# Patent

## Title
Voiced sound interval detection device, voiced sound interval detection method and voiced sound interval detection program

## Abstract

This invention provides a voiced sound interval detection device which enables appropriate detection of a voiced sound interval of an observation signal even when a volume of sound from a sound source varies or when the number of sound sources is unknown or when different kinds of microphones are used together.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a National Stage of International Application No. PCT/JP2012/051554 filed Jan. 25, 2012, claiming priority based on Japanese Patent Application No. 2011-019815 filed Feb. 1, 2011, the contents of all of which are incorporated herein by reference in their entirety.
TECHNICAL FIELD
The present invention relates to a technique of detecting a voiced sound interval from voice signals, and more particularly, a voiced sound interval detection device which detects a voiced sound interval from voice signals collected by a plurality of microphones, and a voiced sound interval detection method and a voiced sound interval detection program therefor.
BACKGROUND ART
Numbers of techniques have been disclosed for classifying voiced sound intervals from voice signals collected by a plurality of microphones, one of which is recited, for example, in Patent Literature 1.
For correctly determining a voiced sound interval of each of a plurality of microphones, the technique recited in Patent Literature 1 includes firstly classifying each observation signal of each time frequency converted into a frequency domain on a sound source basis and making determination of a voiced sound interval or a voiceless sound interval with respect to each observation signal classified.
Shown in FIG. 5 is a diagram of a structure of a voiced sound interval classification device according to such background art as Patent Literature 1. Common voiced sound interval classification devices according to the background art include an observation signal classification unit 501, a signal separation unit 502 and a voiced sound interval determination unit 503.
Shown in FIG. 8 is a flow chart showing operation of a voiced sound interval classification device having such a structure according to the background art.
The voiced sound interval classification device according to the background art firstly receives input of a multiple microphone voice signal xm (f, t) obtained by time-frequency analysis by each microphone of voice observed by a number M of microphones (here, m denotes a microphone number, f denotes a frequency and t denotes time) and a noise power estimate λm (f) for each frequency of each microphone (Step S801).
Next, the observation signal classification unit 501 classifies a sound source with respect to each time frequency to calculate a classification result C (f, t) (Step S802).
Then, the signal separation unit 502 calculates a separation signal yn (f, t) of each sound source by using the classification result C (f, t) and the multiple microphone voice signal (Step S803).
Then, the voiced sound interval determination unit 503 makes determination of voiced sound or voiceless sound with respect to each sound source based on S/N (signal-noise ratio) by using the separation signal yn (f, t) and the noise power estimate λm (f) (Step S804).
Here, as shown in FIG. 6, the observation signal classification unit 501, which includes a voiceless sound determination unit 602 and a classification unit 601, operates in a manner as follows. Flow chart illustrating operation of the observation signal classification unit 501 is shown in FIG. 9.
First, an S/N ratio calculation unit 607 of the voiceless sound determination unit 602 receives input of the multiple microphone voice signal xm (f, t) and the noise power estimate λm, (f) to calculate an S/N ratio γm (f, t) for each microphone according to an Expression 1 (Step S901).




  
    
      
        
          
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Next, a nonlinear conversion unit 608 executes nonlinear conversion with respect to the S/N ratio for each microphone according to the following expression to calculate an S/N ratio Gm (f, t) as of after the nonlinear conversion (Step S902).

Gm(f,t)=γm(f,t)−ln γm(f,t)−1

Next, a determination unit 609 compares the predetermined threshold value η′ and S/N ratio Gm (f, t) of each microphone as of after the nonlinear conversion and when the S/N ratio Gm (f, t) as of after the nonlinear conversion is not more than the threshold value in each microphone, considers a signal at the time-frequency as noise to output C (f, t)=0 (Step S903). The classification result C (f, t) is cluster information which assumes a value from 0 to N.
Next, a normalization unit 603 of the classification unit 601 receives input of the multiple microphone voice signal xm (f, t) to calculate X′(f, t) according to the Expression 2 in an interval not determined to be noise (Step S904).




  
    
      
        
          
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X′(f, t) is a vector obtained by normalization by a norm of an M-dimensional vector having amplitude absolute values |xm (f, t)| of signals of M microphones.
Subsequently, a likelihood calculation unit 604 calculates a likelihood pn (X′(f, t)) n=1, . . . , N of a number N of speakers expressed by a Gaussian distribution having a mean vector determined in advance and a covariance matrix with a sound source model (Step S905).
Next, a maximum value determination unit 606 outputs n with which the likelihood pn (X′(f, t)) takes the maximum value as C (f, t)=n (Step S906).
Here, although the number of sound sources N and M may differ, n will take any value of 1, . . . , M because any of the microphones is assumed to be located near each of the N speakers as sound sources.
With a Gaussian distribution having a direction of each of M-dimensional coordinate axes as a mean vector as an initial distribution, a model updating unit 605 updates a sound source model by updating a mean vector and a covariance matrix by the use of a signal which is classified into its sound source model by using a speaker estimation result.
The signal separation unit 502 separates the applied multiple microphone voice signal xm (f, t) and the C (f, t) output by the observation signal classification unit 501 into a signal yn (f, t) for each sound source according to an Expression 3.




  
    
      
        
          
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Here, k (n) represents the number of a microphone closest to a sound source n which is calculated from a coordinate axis to which a Gaussian distribution of a sound source model is close.
The voiced sound interval determination unit 503 operates in a following manner.
The voiced sound interval determination unit 503 first obtains Gn (t) according to an Expression 4 by using the separation signal yn (f, t) calculated by the signal separation unit 502.




  
    
      
        
          
            
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Subsequently, the voiced sound interval determination unit 503 compares the calculated Gn (t) and a predetermined threshold value η and when Gn (t) is larger than the threshold value η, determines that time t is within a speech interval of the sound source n and when Gn (t) is not more than η, determines that time t is within a noise interval.
F represents a set of wave numbers to be taken into consideration and |F| represents the number of elements of the set F.
Patent Literature 1: Japanese Patent Laying-Open No. 2008-158035.
Non-Patent Literature 1: P. Fearnhead, “Particle Filters for Mixture Models with an Unknown Number of Components”, Statistics and Computing, vol 14, pp. 11-21, 2004.
Non-Patent Literature 2: B. A. Olshausen and D. J. Field, “Emergence of simple-cell receptive field properties by learning a sparse code for natural images”, Nature vol. 381, pp 607-609, 1996.
By the technique recited in the Patent Literature 1, for sound source classification executed by the observation signal classification unit 501, calculation is made assuming that a normalization vector X′ (f, t) is in a direction of a coordinate axis of a microphone close to a sound source.
In practice, however, since voice power always varies in a case, for example, where a sound source is a speaker, a normalization vector X′ (f, t) is far away from a coordinate axis direction of a microphone even when a sound source position does not shift at all, so that a sound source of an observation signal cannot be classified with enough precision.
Shown in FIG. 7 is a signal observed by two microphones, for example. Assuming now that a speaker close to a microphone number 2 makes a speech, voice power always varies in a space formed of observation signal absolute values of two microphones even if a sound source position has no change, so that the vector will vary on a bold line in FIG. 7.
Here, λ1 (f) and λ2 (f) each represent noise power whose square root is on the order of a minimum amplitude observed in each microphone.
At this time, although the normalization vector X′ (f, t) will be a vector constrained on a circular arc with a radius of 1, even when an observed amplitude of the microphone number 1 is approximately as small as a noise level and an observed amplitude of the microphone number 2 has a region larger enough than the noise level (i.e. γ2 (f, t) exceeds a threshold value η′ to consider the interval as a voiced sound interval), X′ (f, t) will largely derivate from the coordinate axis of the microphone number 2 (i.e. sound source direction) to fluctuate on the bold line in FIG. 7, thereby making classification of a sound source difficult and resulting in erroneously determining the voice interval of the microphone number 2 as a voiceless sound and deteriorating voice interval detection performance.
The technique recited in the Patent Literature 1 has another problem that since the number of sound sources is unknown in the observation signal classification unit 501, it is difficult for the likelihood calculation unit 604 to set a sound source model appropriate for sound source classification, so that a classification result will have an error, and as a result, voice interval detection performance will be deteriorated.
In a case, for example, where with two microphones and three sound sources (speakers), the third speaker is located near the middle point between the two microphones, sound sources cannot be appropriately classified by a sound source model close to the microphone axis. In addition, it is difficult to prepare a sound source model at an appropriate position apart from a microphone axis without advance-knowledge of the number of speakers, so that classification of a sound source of an observation signal is impossible and as a result, voice interval detection performance will be deteriorated.
When deterioration of an observation signal classification performance is caused by mixed use of different kinds of microphones without being calibrated, an amplitude value or a noise level varies with each microphone to have an increased effect, resulting in further deteriorating voice interval detection performance.
Object of the Invention
An object of the present invention is to solve the above-described problems and provide a voiced sound interval detection device which enables appropriate detection of a voiced sound interval of an observation signal even when a volume of sound from a sound source varies or when the number of sound sources is unknown or when different kinds of microphones are used together, and a voiced sound interval detection method and a voiced sound interval detection program therefor.
SUMMARY
According to a first exemplary aspect of the invention, a voiced sound interval detection device includes a vector calculation unit which calculates, from a power spectrum time series of voice signals collected by a plurality of microphones, a multidimensional vector series as a vector series of a power spectrum having as many dimensions as the number of the microphones, a clustering unit which clusters the multidimensional vector series, a voiced sound index calculation unit which calculates, at each time of the multidimensional vector series sectioned by an arbitrary time length, a center vector of a noise cluster and a center vector of a cluster to which a vector of the voice signal at the time in question belongs and after projecting the center vector of the noise cluster and the vector of the voice signal at the time in question toward a direction of the center vector of the cluster to which the vector of the voice signal at the time in question belongs, calculates a signal noise ratio as a voiced sound index, and a voiced sound interval determination unit which determines whether the vector of the voice signal is in a voiced sound interval or a voiceless sound interval by comparing the voiced sound index with a predetermined threshold value.
According to a second exemplary aspect of the invention, a voiced sound interval detection method of a voiced sound interval detection device which detects a voiced sound interval from voice signals collected by a plurality of microphones, includes a vector calculation step of calculating, from a power spectrum time series of voice signals collected by a plurality of microphones, a multidimensional vector series as a vector series of a power spectrum having as many dimensions as the number of the microphones, a clustering step of clustering the multidimensional vector series, a voiced sound index calculation step of calculating, at each time of the multidimensional vector series sectioned by an arbitrary time length, a center vector of a noise cluster and a center vector of a cluster to which a vector of the voice signal at the time in question belongs and after projecting the center vector of the noise cluster and the vector of the voice signal at the time in question toward a direction of the center vector of the cluster to which the vector of the voice signal at the time in question belongs, calculating a signal noise ratio as a voiced sound index, and a voiced sound interval determination step of determining whether the vector of the voice signal is in a voiced sound interval or a voiceless sound interval by comparing the voiced sound index with a predetermined threshold value.
According to a third exemplary aspect of the invention, a voiced sound interval detection program operable on a computer which functions as a voiced sound interval detection device that detects a voiced sound interval from voice signals collected by a plurality of microphones, which program causes the computer to execute a vector calculation processing of calculating, from a power spectrum time series of voice signals collected by a plurality of microphones, a multidimensional vector series as a vector series of a power spectrum having as many dimensions as the number of the microphones, a clustering processing of clustering the multidimensional vector series, a voiced sound index calculation processing of calculating, at each time of the multidimensional vector series sectioned by an arbitrary time length, a center vector of a noise cluster and a center vector of a cluster to which a vector of the voice signal at the time in question belongs and after projecting the center vector of the noise cluster and the vector of the voice signal at the time in question toward a direction of the center vector of the cluster to which the vector of the voice signal at the time in question belongs, calculating a signal noise ratio as a voiced sound index, and a voiced sound interval determination processing of determining whether the vector of the voice signal is in a voiced sound interval or a voiceless sound interval by comparing the voiced sound index with a predetermined threshold value.
The present invention enables appropriate detection of a voice interval of an observation signal even when a volume of sound from a sound source varies or when the number of sound sources is unknown or when different kinds of microphones are used together.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing a structure of a voiced sound interval detection device according to a first exemplary embodiment of the present invention;
FIG. 2 is a block diagram showing a structure of a voiced sound interval detection device according to a second exemplary embodiment of the present invention;
FIG. 3 is a diagram for use in explaining an effect of the present invention;
FIG. 4 is a diagram for use in explaining an effect of the present invention;
FIG. 5 is a block diagram showing a structure of a multiple microphone voice detection device according to background art;
FIG. 6 is a block diagram showing a structure of a multiple microphone voice detection device according to the background art;
FIG. 7 is a diagram for use in explaining a problem to be solved of a multiple microphone voice detection device according to the background art;
FIG. 8 is a flow chart showing operation of a multiple microphone voice detection device according to the background art;
FIG. 9 is a flow chart showing operation of a multiple microphone voice detection device according to the background art; and
FIG. 10 is a block diagram showing an example of a hardware configuration of a voiced sound interval detection device according to the present invention.



EXEMPLARY EMBODIMENT 
In order to clarify the foregoing and other objects, features and advantages of the present invention, exemplary embodiments of the present invention will be detailed in the following with reference to the accompanying drawings.
Other technical problems, means for solving the technical problems and functions and effects thereof other than the above-described objects of the present invention will become more apparent from the following disclosure of the exemplary embodiments. In all the drawings, like components are identified by the same reference numerals to omit description thereof as required.
First Exemplary Embodiment
First exemplary embodiment of the present invention will be detailed with reference to the drawings. In the following drawings, no description is made as required of a structure of a part not related to a gist of the present invention and no illustration is made thereof.
FIG. 1 is a block diagram showing a structure of a voiced sound interval detection device 100 according to the first exemplary embodiment of the present invention. With reference to FIG. 1, the voiced sound interval detection device 100 according to the present embodiment includes a vector calculation unit 101, a clustering unit 102, a voiced sound index calculation unit 103 and a voiced sound interval determination unit 106.
The vector calculation unit 101 receives input of a multiple microphone voice signal xm (f, t) (m=1, . . . , M) subjected to time-frequency analysis to calculate a vector S (f, t) of an M-dimensional power spectrum according to an Expression 5.




  
    
      
        
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Here, M represents the number of microphones.
The vector calculation unit 101 may also calculate a vector LS (f, t) of a logarithm power spectrum as shown in an Expression 6.




  
    
      
        
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The clustering unit 102 clusters the M-dimensional space vector calculated by the vector calculation unit 101.
When a vector S (f, 1:t) of an M-dimensional power spectrum of a frequency f from time 1 to t is obtained, the clustering unit 102 expresses a state of a number t of vector data clustered as zt. Unit of time is a signal sectioned by a predetermined time length.
h(zt) is assumed to be a function representing an arbitrary amount h which can be calculated from a system having a clustering state zt. The present exemplary embodiment is premised on that clustering is executed stochastically.
The clustering unit 102 is capable of calculating an expected value of h by integrating every clustering state zt with a post-distribution p(zt|S (f, 1:t)) multiplied according to a second member of an Expression 7.

Et[h]=∫h(zt)p(zt)|S(f,1:t))dzt≅Σi=1Lωtih(ztl)  (Expression 7)

In practice, however, an expected value is approximately calculated by taking a weighted sum by using a number L of clustering states zt1 (l=1, . . . , L) and their weights ωt1 as shown in a third member of the Expression 7.
Here, a clustering state zt1 represents how each of the number t of data is clustered. In a case of t=3, for example, every clustering combination of three data is possible, so that the clustering state zt1 will be five (L=5) sets represented by a set of cluster numbers including zt1={1, 1, 1}, zt2={1, 1, 2}, zt3={1, 2, 1}, zt4={1, 2, 2} and zt5={1, 2, 3}.
Assuming, for example, that a cluster center vector of data at time t is calculated as h (zt1), in the above case of t=3, with respect to the clustering state zt1, it will be obtained by calculating a post-distribution of each cluster included in a set of each zt1 as a Gaussian distribution having a conjugate advance-distribution to take a distribution mean value of clusters including data at time t=3.
Here, zt1 and ωt1 can be calculated by applying a particle filter method to a Dirichlet Process Mixture model, details of which are recited in, for example, Non-Patent Literature 1.
L=1 means crucial clustering and this case can be also considered to be included.
The voiced sound index calculation unit 103 calculates an expected value G (f, t) of G (zt1) shown in the Expression 8 as the above-described h( ) at the clustering unit 102 to calculate an index of a voiced sound.




  
    
      
        
          
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Here, Q in the Expression 8 represents a cluster center vector at time t in zt1, A represents a center vector having the smallest cluster center among clusters included in zt1 and S is abridged notation of S (f, t) with “•” representing an inner product.
γ in the Expression 8 corresponds to an S/N ratio calculated by projecting a noise power vector Λ and a power spectrum S each in a direction of a cluster center vector in the clustering state ztl. More specifically, G is a result obtained by expanding the following expression into M-dimensional space:

Gm(f,t)=γm(f,t)−ln γm(f,t)−1.

The voiced sound interval determination unit 106 compares the G (f, t) calculated by the voiced sound index calculation unit 103 and a predetermined threshold value η and when G (f, t) is larger than the threshold value η, determines that time t is within a speech interval and when G (f, t) is not more than the threshold value η, determines that time t is within a noise interval.
Effects of the First Exemplary Embodiment
Next, effects of the present exemplary embodiment will be described.
In the present exemplary embodiment, the clustering unit 102 clusters an M-dimensional space vector calculated by the vector calculation unit 101. This realizes clustering reflecting variation of a volume of sound from a sound source.
In a case of observation by two microphones as shown in FIG. 3, for example, when a speaker is making a speech near a microphone number 2, clustering executed in a certain clustering state zt1 includes a cluster 1 near a noise vector Λ (f, t), a cluster 2 in a region where the sound volume of a microphone 1 is small and a cluster 3 in a region where the same is larger.
Here, it is not necessary to determine the number of clusters in advance because taking into consideration the clustering state zt1 having various numbers of clusters, these clustering states are stochastically handled.
In the present exemplary embodiment, when the power spectrum S (f, t) at each time is applied, the voiced sound index calculation unit 203 calculates a voiced sound index G (f, t) in a direction of a cluster center vector to which its data belongs.
This produces an effect of being less subject to effects caused by a difference between microphones because even when different kinds of microphones are used together, that is, even when a power spectrum value or a noise level on each microphone axis differs, clustering is executed in an M-dimensional space to calculate a cluster center vector realized taking effects of data variation into consideration and evaluate a voiced sound index in its direction.
In addition, since the voiced sound interval determination unit 106 determines a voiced sound interval by using thus calculated voiced sound index, appropriate detection of a voice interval of an observation signal is possible even when a volume of sound from a sound source varies or when the number of sound sources is unknown or when different kinds of microphones are used together.
Although a sound source in the present invention is assumed to be voice, it is not limited thereto but allows other sound source such as sound of an instrument.
Second Exemplary Embodiment
Next, a second exemplary embodiment of the present invention will be detailed with reference to the drawings. In the following drawings, no description is made as required of a structure of a part not related to a gist of the present invention and no illustration is made thereof.
FIG. 2 is a block diagram showing a structure of a voiced sound interval detection device 100 according to the second exemplary embodiment of the present invention.
The voiced sound interval detection device 100 according to the present exemplary embodiment comprises a difference calculation unit 104 and a sound source direction estimation unit 105 in addition to the components of the first exemplary embodiment shown in FIG. 1.
The difference calculation unit 104 calculates an expected value ΔQ (f, t) of ΔQ (zt1) shown in an Expression 9 as h ( ) in the clustering unit 102 and calculates a direction of fluctuation of the cluster center.




  
    
      
        
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Here, the Expression 9 represents a result obtained by standardizing a cluster center vector difference Qt−Qt-1 including data at time t and t−1 by their mean norm |Qt+Qt-1|/2.
The sound source direction estimation unit 105 calculates a base vector φ(i) and a coefficient ai (f, t) that make I the smallest by using data of fεF, tετ of ΔQ (f, t) according to the following expression.

I(a,φ)=ΣfεF,tετ[Σm{Qm(f,t)−Σiai(f,t)φm(i)}2]+ξΣi|ai(f,t)|]

Next, as a sound source direction D (f, t), the sound source direction estimation unit 105 estimates a base vector which makes a, (f, t) the largest at each f, t according to the following expression.

D(f,t)=φj,j=argmaxiai(f,t)

“φ” and “a” which make I the smallest can be calculated by alternately applying the steepest descent method to “a” and “φ”, details of which are recited, for example, in the Non-Patent Literature 2.
Here, F represents a set of wave numbers to be taken into consideration, τ represents a buffer width preceding and succeeding predetermined time t. In order to reduce instability of a sound source direction, it is possible to use a buffer width allowed to vary so as not to include a region determined as a noise interval by the voiced sound interval determination unit 106 with tε{t−τ1, . . . , t+τ2}.
In addition, since as long as the number of base vectors is set to be sufficient number, a coefficient a of an unnecessary base vector goes 0, so that it is unnecessary to know the number of sound sources in advance.
The voiced sound interval determination unit 106 calculates a sum Gj (t) of voiced sound indexes G (f, t) of frequencies classified into respective sound sources φj by using the voiced sound index G (f, t) calculated by the voiced sound index calculation unit 103 and the sound source direction D (f, t) estimated by the sound source direction estimation unit 105 according to an Expression 10.




  
    
      
        
          
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Next, the voiced sound interval determination unit 106 compares a predetermined threshold value η and the calculated Gj (t) and when Gj (t) is larger than the threshold value η, determines that the sound source direction is within a speech interval of the sound source φj.
When Gj (t) is not more than the threshold value η, determine that the sound source direction is in a noise interval.
Effects of the Second Exemplary Embodiment
Next, effects of the present exemplary embodiment will be described.
In the present exemplary embodiment, when a vector S (f, t) of a power spectrum at each time is applied, the difference calculation unit 104 calculates a differential vector ΔQ (f, t) of a cluster center to which data of the time calculated by the clustering unit 102 and data of preceding time belong. Even when a volume of sound from a sound source varies, this produces an effect of allowing ΔQ (f, t) to indicate a sound source direction substantially accurately without being affected by the variation.
Difference between clusters will be expressed by, for example, a vector indicated by a bold dot line as shown in FIG. 4, which shows that the vector indicates a sound source direction.
In addition, from the ΔQ (f, t) calculated by the difference calculation unit 104, the sound source direction estimation unit 105 calculates its main components while allowing them to be non-orthogonal and exceed a space dimension. Here, it is unnecessary to know the number of sound sources in advance and neither necessary is designating an initial sound source position. Even when the number of sound sources is unknown, the effect of calculating a sound source direction can be obtained.
In addition, since the voiced sound interval determination unit 106 determines a voiced sound interval by using these calculated voiced sound index and sound source direction, even when a volume of sound from a sound source varies or when the number of sound sources is unknown or when different kinds of microphones are used together, observation signal sound source classification and voice interval detection can be appropriately executed.
Next, an example of a hardware configuration of the voiced sound interval detection device 100 of the present invention will be described with reference to FIG. 10. FIG. 10 is a block diagram showing an example of a hardware configuration of the voiced sound interval detection device 100.
With reference to FIG. 10, the voiced sound interval detection device 100, which has the same hardware configuration as that of a common computer device, comprises a CPU (Central Processing Unit) 801, a main storage unit 802 formed of a memory such as a RAM (Random Access Memory) for use as a data working region or a data temporary saving region, a communication unit 803 which transmits and receives data through a network, an input/output interface unit 804 connected to an input device 805, an output device 806 and a storage device 807 to transmit and receive data, and a system bus 808 which connects each of the above-described components with each other. The storage device 807 is realized by a hard disk device or the like which is formed of a non-volatile memory such as a ROM (Read Only Memory), a magnetic disk or a semiconductor memory.
The vector calculation unit 101, the clustering unit 102, the difference calculation unit 104, the sound source direction estimation unit 105, the voiced sound interval determination unit 106 and the voiced sound index calculation unit 103 of the voiced sound interval detection device 100 according to the present invention have their operation realized not only in hardware by mounting a circuit part which is a hardware part such as an LSI (Large Scale Integration) with a program incorporated but also in software by storing a program which provides the function in the storage device 807, loading the program into the main storage unit 802 and executing the same by the CPU 801.
Hardware configuration is not limited to those described above.
While the invention has been particularly shown and described with reference to exemplary embodiments thereof, the invention is not limited to these embodiments. It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the claims.
An arbitrary combination of the foregoing components and conversion of the expressions of the present invention to/from a method, a device, a system, a recording medium, a computer program and the like are also available as a mode of the present invention.
In addition, the various components of the present invention need not always be independent from each other, and a plurality of components may be formed as one member, or one component may be formed by a plurality of members, or a certain component may be a part of other component, or a part of a certain component and a part of other component may overlap with each other, or the like.
While the method and the computer program of the present invention have a plurality of procedures recited in order, the order of recitation is not a limitation to the order of execution of the plurality of procedures. When executing the method and the computer program of the present invention, therefore, the order of execution of the plurality of procedures can be changed without hindering the contents.
Moreover, execution of the plurality of procedures of the method and the computer program of the present invention are not limitedly executed at timing different from each other. Therefore, during the execution of a certain procedure, other procedure may occur, or a part or all of execution timing of a certain procedure and execution timing of other procedure may overlap with each other, or the like.
Furthermore, a part or all of the above-described exemplary embodiments can be recited as the following claims but are not to be construed limitative.
The whole or part of the exemplary embodiments disclosed above can be described as, but not limited to, the following supplementary notes.
INDUSTRIAL APPLICABILITY
The present invention is applicable to such use as speech interval detection for executing recognition of voice collected by using multiple microphones.

## Claims

1. A voiced sound interval detection device comprising:
circuitry configured to:
calculate, from a power spectrum time series of voice signals collected by a plurality of microphones, a multidimensional vector series as a vector series of a power spectrum having as many dimensions as the number of said microphones;
cluster said multidimensional vector series;
calculate, at each time of said multidimensional vector series sectioned by an arbitrary time length, a center vector of a noise cluster and a center vector of a cluster to which a vector of said voice signal at the time in question belongs and after projecting the center vector of said noise cluster and the vector of said voice signal at the time in question toward a direction of the center vector of the cluster to which the vector of said voice signal at the time in question belongs, calculate a signal noise ratio as a voiced sound index; and
determine whether the vector of said voice signal is in a voiced sound interval or a voiceless sound interval by comparing said voiced sound index with a predetermined threshold value for executing voice recognition of the voice signals collected by the plurality of microphones.

2. The voiced sound interval detection device according to claim 1, wherein said circuitry executes stochastic clustering, and
calculates an expected value of said voiced sound index from said clustering result.

3. The voiced sound interval detection device according to claim 1, wherein said multidimensional vector series is a vector series of a logarithm power spectrum.

4. A voiced sound interval detection method of a voiced sound interval detection device which detects a voiced sound interval from voice signals collected by a plurality of microphones, comprising: by circuitry,
calculating, from a power spectrum time series of voice signals collected by a plurality of microphones, a multidimensional vector series as a vector series of a power spectrum having as many dimensions as the number of said microphones;
clustering said multidimensional vector series; a voiced sound index calculation step of calculating, at each time of said multidimensional vector series sectioned by an arbitrary time length, a center vector of a noise cluster and a center vector of a cluster to which a vector of said voice signal at the time in question belongs and after projecting the center vector of said noise cluster and the vector of said voice signal at the time in question toward a direction of the center vector of the cluster to which the vector of said voice signal at the time in question belongs, calculating a signal noise ratio as a voiced sound index; and
determining whether the vector of said voice signal is in a voiced sound interval or a voiceless sound interval by comparing said voiced sound index with a predetermined threshold value for executing voice recognition of the voice signals collected by the plurality of microphones.

5. The voiced sound interval detection method according to claim 4, wherein stochastic clustering, and
calculating an expected value of said voiced sound index from said clustering result.

6. The voiced sound interval detection method according to claim 4, wherein said multidimensional vector series is a vector series of a logarithm power spectrum.

7. A storage device storing a voiced sound interval detection program operable on a computer which functions as a voiced sound interval detection device that detects a voiced sound interval from voice signals collected by a plurality of microphones, wherein said voiced sound interval detection program causes said computer to execute:
a vector calculation processing of calculating, from a power spectrum time series of voice signals collected by a plurality of microphones, a multidimensional vector series as a vector series of a power spectrum having as many dimensions as the number of said microphones;
a clustering processing of clustering said multidimensional vector series;
a voiced sound index calculation processing of calculating, at each time of said multidimensional vector series sectioned by an arbitrary time length, a center vector of a noise cluster and a center vector of a cluster to which a vector of said voice signal at the time in question belongs and after projecting the center vector of said noise cluster and the vector of said voice signal at the time in question toward a direction of the center vector of the cluster to which the vector of said voice signal at the time in question belongs, calculating a signal noise ratio as a voiced sound index; and
a voiced sound interval determination processing of determining whether the vector of said voice signal is in a voiced sound interval or a voiceless sound interval by comparing said voiced sound index with a predetermined threshold value for executing voice recognition of the voice signals collected by the plurality of microphones.

8. The storage device according to claim 7, wherein
said clustering processing includes stochastic clustering, and
said voiced sound index calculation processing includes calculating an expected value of said voiced sound index from said clustering result.

9. The storage device according to claim 7, wherein said multidimensional vector series is a vector series of a logarithm power spectrum.