surfaces of the two fixed reflectors to which the microphone array is attached form 90 degrees, the microphone array direction of the microphone array attached to one fixed reflector, and the microphone array attached to the other fixed reflector N sets of fixed reflectors are formed by fixing the two fixed reflectors facing each other so that the microphone arrangement direction forms 90 degrees, and the N sets of fixed reflectors thus prepared are supported by the support structure. A zoom microphone device that is attached to the body. The zoom microphone device according to claim 1,
A movable reflector that is movable around a straight line formed by intersecting a plane perpendicular to the microphone array direction of the microphone array and a plane including the plate surface of the fixed reflector at the opening end of the N sets of fixed reflectors. A microphone array in which a plurality of microphones are linearly arranged on the movable reflector is attached so that a surface of the movable reflector and a microphone array direction of the microphone array are parallel to each other. age,
When the plate surface of the movable reflector and the plate surface of the fixed reflector are in the same plane,
The surface on which the microphone array of the movable reflector is attached and the surface on which the microphone array of the fixed reflector is attached are in the same direction,
A zoom microphone device, wherein a microphone array attached to the movable reflector and a microphone array attached to the fixed reflector are arranged on the same straight line. The zoom microphone device according to claim 1 or 2,
A zoom microphone apparatus, wherein the N sets of fixed reflectors are combined so as to form opposing pyramidal surfaces of a regular 2N pyramid. The zoom microphone device according to claim 3,
A zoom microphone apparatus comprising: a microphone array in which a plurality of microphones are linearly arranged on a straight line passing through the top of the regular 2N pyramid and perpendicular to the bottom surface of the regular 2N pyramid.

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