Abstract:
With conventional source separator devices, specific frequency bands are significantly reduced in environments where dispersed static is present that does not come from a particular direction, and as a result, the dispersed static may be filtered irregularly without regard to sound source separation results, giving rise to musical noise. In an embodiment of the present invention, by computing weighting coefficients which are in a complex conjugate relation, for post-spectrum analysis output signals from microphones ( 10, 11 ), a beam former unit ( 3 ) of a sound source separator device ( 1 ) thus carries out a beam former process for attenuating each sound source signal that comes from a region wherein the general direction of a target sound source is included and a region opposite to said region, in a plane that intersects a line segment that joins the two microphones ( 10, 11 ). A weighting coefficient computation unit ( 50 ) computes a weighting coefficient on the basis of the difference between power spectrum information calculated by power calculation units ( 40, 41 ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a sound source separation device, a sound source separation method, and a program which use a plurality of microphones and which separate, from signals having a plurality of acoustic signals mixed, such as a plurality of voice signals output by a plurality of sound sources, and various environmental noises, a sound source signal arrived from a target sound source. 
       BACKGROUND ART 
       [0002]    When it is desired to record particular voice signals in various environments, the surrounding environment has various noise sources, and it is difficult to record only the signals of a target sound through a microphone. Accordingly, some noise reduction process or sound source separation process is necessary. 
         [0003]    An example environment that especially needs those processes is an automobile environment. In an automobile environment, because of the popularization of cellular phones, it becomes typical to use a microphone placed distantly in the automobile for a telephone call using the cellular phone during driving. However, this significantly deteriorates the telephone speech quality because the microphone has to be located away from speaker&#39;s mouth. Moreover, an utterance is made in the similar condition when a voice recognition is performed in the automobile environment during driving. This is also a cause of deteriorating the voice recognition performance. Because of the advancement of the recent voice recognition technology, with respect to the deterioration of the voice recognition rate relative to stationary noises, most of the deteriorated performance can be recovered. It is, however, difficult for the recent voice recognition technology to address the deterioration of the recognition performance for simultaneous utterance by a plurality of utterers. According to the recent voice recognition technology, the technology of recognizing mixed voices of two persons simultaneously uttered is poor, and when a voice recognition device is in use, passengers other than an utterer are restricted so as not to utter, and thus the recent voice recognition technology restricts the action of the passengers. 
         [0004]    Moreover, according to the cellular phone or a headset which is connected to the cellular phone to enable a hands-free call, when a telephone call is made under a background noise environment, the deterioration of the telephone speech quality also occurs. 
         [0005]    In order to solve the above-explained technical issue, there are sound source separation methods which use a plurality of microphones. For example, Patent Document 1 discloses a sound source separation device which performs a beamformer process for attenuating respective sound source signals arrived from a direction symmetrical to a vertical line of a straight line interconnecting two microphones, and extracts spectrum information of the target sound source based on a difference in pieces of power spectrum. information calculated for a beamformer output. 
         [0006]    When the sound source separation device of Patent Document 1 is used, the characteristic having the directivity characteristics not affected by the sensitivity of the microphone element is realized, and it becomes possible to separate a sound source signal from the target sound source from mixed sounds containing mixed sound source signals output by a plurality of sound sources without being affected by the variability in the sensitivity between the microphone elements. 
       PRIOR ART DOCUMENT 
     Patent Document 
       [0000]    
       
         Patent Document 1: Japan Patent No. 4225430 
       
     
       Non-Patent Documents 
       [0000]    
       
         Non-patent Document 1: Y. Ephraim and D. Malah, “Speech enhancement using minimum mean-square error short-time spectral amplitude estimator”, IEEE Trans Acoust., Speech, Signal Processing, ASSP-32, 6, pp. 1109-1121, December 1984. 
         Non-patent Document 2: S. Gustafsson, P. Jax, and P. Vary, “A novel psychoacoustically motivated audio enhancement algorithm preserving background noise characteristics”, IEEE International Conference on Acoustics, Speech and Signal Processing, ICASSP &#39;98, vol. 1, ppt. 397-400 vol. 1, 12-15 May 1998. 
       
     
       SUMMARY OF THE INVENTION 
     Problem to be Solved 
       [0010]    According to the sound source separation device of Patent Document 1, however, when the difference between two pieces of power spectrum information calculated after the beamformer process is equal to or greater than a predetermined threshold, the difference is recognized as the target sound, and is directly output as it is. Conversely, when the difference between the two pieces of power spectrum information is less than the predetermined threshold, the difference is recognized as noises, and the output at the frequency band of those noises is set to be 0. Hence, when, for example, the sound source separation device of Patent Document 1 is activated in diffuse noise environments having an arrival direction uncertain like a road noises, a certain frequency band is largely cut. As a result, the diffuse noises are irregularly sorted into sound source separation results, becoming musical noises. Note that musical noises are the residual of canceled noises, and are isolated components over a time axis and a frequency axis. Accordingly, such musical noises are heard as unnatural and dissonant sounds. 
         [0011]    Moreover, Patent Document 1 discloses that diffuse noises and stationary noises are reduced by executing a post-filter process before the beamformer process, thereby suppressing a generation of musical noises after the sound source separation. However, when a microphone is placed at a remote location or when a microphone is molded on a casing of a cellular phone or a headset, etc., the difference in sound level of noises input to both microphones and the phase difference thereof become large. Hence, if the gain obtained from the one microphone is directly applied to another microphone, the target sound may be excessively suppressed for each band, or noises may remain largely. As a result, it becomes difficult to sufficiently suppress a generation of musical noises. 
         [0012]    The present invention has been made in order to solve the above-explained technical issues, and it is an object of the present invention to provide a sound source separation device, a sound source separation method, and a program which can sufficiently suppress a generation of musical noises without being affected by the placement of microphones. 
       Solution to the Problem 
       [0013]    To address the above technical issues, an aspect of the present invention provides a sound source separation device that separates, from mixed sounds containing mixed sound source signals output by a plurality of sound sources, a sound source signal from a target sound source, the sound source separation device includes: a first beamformer processing unit that performs, in a frequency domain using respective first coefficients different from each other, a product-sum operation on respective output signals by a microphone pair comprising two microphones into which the mixed sounds are input to attenuate a sound source signal arrived from a region opposite to a region including a direction of the target sound source with a plane intersecting with a line interconnecting the two microphones being as a boundary; a second beamformer processing unit which multiplies respective output signals by the microphone pair by a second coefficient in a relationship of complex conjugate with the first coefficients different from each other in the frequency domain, and which performs a product-sum operation on an obtained result in the frequency domain to attenuate a sound source signal arrived from the region including the direction of the target sound source with the plane being as the boundary; a power calculation unit which calculates first spectrum information having a power value for each frequency from a signal obtained through the first beamformer processing unit, and which further calculates second spectrum information having a power value for each frequency from a signal obtained through the second beamformer processing unit; a weighting-factor calculation unit that calculates, in accordance with a difference in the power values for each frequency between the first spectrum information and the second spectrum information, a weighting factor for each frequency to be multiplied by the signal obtained through the first beamformer processing unit; and a sound source separation unit that separates, from the mixed sounds, the sound source signal from the target sound source based on a multiplication result of the signal obtained through the first beamformer processing unit by the weighting factor calculated by the weighting-factor calculation unit. 
         [0014]    Moreover, another aspect of the present invention provides a sound source separation method executed by a sound source separation device comprising a first beamformer processing unit, a second beamformer processing unit, a power calculation unit, a weighting-factor calculation unit, and a sound source separation unit, the method includes: a first step of causing the first beamformer processing unit to perform, in a frequency domain using respective first coefficients different from each other, a product-sum operation on respective output signals by a microphone pair comprising two microphones into which mixed sounds containing mixed sound signals output by a plurality of sound sources are input to attenuate a sound source signal arrived from a region opposite to a region including a direction of a target sound source with a plane intersecting with a line interconnecting the two microphones being as a boundary; a second step of causing the second beamformer processing unit to multiply respective output signals by the microphone pair by a second coefficient in a relationship of complex conjugate with the first coefficients different from each other in the frequency domain, and to perform a product-sum operation on an obtained result in the frequency domain to attenuate a sound source signal arrived from the region including the direction of the target sound source with the plane being as the boundary; a third step of causing the power calculation unit to calculate first spectrum information having a power value for each frequency from a signal obtained through the first step, and to further calculate second spectrum information having a power value for each frequency from a signal obtained through the second step; a fourth step of causing the weighting-factor calculation unit to calculate, in accordance with a difference in the power values for each frequency between the first spectrum information and the second spectrum information, a weighting factor for each frequency to be multiplied by the signal obtained through the first step; and a fifth step of causing the sound source separating unit to separate, from the mixed sounds, a sound source signal from the target sound source based on a multiplication result of the signal obtained through the first step by the weighting factor calculated through the fourth step. 
         [0015]    Furthermore, the other aspect of the present invention provides a sound source separation program that causes a computer to execute: a first process step of performing, in a frequency domain using respective first coefficients different from each other, a product-sum operation on respective output signals by a microphone pair comprising two microphones into which mixed sounds containing mixed sound signals output by a plurality of sound sources are input to attenuate a sound source signal arrived from a region opposite to a region including a direction of a target sound source with a plane intersecting with a line interconnecting the two microphones being as a boundary; a second process step of multiplying respective output signals by the microphone pair by a second coefficient in a relationship of complex conjugate with the first coefficients different from each other in the frequency domain, and performing a product-sum operation on an obtained result in the frequency domain to attenuate a sound source signal arrived from the region including the direction of the target sound source with the plane being as the boundary; a third process step of calculating first spectrum information having a power value for each frequency from a signal obtained through the first process step, and further calculating second spectrum information having a power value for each frequency from a signal obtained through the second process step; a fourth process step of calculating, in accordance with a difference in the power values for each frequency between the first spectrum information and the second spectrum information, a weighting factor for each frequency to be multiplied by the signal obtained through the first process step; and a fifth process step of separating, from the mixed sounds, a sound source signal from the target sound source based on a multiplication result of the signal obtained through the first process step by the weighting factor calculated through the fourth process step. 
         [0016]    According to those configurations, the generation of musical noises can be suppressed in an environment where, in particular, diffusible noises are present, while at the same time, the sound source signal from the target sound source can be separated from mixed sounds containing mixed sound source signals output by the plurality of sound sources. 
       Advantageous Effects of the Invention 
       [0017]    It becomes possible to sufficiently suppress a generation of musical noises while maintaining the effect of Patent Document 1. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a diagram showing a configuration of a sound source separation system according to a first embodiment; 
           [0019]      FIG. 2  is a diagram showing a configuration of a beamformer unit according to the first embodiment; 
           [0020]      FIG. 3  is a diagram showing a configuration of a power calculation unit; 
           [0021]      FIG. 4  is a diagram showing process results of microphone input signals by the sound source separation device of Patent Document 1 and the sound source separation device according to the first embodiment of the present invention; 
           [0022]      FIG. 5  is an enlarged view of apart of the process results shown in  FIG. 4 ; 
           [0023]      FIG. 6  is a diagram showing a configuration of noise estimation unit; 
           [0024]      FIG. 7  is a diagram showing a configuration of a noise equalizer; 
           [0025]      FIG. 8  is a diagram showing another configuration of the sound source separation system according to the first embodiment; 
           [0026]      FIG. 9  is a diagram showing a configuration of a sound source separation system according to a second embodiment; 
           [0027]      FIG. 10  is a diagram showing a configuration of a control unit; 
           [0028]      FIG. 11  is a diagram showing an example configuration of a sound source separation system according to a third embodiment; 
           [0029]      FIG. 12  is a diagram showing an example configuration of the sound source separation system according to the third embodiment; 
           [0030]      FIG. 13  is a diagram showing an example configuration of the sound source separation system according to the third embodiment; 
           [0031]      FIG. 14  is a diagram showing a configuration of a sound source separation system according to a fourth embodiment; 
           [0032]      FIG. 15  is a diagram showing a configuration of a directivity control unit; 
           [0033]      FIG. 16  is a diagram showing directivity characteristics of the sound source separation device of the present invention; 
           [0034]      FIG. 17  is a diagram showing another configuration of the directivity control unit; 
           [0035]      FIG. 18  is a diagram showing directivity characteristics of the sound source separation device of the present invention when provided with a target sound correcting unit; 
           [0036]      FIG. 19  is a flowchart showing an example process executed by the sound source separation system; 
           [0037]      FIG. 20  is a flowchart showing the detail of a process by the noise estimation unit; 
           [0038]      FIG. 21  is a flowchart showing the detail of a process by the noise equalizer; 
           [0039]      FIG. 22  is a flowchart showing the detail of a process by a residual-noise-suppression calculation unit; 
           [0040]      FIG. 23  is a diagram showing a graph for a comparison between near-field sound and far-field sound with respect to an output value by a beamformer  30  (microphone pitch: 3 cm); 
           [0041]      FIG. 24  is a diagram showing a graph for a comparison between near-field sound and far-field sound with respect to an output value by the beamformer  30  (microphone pitch: 1 cm); 
           [0042]      FIG. 25  is a diagram showing an interface of sound source separation by the sound source separation device of Patent Document 1; and 
           [0043]      FIG. 26  is a diagram showing the directivity characteristics of the sound source separation device of Patent Document 1. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0044]    Embodiments of the present invention will now be explained with reference to the accompanying drawings. 
       First Embodiment 
       [0045]      FIG. 1  is a diagram showing a basic configuration of a sound source separation system according to a first embodiment. This system includes two micro-phones (hereinafter, referred to as “microphones”)  10  and  11 , and a sound source separation device  1 . The explanation will be given below for the embodiment in which the number of the microphones is two, but the number of the microphones is not limited to two as long as at least equal to or greater than two microphones are provided. 
         [0046]    The sound source separation device  1  includes hardware, not illustrated, such as a CPU which controls the whole sound source separation device and which executes arithmetic processing, a ROM, a RAM, and a storage device like a hard disk device, and also software, not illustrated, including a program and data, etc., stored in the storage device. Respective functional blocks of the sound source separation device  1  are realized by those hardware and software. 
         [0047]    The two microphones  10  and  11  are placed on a plane so as to be distant from each other, and receive signals output by two sound sources R 1  and R 2 . At this time, those two sound sources R 1  and R 2  are each located at two regions (hereinafter, referred to as “right and left of a separation surface”) divided with a plane (hereinafter, referred to as separation surface) intersecting with a line interconnecting the two microphones  10  and  11 , but that the sound sources are not necessarily positioned at symmetrical locations with respect to the separation surface. According to this embodiment, the explanation will be given of an example case in which the separation surface is a plane intersecting with a plane containing therein the line interconnecting the two microphones  10  and  11  at right angle, and is a plane passing through the midpoint of the line. 
         [0048]    It is presumed that the sound output by the sound source R 1  is a target sound to be obtained, and the sound output by the sound source R 2  is noises to be suppressed (the same is true throughout the specification). The number of noises is not limited to one, and multiple numbers of noises may be suppressed. However, it is presumed that the direction of the target sound and those of the noises are different. 
         [0049]    The two sound source signals obtained from the microphones  10  and  11  are subjected to frequency analysis for each microphone output by spectrum analysis units  20  and  21 , respectively, and in a beamformer unit  3 , the signals having undergone the frequency analysis are filtered by beamformers  30  and  31 , respectively, having null-points formed at the right and left of the separation surface. Power calculation units  40  and  41  calculate respective powers of filter outputs. Preferably, the beamformers  30  and  31  have null-points formed symmetrically with respect to the separation surface in the right and left of the separation surface. 
         [0050]    (Beamformer Unit) 
         [0051]    First, with reference to  FIG. 2 , an explanation will be given of the beamformer unit  3  configured by the beamformers  30  and  31 . With signals x 1 (ω) and x 2 (ω) decomposed for each frequency component by the spectrum analysis unit  20  and the spectrum analysis unit  21 , respectively, being as input, multipliers  100   a ,  100   b ,  100   c , and  100   d  respectively perform multiplication with filter coefficients w 1 (ω),w 2 (ω),w 1 *(ω), and w 2 *(ω) (where * indicates a relationship of complex conjugate). 
         [0052]    Adders  100   e  and  100   f  add respective two multiplication results and output filtering process results ds 1 (ω) and ds 2 (ω) as respective outputs. Provided that a gain with respect to a target direction θ 1  is 1, a filter vector of the beamformer  30  forming a null-point in another direction θ 2  is W 1 (ω, θ 1 , θ 2 )=[w 1 (ω, θ 1 , θ 2 ) w 2 (ω, θ 1 , θ 2 )] T , and an observation signal is X(ω, θ 1 , θ 2 )=[x 1 (ω, θ 1 , θ 2 ), x 2 (ω, θ 1 , θ 2 )] T , the output ds 1 (ω) of the beamformer  30  can be obtained from a following formula where T indicates a transposition operation, and H indicates a conjugate transposition operation. 
         [0000]        ds   1 (ω)= W   1 (ω,θ 1 ,θ 2 ) H   X (ω,θ 1 θ 2 )  (1)
 
         [0053]    Moreover, when a filter vector of the beamformer  31  is W 2 (ω, θ 1 , θ 2 )=[w 1 * (*ω, θ 1 , θ 2 ), w 2 * (ω, θ 1 , θ 2 )] T , the output ds 2 (ω) of the beamformer  31  can be obtained from a following formula. 
         [0000]        ds   2 (ω)= W   2 (ω,θ 1 ,θ 2 ) H   X (ω,θ 1 θ 2 )  (2)
 
         [0054]    The beamformer unit  3  uses the complex conjugate filter coefficients, and forms null-points at symmetrical locations with respect to the separation surface in this manner. Note that ω indicates an angular frequency, and satisfies a relationship ω=2πf with respect to a frequency f. 
         [0055]    (Power Calculation Unit) 
         [0056]    Next, an explanation will be given of power calculation units  40  and  41  with reference to  FIG. 3 . The power calculation units  40  and  41  respectively transform the outputs ds 1 (ω) and ds 2 (ω) of the beamformer  30  and the beamformer  31  into pieces of power spectrum information ps 1 (ω) and ps 2 (ω) through following calculation formulae. 
         [0000]        ps   1 (ω)=[ Re ( ds   1 (ω))] 2   +[Im ( ds   1 (ω))] 2   (3)
 
         [0000]        ps   2 (ω)=[ Re ( ds   2 (ω))] 2   +[Im ( ds   2 (ω))] 2   (4)
 
         [0057]    (Weighting-Factor Calculation Unit) 
         [0058]    Respective outputs ps 1 (ω) and ps 2 (ω) of the power calculation units  40  and  41  are used as two inputs into a weighting-factor calculation unit  50 . The weighting-factor calculation unit  50  outputs a weighting factor G BSA (ω) for each frequency with the pieces of power spectrum information that are the outputs by the two beamformers  30  and  31  being as inputs. 
         [0059]    The weighting factor G BSA (ω) is a value based on a difference between the pieces of the power spectrum information, and as an example weighting factor G BSA (ω), an output value of a monotonically increasing function having a domain of a value which indicates, when a difference between ps 1 (ω) and ps 2 (ω) is calculated for each frequency, and the value of ps 1 (ω) is larger than that of ps 2 (ω), a value obtained by dividing the square root of the difference between ps 1 (ω) and ps 2 (ω) by the square root of ps 1 (ω), and which also indicates 0 when the value of ps 1 (ω) is equal to or smaller than that of ps 2 (ω). When the weighting factor G BSA (ω) is expressed as a formula, a following formula can be obtained. 
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         [0060]    In the formula (5), max(a, b) means a function that returns a larger value between a and b. Moreover, F(x) is a weakly increasing function that satisfies dF(x)/dx≧0 in a domain x≧0, and examples of such a function are a sigmoid function and a quadratic function. 
         [0061]    G BSA (ω)ds 1 (ω) will now be discussed. As is indicated by the formula (1), ds 1 (ω) is a signal obtained through a linear process on the observation signal X(ω, θ 1 , θ 2 ). On the other hand, G BSA (ω)ds 1 (ω) is a signal obtained through a non-linear process on ds 1 (ω). 
         [0062]      FIG. 4A  shows an input signal from a microphone,  FIG. 4B  shows a process result by the sound source separation device of Patent Document 1, and  FIG. 4C  shows a process result by the sound source separation device of this embodiment. That is,  FIGS. 4B and 4C  show example G BSA (ω) ds 1 (ω) through a spectrogram. For the monotonically increasing function F(x) of the sound source separation device of this embodiment, a sigmoid function was applied. In general, a sigmoid function is a function expressed as 1/(1+exp(a−bx)), and in the process result shown in  FIG. 4C , a=4 and b=6. 
         [0063]    Moreover,  FIG. 5  is an enlarged view showing a part (indicated by a number  5 ) of the spectrogram of  FIGS. 4A to 4C  in a given time slot in an enlarged manner in the time axis direction. When a spectrogram indicating a process result ( FIG. 5B ) of the input sound ( FIG. 5A ) by the sound source separation device of Patent Document 1 is observed, it becomes clear that energies of noise components are eccentrically located in the time direction and the frequency direction in comparison with the process result ( FIG. 5C ) by the sound source separation device of this embodiment, and musical noises are generated. 
         [0064]    In contrast, with respect to the noise components of the spectrogram of  FIG. 4C , unlike the input signal, the energies of the noise components are not eccentrically located in the time direction and the frequency direction, and musical noises are little. 
         [0065]    (Musical-Noise-Reduction-Gain Calculation Unit) 
         [0066]    G BSA (ω) dS 1 (ω) is a sound source signal from a target sound source and having the musical noises sufficiently reduced, but in the cases of noises like diffusible noises arrived from various directions, G BSA (ω) that is a non-liner process has a value largely changing for each frequency bin or for each frame, and is likely to generate musical noises. Hence, the musical noises are reduced by adding a signal before the non-linear process having no musical noises to the output after the non-linear process. More specifically, a signal is calculated which is obtained by adding a signal X BSA  (ω) obtained by multiplying the output ds 1 (ω) of the beamformer  30  by the output G BSA (ω) and the output ds 1 (ω) of the beamformer  30  at a predetermined ratio. 
         [0067]    Moreover, there is another method which recalculates a gain for multiplication of the output ds 1 (ω) of the beamformer  30 . The musical-noise-reduction-gain calculation unit  60  recalculates a gain G S (ω) for adding a signal X BSA (ω) obtained by multiplying the output ds 1 (ω) of the beamformer  30  by the output G BSA (ω) of the weighting-factor calculation unit  50  and the output ds 1 (ω) of the beamformer  30  at a predetermined ratio. 
         [0068]    A result (X S (ω)) obtained by mixing X BSA (ω) with the output ds 1 (ω) of the beamformer  30  at a certain ratio can be expressed by a following formula. Note that γ S  is a weighting factor setting the ratio of mixing, and is a value larger than 0 and smaller than 1. 
         [0000]        X   s (ω)=γ S   X   BSA (ω)+(1−γ S ) ds   1 (ω)  (6)
 
         [0069]    Moreover, when the formula (6) is expanded to a form of multiplying the output ds 1 (ω) of the beamformer  30  by the gain, a following formula can be obtained. 
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         [0070]    That is, the musical-noise-reduction-gain calculation unit  60  can be configured by a subtractor that subtracts 1 from G BSA (ω), a multiplier that multiplies the subtraction result by the weighting factor γ s , and an adder that adds 1 to the multiplication result. That is, according to such configuration, the gain value G S (ω) having the musical noises reduced is recalculated as a gain to be multiplied by the output ds 1 (ω) of the beamformer  30 . 
         [0071]    A signal obtained based on the multiplication result of the gain value G S (ω) and the output ds 1 (ω) of the beamformer  30  is a sound source signal from the target sound source and having the musical noises reduced in comparison with G BSA (ω) ds 1 (ω). This signal is transformed into a time domain signal by a time-waveform transformation unit  120  to be discussed later, and may output as a sound source signal from the target sound source. 
         [0072]    Meanwhile, since the gain value G S (ω) becomes always larger than G BSA (ω), musical noises are reduced, while at the same time, the noise components are increased. Hence, in order to suppress residual noises, a residual-noise-suppression-gain calculation unit  110  is provided at the following stage of the musical-noise-reduction-gain calculation unit  60 , and a further optimized gain value is recalculated. 
         [0073]    Moreover, the residual noises of X S (ω) obtained by multiplying the output ds 1 (ω) of the beamformer  30  by the gain G S (ω) calculated by the musical-noise-reduction-gain calculation unit  60  contain non-stationary noises. Hence, in order to enable estimation of such non-stationary noises, in a calculation of estimated noises utilized by the residual-noise-suppression-gain calculation unit  110 , a blocking matrix unit  70  and a noise equalizer  100  to be discussed later are applied. 
         [0074]    (Noise Estimation Unit) 
         [0075]      FIGS. 6A to 6D  are block diagrams of a noise estimation unit  70 . The noise estimation unit  70  performs adaptive filtering on the two signals obtained through the microphones  10  and  11 , and cancels the signal components that are the target sound from the sound source R 1 , thereby obtaining only the noise components. 
         [0076]    It is presumed that a signal from the sound source R 1  is S(t). The sound from the sound source R 1  reaches the microphone  10  faster than the sound from the sound source R 2 . It is also presumed that signals of sounds from other sound sources are n j (t), and those are defined as noises. At this time, an input x 1 (t) of the microphone  10  and an input x 2 (t) of the microphone  11  can be expressed as follows. 
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                     1 
                   
                   ) 
                 
               
             
             
               
                 
                   
                     
                       x 
                       2 
                     
                      
                     
                       ( 
                       t 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         h 
                         
                           s 
                            
                           
                               
                           
                            
                           2 
                         
                       
                        
                       
                         s 
                          
                         
                           ( 
                           t 
                           ) 
                         
                       
                     
                     + 
                     
                       
                         ∑ 
                         
                           j 
                           = 
                           1 
                         
                         K 
                       
                        
                       
                           
                       
                        
                       
                         
                           h 
                           
                             nj 
                              
                             
                                 
                             
                              
                             2 
                           
                         
                          
                         
                           
                             n 
                             j 
                           
                            
                           
                             ( 
                             t 
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     9 
                     - 
                     2 
                   
                   ) 
                 
               
             
           
         
       
     
         [0000]    where: 
         [0077]    h s1  is a transfer function of the target sound to the microphone  10 ; 
         [0078]    h s2  is a transfer function of the target sound to the microphone  11 ; 
         [0079]    h nj1  is a transfer function of noises to the microphone  10 ; and 
         [0080]    h nj2  is a transfer function of noises to the microphone  11 . 
         [0081]    An adaptive filter  71  shown in  FIG. 6  convolves the input signal of the microphone  10  with an adaptive filtering coefficient, and calculates pseudo signals similar to the signal components obtained through the microphone  11 . Next, a subtractor  72  subtracts the pseudo signal from the signal from the microphone  11 , and calculates an error signal (a noise signal) in the signal from the sound source R 1  and included in the microphone  11 . An error signal x ABM (t) is the output signal by the noise estimation unit  70 . 
         [0000]        x   ABM ( t )= x   2 ( t )− H   T ( t )· x   1 ( t )  (10)
 
         [0082]    Furthermore, the adaptive filter  71  updates the adaptive filtering coefficient based on the error signal. For example, NLMS (Normalized Least Mean Square) is applied for the updating of an adaptive filtering coefficient H(t). Moreover, the updating of the adaptive filter may be controlled based on an external VAD (Voice Activity Detection) value or information from a control unit  160  to be discussed later ( FIGS. 6C and 6D ). More specifically, for example, when a threshold comparison unit  74  determines that the control signal from the control unit  160  is larger than a predetermined threshold, the adaptive filtering coefficient H(t) may be updated. Note that a VAD value is a value indicating whether or not a target voice is in an uttering condition or from a non-uttering condition. Such a value may be a binary value of On/Off, or may be a probability value having a certain range indicating the probability of an uttering condition. 
         [0083]    At this time, if the target sound and noises are non-correlated, the output x ABM (t) of the noise estimation unit  70  can be calculated as follow. 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       x 
                       ABM 
                     
                      
                     
                       ( 
                       t 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         ∑ 
                         
                           j 
                           = 
                           1 
                         
                         K 
                       
                        
                       
                           
                       
                        
                       
                         
                           h 
                           
                             nj 
                              
                             
                                 
                             
                              
                             2 
                           
                         
                          
                         
                           
                             n 
                             j 
                           
                            
                           
                             ( 
                             t 
                             ) 
                           
                         
                       
                     
                     - 
                     
                       
                         
                           H 
                           T 
                         
                          
                         
                           ( 
                           t 
                           ) 
                         
                       
                       · 
                       
                         
                           ∑ 
                           
                             j 
                             = 
                             1 
                           
                           K 
                         
                          
                         
                             
                         
                          
                         
                           
                             h 
                             
                               nj 
                                
                               
                                   
                               
                                
                               1 
                             
                           
                            
                           
                             
                               n 
                               j 
                             
                              
                             
                               ( 
                               t 
                               ) 
                             
                           
                         
                       
                     
                     + 
                     
                       
                         
                           ( 
                           
                             
                               
                                 h 
                                 
                                   s 
                                    
                                   
                                       
                                   
                                    
                                   2 
                                 
                               
                                
                               
                                 h 
                                 
                                   s 
                                    
                                   
                                       
                                   
                                    
                                   1 
                                 
                                 
                                   - 
                                   1 
                                 
                               
                             
                             - 
                             
                               H 
                                
                               
                                 ( 
                                 t 
                                 ) 
                               
                             
                           
                           ) 
                         
                         T 
                       
                        
                       
                         h 
                         
                           s 
                            
                           
                               
                           
                            
                           1 
                         
                       
                        
                       
                         s 
                          
                         
                           ( 
                           t 
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   11 
                   ) 
                 
               
             
           
         
       
     
         [0084]    At this time, if a transfer function which suppresses the target sound can be estimated, the output x ABM (t) can be expressed as follow. 
         [0085]    (It is presumed that a transfer function H(t)→h s2 h s1   −1  which suppresses a target sound can be estimated.) 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       x 
                       ABM 
                     
                      
                     
                       ( 
                       t 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         ∑ 
                         
                           j 
                           = 
                           1 
                         
                         K 
                       
                        
                       
                           
                       
                        
                       
                         
                           h 
                           
                             nj 
                              
                             
                                 
                             
                              
                             2 
                           
                         
                          
                         
                           
                             n 
                             j 
                           
                            
                           
                             ( 
                             t 
                             ) 
                           
                         
                       
                     
                     - 
                     
                       
                         ( 
                         
                           
                             h 
                             
                               s 
                                
                               
                                   
                               
                                
                               2 
                             
                           
                            
                           
                             h 
                             
                               s 
                                
                               
                                   
                               
                                
                               1 
                             
                             
                               - 
                               1 
                             
                           
                         
                         ) 
                       
                        
                       
                         τ 
                         · 
                         
                           
                             ∑ 
                             
                               j 
                               = 
                               1 
                             
                             K 
                           
                            
                           
                               
                           
                            
                           
                             
                               h 
                               
                                 nj 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                              
                             
                               
                                 n 
                                 i 
                               
                                
                               
                                 ( 
                                 t 
                                 ) 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   12 
                   ) 
                 
               
             
           
         
       
     
         [0086]    According to the above-explained operations, the noise components from directions other than the target sound direction can be estimated to some level. In particular, unlike the Griffith-Jim technique, no fixed filter is used, and thus the target sound can be suppressed robustly depending on a difference in the microphone gain. Moreover, as shown in  FIGS. 6B to 6D , by changing a DELAY value of the filter in a delay device  73 , the spatial range where sounds are determined as noises becomes controllable. Accordingly, it becomes possible to narrow down or expand the directivity depending on the DELAY value. 
         [0087]    As the adaptive filter, in addition to the above-explained filter, ones which are robust to the difference in the gain characteristic of the microphone can be used. 
         [0088]    Moreover, with respect to the output by the noise estimation unit  70 , a frequency analysis is performed by a spectrum analysis unit  80 , and power for each frequency bin is calculated by a noise power calculation unit  90 . Moreover, the input to the noise estimation unit  70  may be a microphone input signal having undergone a spectrum analysis. 
         [0089]    (Noise Equalizer) 
         [0090]    The noise quantity contained in X ABM (ω) obtained by performing a frequency analysis on the output by the noise estimation unit  70  and the noise quantity contained in the signal X S (ω) obtained by adding the signal X BSA (ω) which is obtained by multiplying the output ds 1 (ω) of the beamformer  30  by the weighting factor G BSA (ω) and the output ds 1 (ω) of the beamformer  30  at a predetermined ratio have a similar spectrum but have a large difference in the energy quantity. Hence, the noise equalizer  100  performs correction so as to make both energy quantities consistent with each other. 
         [0091]      FIG. 7  is a block diagram of the noise equalizer  100 . The explanation will be given of an example case in which, as inputs to the noise equalizer  100 , an output pX ABM (ω) of the power calculation unit  90 , an output G S (ω) of the musical-noise-reduction-gain calculation unit  60 , and the output ds 1 (ω) of the beamformer  30  are used. 
         [0092]    First, a multiplier  101  multiplies ds 1 (ω) by G S (ω). A power calculation unit  102  calculates the power of the output by such a multiplier. Smoothing units  103  and  104  perform smoothing process on the output pX ABM (ω) of the power calculation unit  90  and an output pX S (ω) of the power calculation unit  102  in an interval where sounds are determined as noises based on the external VAD value and upon reception of a signal from the control unit  160 . The “smoothing process” is a process of averaging data in successive pieces of data in order to reduce the effect of data largely different from other pieces of data. According to this embodiment, the smoothing process is performed using a primary IIR filter, and an output pX′ ABM (ω) of the power calculation unit  90  and an output pX′ S (ω) of the power calculation unit  102  both having undergone the smoothing process are calculated based on the output pX ABM (ω)) of the power calculation unit  90  and the output pX S (ω) of the power calculation unit  102  in the currently processed frame with reference to the output by the power calculation unit  90  and the output by the power calculation unit  102  having undergone the smoothing process in a past frame. As an example smoothing process, the output pX′ ABM (ω) of the power calculation unit  90  and the output pX′ S (ω) of the power calculation unit  102  both having undergone the smoothing process are calculated as a following formula (13-1). In order to facilitate understanding for a time series, a processed frame number m is used, and it is presumed that a currently processed frame is m and a processed frame right before is m−1. The process by the smoothing unit  103  may be executed when a threshold comparison unit  105  determines that the control signal from the control unit  160  is smaller than a predetermined threshold. 
         [0000]        pX′   S (ω, m )=α· pX′   S (ω, m− 1)+(1−α)· pX   S (ω, m )  (13-1)
 
         [0000]        pX′   ABM (ω, m )=α· pX′   ABM (ω, m− 1)+(1−α)· pX   ABM (ω, m )  (13-2)
 
         [0093]    An equalizer updating unit  106  calculates an output ratio between pX′ ABM (ω) and pX′ S (ω). That is, the output by the equalizer updating unit  106  becomes as follow. 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       H 
                       EQ 
                     
                      
                     
                       ( 
                       
                         ω 
                         , 
                         m 
                       
                       ) 
                     
                   
                   = 
                   
                     
                       
                         
                           pX 
                           S 
                           ′ 
                         
                          
                         
                           ( 
                           
                             ω 
                             , 
                             m 
                           
                           ) 
                         
                       
                        
                       
                           
                       
                     
                     
                       
                         pX 
                         ABM 
                         ′ 
                       
                        
                       
                         ( 
                         
                           ω 
                           , 
                           m 
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   14 
                   ) 
                 
               
             
           
         
       
     
         [0094]    An equalizer adaptation unit  107  calculates power pλ d (ω) of the estimated noises contained in X S (ω) based on an output H EQ (ω) of the equalizer updating unit  106  and the output pX ABM (ω) of the power calculation unit  90 . pλ d (ω) can be calculated based on, for example, a following calculation. 
         [0000]        pλ   d (ω)= H   EQ (ω)· pX   ABM (ω)  (15)
 
         [0095]    (Residual-Noise-Suppression-Gain Calculation Unit) 
         [0096]    The residual-noise-suppression-gain calculation unit  110  recalculates a gain to be multiplied to ds 1 (ω) in order to suppress noise components residual when the gain value G S (ω) is applied to the output ds 1 (ω) of the beamformer  30 . That is, the residual-noise-suppression-gain calculation unit  110  calculates a residual noise suppression gain G T (ω) that is a gain for appropriately eliminating the noise components contained in X S (ω) based on an estimated value λ d (ω) of the noise components with respect to the value X S (ω) obtained by applying G S (ω) to ds 1 (ω). For calculation of the gain, a Wiener filter or an MMSE-STSA technique (see Non-patent Document 1) are widely applied. According to the MMSE-STSA technique, however, it is assumed that noises are in a normal distribution, and non-stationary noises, etc., do not match the assumption of MMSE-STSA in some cases. Hence, according to this embodiment, an estimator that is relatively likely to suppress non-stationary noises is used. However, any techniques are applicable to the estimator. 
         [0097]    The residual-noise-suppression-gain calculation unit  110  calculates the gain G T (ω) as follows. First, the residual-noise-suppression-gain calculation unit  110  calculates an instant Pre-SNR (a ratio of clean sound and noises (S/N))) derived based on a post-SNR (S+N)/N). 
         [0000]    
       
         
           
             
               
                 
                   
                     γ 
                      
                     
                       ( 
                       ω 
                       ) 
                     
                   
                   = 
                   
                     max 
                     ( 
                     
                       
                         
                           
                             
                                
                               
                                 
                                   X 
                                   S 
                                 
                                  
                                 
                                   ( 
                                   ω 
                                   ) 
                                 
                               
                                
                             
                             2 
                           
                           
                             p 
                              
                             
                                 
                             
                              
                             
                               
                                 λ 
                                 d 
                               
                                
                               
                                 ( 
                                 ω 
                                 ) 
                               
                             
                           
                         
                         - 
                         1 
                       
                       , 
                       0 
                     
                     ) 
                   
                 
               
               
                 
                   ( 
                   16 
                   ) 
                 
               
             
           
         
       
     
         [0098]    Next, the residual-noise-suppression-gain calculation unit  110  calculates a pre-SNR (a ratio of clean sound and noises (S/N))) through DECISION-DIRECTED APPROACH. 
         [0000]    
       
         
           
             
               
                 
                   
                     ξ 
                      
                     
                       ( 
                       
                         ω 
                         , 
                         m 
                       
                       ) 
                     
                   
                   = 
                   
                     
                       
                         α 
                         · 
                         
                           
                              
                             
                               
                                 X 
                                 S 
                               
                                
                               
                                 ( 
                                 
                                   ω 
                                   , 
                                   
                                     m 
                                     - 
                                     1 
                                   
                                 
                                 ) 
                               
                             
                              
                           
                           2 
                         
                       
                       
                         p 
                          
                         
                             
                         
                          
                         
                           
                             λ 
                             d 
                           
                            
                           
                             ( 
                             ω 
                             ) 
                           
                         
                       
                     
                     + 
                     
                       
                         ( 
                         
                           1 
                           - 
                           α 
                         
                         ) 
                       
                       · 
                       
                         γ 
                          
                         
                           ( 
                           ω 
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   17 
                   ) 
                 
               
             
           
         
       
     
         [0099]    Subsequently, the residual-noise-suppression-gain calculation unit  110  calculates an optimized gain based on the pre-SNR. β P (ω) in a following formula (18) is a spectral floor value that defines the lower limit value of the gain. By setting this to be a large value, the sound quality deterioration of the target sound can be suppressed but the residual noise quantity increases. Conversely, if setting is made to have a small value, the residual noise quantity decreases but the sound quality deterioration of the target sound increases. 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       G 
                       P 
                     
                      
                     
                       ( 
                       ω 
                       ) 
                     
                   
                   = 
                   
                     max 
                     ( 
                     
                       
                         
                           
                             ξ 
                              
                             
                               ( 
                               
                                 ω 
                                 , 
                                 m 
                               
                               ) 
                             
                           
                           
                             1 
                             + 
                             
                               ξ 
                                
                               
                                 ( 
                                 
                                   ω 
                                   , 
                                   m 
                                 
                                 ) 
                               
                             
                           
                         
                       
                       , 
                       
                         
                           β 
                           P 
                         
                          
                         
                           ( 
                           ω 
                           ) 
                         
                       
                     
                     ) 
                   
                 
               
               
                 
                   ( 
                   18 
                   ) 
                 
               
             
           
         
       
     
         [0100]    The output value by the residual-noise-suppression-gain calculation unit  110  can be expressed as follow. 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         
                           
                             
                               X 
                               P 
                             
                              
                             
                               ( 
                               ω 
                               ) 
                             
                           
                           = 
                             
                            
                           
                             
                               
                                 X 
                                 S 
                               
                                
                               
                                 ( 
                                 ω 
                                 ) 
                               
                             
                              
                             
                               
                                 G 
                                 P 
                               
                                
                               
                                 ( 
                                 ω 
                                 ) 
                               
                             
                           
                         
                       
                     
                     
                       
                         
                           = 
                             
                            
                           
                             
                               
                                 ds 
                                 
                                   
                                       
                                   
                                   1 
                                 
                               
                                
                               
                                 ( 
                                 ω 
                                 ) 
                               
                             
                              
                             
                               
                                 G 
                                 T 
                               
                                
                               
                                 ( 
                                 ω 
                                 ) 
                               
                             
                           
                         
                       
                     
                   
                    
                   
                     
 
                   
                    
                   
                     where 
                     , 
                     
                       
 
                     
                      
                     
                       
                         
                           G 
                           T 
                         
                          
                         
                           ( 
                           ω 
                           ) 
                         
                       
                       = 
                       
                         
                           { 
                           
                             
                               
                                 γ 
                                 S 
                               
                                
                               
                                 ( 
                                 
                                   1 
                                   - 
                                   
                                     
                                       G 
                                       BSA 
                                     
                                      
                                     
                                       ( 
                                       ω 
                                       ) 
                                     
                                   
                                 
                                 ) 
                               
                             
                             + 
                             1 
                           
                           } 
                         
                          
                         
                           
                             G 
                             P 
                           
                            
                           
                             ( 
                             ω 
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   19 
                   ) 
                 
               
             
           
         
       
     
         [0101]    Accordingly, as the gain to be multiplied to the output ds 1 (ω) of the beamformer  30 , the gain value G T (ω) which reduces the musical noises and which also suppresses the residual noises are recalculated. Moreover, in order to prevent an excessive suppression of the target sound, the value of λ d (ω) can be adjusted in accordance with the external VAD information and the value of the control signal from the control unit  160  of the present invention. 
         [0102]    (Gain Multiplication Unit) 
         [0103]    The output G BSA (ω) of the weighting-factor calculation unit  50 , the output G S (ω) of the musical-noise-reduction-gain calculation unit  60 , or the output G T (ω) of the residual-noise-suppression calculation unit  110  is used as an input to a gain multiplication unit  130 . The gain multiplication unit  130  outputs the signal X BSA (ω) based on a multiplication result of the output ds 1 (ω) of the beamformer  30  by the weighting factor G BSA (ω), the musical noise reducing gain G S (ω), or the residual noise suppression G T (ω). That is, as a value of X BSA (ω), for example, a multiplication value of ds 1 (ω) by G BSA (ω) a multiplication value of ds 1 (ω) by G S (ω), or a multiplication value of ds 1 (ω) by G T (ω) can be used. 
         [0104]    In particular, the sound source signal from the target sound source and obtained from the multiplication value of ds 1 (ω) by G T (ω) contains extremely little musical noises and noise components. 
         [0000]        X   BSA (ω)= G   T (ω) ds   1 (ω)  (20)
 
         [0105]    (Time-Waveform Transformation Unit) 
         [0106]    The time-waveform transformation unit  120  transforms the output X BSA (ω) of the gain multiplication unit  130  into a time domain signal. 
         [0107]    (Another Configuration of Sound Source Separation System) 
         [0108]      FIG. 8  is a diagram showing another illustrative configuration of a sound source separation system according to this embodiment. The difference between this configuration and the configuration of the sound source separation system shown in  FIG. 1  is that the noise estimation unit  70  of the sound source separation system in  FIG. 1  is realized over a time domain, but it is realized over a frequency domain according to the sound source separation system shown in  FIG. 8 . The other configurations are consistent with those of the sound source separation system shown in  FIG. 1 . According to this configuration, the spectrum analyze unit  80  becomes unnecessary. 
       Second Embodiment 
       [0109]      FIG. 9  is a diagram showing a basic configuration of a sound source separation system according to a second embodiment of the present invention. The feature of the sound source separation system of this embodiment is to include a control unit  160 . The control unit  160  controls respective internal parameters of the noise estimation unit  70 , the noise equalizer  100 , and the residual-noise-suppression-gain calculation unit  110  based on the weighting factor G BSA (ω) across the entire frequency band. Example internal parameters are a step size of the adaptive filter, a spectrum floor value β of the weighting factor G BSA (ω), and a noise quantity of estimated noises. 
         [0110]    More specifically, the control unit  160  executes following processes. For example, an average value of the weighting factor G BSA (ω) across the entire frequency band is calculated. If such an average value is large, it is possible to make a determination that a sound presence probability is high, so that the control unit  160  compares the calculated average and a predetermined threshold, and controls other blocks based on the comparison result. 
         [0111]    Alternatively, for example, the control unit  160  calculates, from 0 to 1.0, the histogram of the weighting factor G BSA (ω) calculated by the weighting-factor calculation unit  50  for each 0.1. When the value of G BSA (ω) is large, the probability that sound is present is high, and when the value of G BSA (ω) is small, the probability that sound is present is low. Accordingly, a weighting table indicating such a tendency is prepared in advance. Next, the calculated histogram is multiplied by such a weighting table to calculate an average value, the average value is compared with a threshold, and the other blocks are controlled based on the comparison result. 
         [0112]    Moreover, for example, the control unit  160  calculates, from 0 to 1.0, the histogram of the weighting factor G BSA (ω) for each 0.1, counts the number of histograms distributed within a range from 0.7 to 1.0 for example, compares such a number with a threshold, and controls the other blocks based on the comparison result. 
         [0113]    Furthermore, the control unit  160  may receive an output signal from at least either one of the two microphones (microphones  10  and  11 ).  FIG. 10  is a block diagram showing the control unit  160  in this case. The basic idea for the process by the control unit  160  is that an energy comparison unit  167  compares the power spectrum density of the signal X BSA (ω) obtained by multiplying ds 1 (ω) by G BSA (ω) with the power spectrum density of the output X ABM (ω) of the process by the noise estimation unit  165  and the spectrum analyze unit  166 . 
         [0114]    More specifically, when it is presumed that X BSA (ω)′ and X ABM (ω)′ are obtained by obtaining logarithms for respective power spectrum densities of X BSA (ω) and X ABM (ω), and smoothing respective logarithms, the control unit  160  calculates an estimated SNR D(ω) of the target sound as follow. 
         [0000]        D (ω)=max( X   BSA   ′−X   ABM ′,0)  (25)
 
         [0115]    Next, like the above-explained process by the noise estimation unit  70  and the spectrum analyze unit  80 , a stationary (noise) component D N (ω) is detected from D(ω), and D N (ω) is subtracted from D(ω). Accordingly, a non-stationary noise component D S (ω) contained in D(ω) can be detected. 
         [0000]        D   S (ω)= D (ω)− D   N (ω)  (26)
 
         [0116]    Eventually, D S (ω) and a predetermined threshold are compared with each other, and the other control blocks are controlled based on the comparison result. 
       Third Embodiment 
       [0117]    (First Configuration) 
         [0118]      FIG. 11  shows an illustrative basic configuration of a sound source separation system according to a third embodiment of the present invention. 
         [0119]    A sound source separation device  1  of the sound source separation system shown in  FIG. 11  includes a spectrum analyze units  20  and  21 , beamformers  30  and  31 , power calculation units  40  and  41 , a weighting-factor calculation unit  50 , a weighting-factor multiplication unit  310 , and a time-waveform transformation unit  120 . The configuration other than the weighting-factor multiplication unit  310  is consistent with the configurations of the above-explained other embodiments. 
         [0120]    The weighting-factor multiplication unit  310  multiplies a signal ds 1 (ω) obtained by the beamformer  30  by a weighting factor calculated by the weighting-factor calculation unit  50 . 
         [0121]    (Second Configuration) 
         [0122]      FIG. 12  is a diagram showing another illustrative basic configuration of a sound source separation system according to the third embodiment of the present invention. 
         [0123]    A sound source separation device  1  of the sound source separation system shown in  FIG. 12  includes spectrum analyze units  20  and  21 , beamformers  30  and  31 , power calculation units  40  and  41 , a weighting-factor calculation unit  50 , a weighting-factor multiplication unit  310 , a musical-noise reduction unit  320 , a residual-noise suppression unit  330 , a noise estimation unit  70 , a spectrum analysis unit  80 , a power calculation unit  90 , a noise equalizer  100 , and a time-waveform transformation unit  120 . The configuration other than the weighting-factor multiplication unit  310 , the musical-noise reduction unit  320 , and the residual-noise suppression unit  330  is consistent with the configurations of the above-explained other embodiments. 
         [0124]    The musical-noise reduction unit  320  outputs a result of adding an output result by the weighting-factor multiplication unit  310  and a signal obtained from the beamformer  30  at a predetermined ratio. 
         [0125]    The residual-noise suppression unit  330  suppresses residual noises contained in an output result by the musical-noise reduction unit  320  based on the output result by the musical-noise reduction unit  320  and an output result by the noise equalizer  100 . 
         [0126]    Moreover, according to the configuration shown in  FIG. 12 , the noise equalizer  100  calculates noise components contained in the output result by the musical-noise reduction unit  320  based on the output result by the musical-noise reduction unit and the noise components calculated by the noise estimation unit  70 . 
         [0127]    A signal X S (ω) obtained by adding, at a predetermined ratio, a signal X BSA (ω) obtained by multiplying the output ds 1 (ω) of the beamformer  30  by a weighting factor G BSA (ω) and the output ds 1 (ω) of the beamformer  30  may contain non-stationary noises depending on a noise environment. Hence, in order to enable estimation of non-stationary noises, the noise estimation unit  70  and the noise equalizer  100  to be discussed later are introduced. 
         [0128]    According to the above-explained configuration, the sound source separation device  1  of  FIG. 12  separates, from mixed sounds, a sound source signal from the target sound source based on the output result by the residual-noise suppression unit  330 . 
         [0129]    That is, the sound source separation device  1  of  FIG. 12  differs from the sound source separation devices  1  of the first embodiment and the second embodiment that no musical-noise-reduction gain G S (ω) and residual-noise suppression-gain G T (ω) are calculated. According to the configuration shown in  FIG. 12 , also, the same advantage as that of the sound source separation device  1  of the first embodiment can be obtained. 
         [0130]    (Third Configuration) 
         [0131]    Moreover,  FIG. 13  shows the other illustrative basic configuration of a sound source separation system according to the third embodiment of the present invention. A sound source separation device  1  shown in  FIG. 13  includes a control unit  160  in addition to the configuration of the sound source separation device  1  of  FIG. 12 . The control unit  160  has the same function as that of the second embodiment explained above. 
       Fourth Embodiment 
       [0132]      FIG. 14  is a diagram showing a basic configuration of a sound source separation system according to a fourth embodiment of the present invention. The feature of the sound source separation system of this embodiment is to include a directivity control unit  170 , a target sound compensation unit  180 , and an arrival direction estimation unit  190 . 
         [0133]    The directivity control unit  170  performs a delay operation on either one of the microphone outputs subjected to frequency analysis by the spectrum analysis units  20  and  21 , respectively, so that two sound sources R 1  and R 2  to be separated are virtually as symmetrical as possible relative to the separation surface based on a target sound position estimated by the arrival direction estimation unit  190 . That is, the separation surface is virtually rotated, and an optimized value for the rotation angle at this time is calculated based on a frequency band. 
         [0134]    When a beamformer unit  3  performs filtering after the directivity is narrowed down by the directivity control unit  170 , the frequency characteristics of the target sound may be slightly distorted. Moreover, when a delay amount is given to the input signal to the beamformer unit  3 , the output gain becomes small. Hence, the target sound compensation unit  180  corrects the frequency characteristics of the target sound. 
         [0135]    (Directivity Control Unit) 
         [0136]      FIG. 25  shows a condition in which two sound sources R′ 1  (target sound) and R′ 2  ‘(noises) are symmetrical with respect to a separation surface rotated by θτ relative to the original separation surface intersecting a line interconnecting the microphones. As is disclosed in Patent Document 1, when a certain delay amount τ d  is given to a signal obtained by the one microphone, an equivalent condition to the condition shown in  FIG. 25  can be realized. That is, in order to operate a phase difference between the microphones and to adjust the directivity characteristics, in the above-explained formula (1), a phase rotator D(ω) is multiplied. In a following formula, W 1 (ω)=W 1 (ω, θ 1 , θ 2 ), X(ω)=X(ω, θ 1 , θ 2 ). 
         [0000]        ds   1 (ω)= W   1   H (ω) D (ω) X (ω)  (27-1)
 
         [0000]        D (ω)=exp( jωτ   d )  (27-2)
 
         [0137]    The delay amount τ d  can be calculated as follow. 
         [0000]    
       
         
           
             
               
                 
                   
                     τ 
                     d 
                   
                   = 
                   
                     
                       d 
                        
                       
                           
                       
                        
                       sin 
                        
                       
                           
                       
                        
                       
                         θ 
                         τ 
                       
                     
                     c 
                   
                 
               
               
                 
                   ( 
                   28 
                   ) 
                 
               
             
           
         
       
     
         [0138]    Note that d is a distance between the microphones [m] and c is a sound velocity [m/s]. 
         [0139]    When, however, an array process is performed based on phase information, it is necessary to satisfy a spatial sampling theorem expressed by a following formula. 
         [0000]    
       
         
           
             
               
                 
                   d 
                   &lt; 
                   
                     
                       c 
                        
                       
                           
                       
                        
                       π 
                     
                     ω 
                   
                 
               
               
                 
                   ( 
                   29 
                   ) 
                 
               
             
           
         
       
     
         [0140]    A maximum value τ 0  allowable to satisfy this theorem is as follow. 
         [0000]    
       
         
           
             
               
                 
                   
                     d 
                     + 
                     
                       
                         τ 
                         0 
                       
                       · 
                       c 
                     
                   
                   = 
                   
                     
                       
                         
                           c 
                            
                           
                               
                           
                            
                           π 
                         
                         ω 
                       
                       ⇔ 
                       
                         τ 
                         0 
                       
                     
                     = 
                     
                       
                         π 
                         ω 
                       
                       - 
                       
                         d 
                         c 
                       
                     
                   
                 
               
               
                 
                   ( 
                   30 
                   ) 
                 
               
             
           
         
       
     
         [0141]    The larger each frequency ω is, the smaller the allowable delay amount τ 0  becomes. According to the sound source separation device of Patent Document 1, however, since the delay amount given from the formula (27-2) is constant, there is a case in which the formula (29) is not satisfied at a high range of a frequency domain. As a result, as shown in  FIG. 26 , sound of high-range components at an opposite zone deriving from a direction largely different from the desired sound source separation surface is inevitably output. 
         [0142]    Hence, according to the sound source separation device of this embodiment, as shown in  FIG. 15 , an optimized delay amount calculation unit  171  is provided in the directivity control unit  170  to calculate an optimized delay amount satisfying the spatial sampling theorem for each frequency band, not to apply a constant delay to the rotational angle θτ at the time of the virtual rotation of the separation surface, thereby addressing the above-explained technical issue. 
         [0143]    The directivity control unit  170  causes the optimized delay amount calculation unit  171  to determine whether or not the spatial sampling theorem is satisfied for each frequency when the delay amount derived from the formula (28) based on θτ is given. When the spatial sampling theorem is satisfied, the delay amount τ d  corresponding to θτ is applied to the phase rotator  172 , and when no spatial sampling theorem is satisfied, the delay amount τ 0  is applied to the phase rotator  172 . 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         ds 
                         1 
                       
                        
                       
                         ( 
                         ω 
                         ) 
                       
                     
                     = 
                     
                       
                         
                           W 
                           1 
                           H 
                         
                          
                         
                           ( 
                           ω 
                           ) 
                         
                       
                        
                       
                         D 
                          
                         
                           ( 
                           ω 
                           ) 
                         
                       
                        
                       
                         X 
                          
                         
                           ( 
                           ω 
                           ) 
                         
                       
                     
                   
                    
                   
                     
 
                   
                    
                   
                     where 
                     , 
                     
                       
 
                     
                      
                     
                       
                         D 
                          
                         
                           ( 
                           ω 
                           ) 
                         
                       
                       = 
                       
                         { 
                         
                           
                             
                               
                                 diag 
                                  
                                 
                                   ( 
                                   
                                     
                                       exp 
                                        
                                       
                                         [ 
                                         
                                           j 
                                            
                                           
                                               
                                           
                                            
                                           
                                             ωτ 
                                             d 
                                           
                                         
                                         ] 
                                       
                                     
                                     , 
                                     1 
                                   
                                   ) 
                                 
                               
                             
                             
                               
                                 
                                   if 
                                    
                                   
                                       
                                   
                                    
                                   
                                     θ 
                                     τ 
                                   
                                 
                                 &lt; 
                                 
                                   
                                     sin 
                                     
                                       - 
                                       1 
                                     
                                   
                                    
                                   
                                     ( 
                                     
                                       
                                         c 
                                          
                                         
                                             
                                         
                                          
                                         
                                           π 
                                           / 
                                           d 
                                         
                                          
                                         
                                             
                                         
                                          
                                         ω 
                                       
                                       - 
                                       1 
                                     
                                     ) 
                                   
                                 
                               
                             
                           
                           
                             
                               
                                 diag 
                                  
                                 
                                   ( 
                                   
                                     
                                       exp 
                                        
                                       
                                         [ 
                                         
                                           j 
                                            
                                           
                                               
                                           
                                            
                                           
                                             ωτ 
                                             0 
                                           
                                         
                                         ] 
                                       
                                     
                                     , 
                                     1 
                                   
                                   ) 
                                 
                               
                             
                             
                               else 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   31 
                   ) 
                 
               
             
           
         
       
     
         [0144]      FIG. 16  is a diagram showing directivity characteristics of the sound source separation device  1  of this embodiment. As shown in  FIG. 16 , by applying the delay amount of the formula (31), the technical issue such that sound of high-frequency components at the opposite zone arrived from a direction largely different from the desired sound source separation surface is output can be addressed. 
         [0145]    Moreover,  FIG. 17  is a diagram showing another configuration of the directivity control unit  170 . In this case, the delay amount calculated by the optimized delay amount calculation unit  171  based on the formula (31) is not applied to the one microphone input, but respective half delays may be given to both microphone inputs by phase rotators  172  and  173  to realize the equivalent delay operation. That is, a delay amount τ d /2 (or τ 0 /2) is given to a signal obtained through the one microphone, and a delay −τ d /2 (or −τ 0 /2) is given to a signal obtained through another microphone, thereby accomplishing a difference in delay of τ d  (or τ 0 ), not by giving the delay τ d  (or τ 0 ) to the signal obtained through the one microphone. 
         [0146]    (Target Sound Compensation Unit) 
         [0147]    Another technical issue is that when the beamformers  30  and  31  perform respective BSA processes after the directivity is narrowed down by the directivity control unit  170 , the frequency characteristics of the target sound is slightly distorted. Also, through the process of the formula (31), the output gain becomes small. Hence, the target sound compensation unit  180  that corrects the frequency characteristics of the target sound output is provided to perform frequency equalizing. That is, the place of the target sound is substantially fixed, and thus the estimated target sound position is corrected. According to this embodiment, a physical model that models, in a simplified manner, a transfer function which represents a propagation time from any given sound source to each microphone and an attenuation level is utilized. In this example, the transfer function of the microphone  10  is taken as a reference value, and the transfer function of the microphone  11  is expressed as a relative value to the microphone  10 . At this time, a propagation model X m (ω)=[X m1 (ω), X m2 (ω)] of sound reaching to each microphone from a target sound position can be expressed as follow. Note that γ s  is a distance between the microphone  10  and the target sound, and θ S  is a direction of the target sound. 
         [0000]        X   m1 (ω)=1
 
         [0000]        X   m2 (ω)= u   −1 ·exp{− jωτ   m   d ( u− 1)/ c}   (32)
 
         [0000]      where,  u= 1+(2 /r   m )cos θ m +(1 /r   m   2 )
 
         [0148]    By utilizing this physical model, it becomes possible to simulate in advance how a voice uttered from an estimated target sound position is input into each microphone, and the distortion level to the target sound can be calculated in a simplified manner. The weighting factor to the above-explained propagation model is G BSA (ω|X m (ω)), and the inverse number thereof is retained as a equalizer by the target sound correcting unit  180 , thereby enabling the compensation of frequency distortion of the target sound. Hence, the equalizer can be obtained as follow. 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       E 
                       m 
                     
                      
                     
                       ( 
                       ω 
                       ) 
                     
                   
                   = 
                   
                     1 
                     
                       
                         G 
                         BSA 
                       
                        
                       
                         ( 
                         
                           ω 
                            
                           
                             
                               X 
                               m 
                             
                              
                             
                               ( 
                               ω 
                               ) 
                             
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   33 
                   ) 
                 
               
             
           
         
       
     
         [0149]    Accordingly, the weighting factor G BSA (ω) calculated by the weighting-factor calculation unit  50  is corrected to G BSA ′(ω) by the target sound compensation unit  180  and expressed as a following formula. 
         [0000]        G   BSA ′(ω)= E   m (ω) G   BSA (ω)  (34)
 
         [0150]      FIG. 18  shows the directivity characteristics of the sound source separation device  1  having the equalizer of the target sound compensation unit  180  designed in such a way that θ S  is 0 degree, and γ s  is 1.5 [m]. It can be confirmed from  FIG. 18  that an output signal has no frequency distortion with respect to sound arrived from a sound source in the direction of 0 degree. 
         [0151]    The musical-noise-reduction-gain calculation unit  60  takes the corrected weighting factor G BSA ′(ω) as an input. That is, G BSA (ω) in the formula (7), etc., is replaced with G BSA ′(ω). 
         [0152]    Moreover, at least either one of the signals obtained through the microphones  10  and  11  may be input to the control unit  160 . 
         [0153]    (Flow of Process by Sound Source Separation System) 
         [0154]      FIG. 19  is a flowchart showing an example process executed by the sound source separation system. 
         [0155]    The spectrum analysis units  20  and  21  perform frequency analysis on input signal  1  and input signal  2 , respectively, obtained through the microphones  10  and  20  (steps S 101  and S 102 ). At this stage, the arrival direction estimation unit  190  may estimate a position of the target sound, and the directivity control unit  170  may calculate the optimized delay amount based on the estimated positions of the sound sources R 1  and R 2 , and the input signal  1  may be multiplied by a phase rotator in accordance with the optimized delay amount. 
         [0156]    Next, the beamformers  30  and  31  perform filtering on respective signals x 1 (ω) and x 2 (ω) having undergone the frequency analysis in the steps S 101  and S 102  (steps S 103  and S 104 ). The power calculation units  40  and  41  calculate respective powers of the outputs through the filtering (steps S 105  and S 106 ). 
         [0157]    The weighting-factor calculation unit  50  calculates a separation gain value G BSA (ω) based on the calculation results of the steps S 105  and S 106  (step S 107 ). At this stage, the target sound compensation unit  180  may recalculate the weighting factor value G BSA (ω) to correct the frequency characteristics of the target sound. 
         [0158]    Next, the musical-noise-reduction-gain calculation unit  60  calculates a gain value G S (ω) that reduces the musical noises (step S 108 ). Moreover, the control unit  160  calculates respective control signals for controlling the noise estimation unit  70 , the noise equalizer  100 , and the residual-noise-suppression-gain calculation unit  110  based on the weighting factor G BSA (ω) calculated in the step S 107  (step S 109 ). 
         [0159]    Next, the noise estimation unit  70  executes estimation of noises (step S 110 ). The spectrum analysis unit  80  performs frequency analysis on a result X ABM (t) of the noise estimation in the step S 110  (step S 111 ), and the power calculation unit  90  calculates power for each frequency bin (step S 112 ). Moreover, the noise equalizer  100  corrects the power of the estimated noises calculated in the step S 112 . 
         [0160]    Subsequently, the residual-noise-suppression-gain calculation unit  110  calculates a gain G T (ω) for eliminating the noise components with respect to a value obtained by applying the gain value G S (ω) calculated in the step S 108  to an output value ds 1 (ω) of the beamformer  30  processed in the step S 103  (step S 114 ). Calculation of the gain G T (ω) is carried out based on an estimated value λ d (ω) of the noise components having undergone power correction in the step S 112 . 
         [0161]    The gain multiplication unit  130  multiplies the process result by the beamformer  30  in the step S 103  by the gain calculated in the step S 114  (step S 117 ). 
         [0162]    Eventually, the time-waveform transformation unit  120  transforms the multiplication result (the target sound) in the step S 117  into a time domain signal (step S 118 ). 
         [0163]    Moreover, as explained in the third embodiment, noises may be eliminated from the output signal by the beamformer  30  by the musical-noise reduction unit  320  and the residual-noise suppression unit  330  without through the calculation of the gains in the step S 108  and the step S 114 . 
         [0164]    Respective processes shown in the flowchart of  FIG. 19  can be roughly categorized into three processes. That is, such three processes are an output process from the beamformer  30  (steps S 101  to S 103 ), a gain calculation process (steps S 101  to S 108  and step S 114 ), and a noise estimation process (steps S 110  to S 113 ). 
         [0165]    Regarding the gain calculation process and the noise estimation process, after the weighting factor is calculated through the steps S 101  to S 107  of the gain calculation process, the process in the step S 108  is executed, while at the same time, the process in the step S 109  and the noise estimation process (steps S 110  to S 113 ) are executed, and then the gain to be multiplied by the output by the beamformer  30  is set in the step S 114 . 
         [0166]    (Flow of Process by Noise Estimation Unit) 
         [0167]      FIG. 20  is a flowchart showing the detail of the process in the step S 110  shown in  FIG. 19 . First, a pseudo signal H T (t)·x 1 (t) similar to the signal component from the sound source R 1  is calculated (step S 201 ). Next, the subtractor  72  shown in  FIG. 6  subtracts the pseudo signal calculated in the step S 201  from a signal x 2 (t) obtained through the microphone  11 , and thus an error signal x ABM (t) is calculated which is the output by the noise estimation unit  70  (step S 202 ). 
         [0168]    Thereafter, when the control signal from the control unit  160  is larger than the predetermined threshold (step S 203 ), the adaptive filter  71  updates the adaptive filtering coefficient H(t) (step S 204 ). 
         [0169]    (Flow of Process by Noise Equalizer) 
         [0170]      FIG. 21  is a flowchart showing the detail of the process in the step S 113  shown in  FIG. 19 . First, the output ds 1 (ω) by the beamformer  30  is multiplied by the gain G S (ω) output by the musical-noise-reduction-gain calculation unit  60 , and an output X S (ω) is obtained (step S 301 ). 
         [0171]    When the control signal from the control unit  160  is smaller than the predetermined threshold (step S 302 ), the smoothing unit  103  shown in  FIG. 7  executes a time smoothing process on an output pX S (ω) by the power calculation unit  102 . Moreover, the smoothing unit  104  executes a time smoothing process on an output pX ABM (ω) by the power calculation unit  90  (steps S 303 , S 304 ). 
         [0172]    The equalizer updating unit  106  calculates a ratio H EQ (ω) of the process results in the step S 303  and the step S 304 , and the equalizer value is updated to H EQ (ω) (step S 305 ). Eventually, the equalizer adaptation unit  107  calculates the estimated noises λ d (ω) contained in X S (ω) (step S 306 ). 
         [0173]    (Flow of Process by Residual-Noise-Suppression-Gain Calculation Unit  110 ) 
         [0174]      FIG. 22  is a flowchart showing the detail of the process in the step S 114  in  FIG. 19 . When the control signal from the control unit  160  is larger than the predetermined threshold (step S 401 ), a process of reducing the value of λ d (ω) which is the output by the noise equalizer  100  and which is also an estimated value of the noise components to be, for example, 0.75 times (step S 402 ). Next, a posteriori-SNR is calculated (step S 403 ). Moreover, a priori-SNR is also calculated (step S 404 ). Eventually, the residual-noise suppression gain G T (ω) is calculated (step S 405 ). 
       Other Embodiments 
       [0175]    In the calculation of the gain value G BSA (ω) by the weighting-factor calculation unit  50 , the weighting factor may be calculated using a predetermined bias value γ(ω). For example, the predetermined bias value may be added to the denominator of the gain value G BSA (ω), and a new gain value may be calculated. It can be expected that addition of the bias value improves, in particular, the low-frequency SNR when the gain characteristics of the microphones are consistent with each other and a target sound is present near the microphone like the cases of a headset and a handset. 
         [0176]      FIGS. 23 and 24  are diagrams showing a graph for comparing the output value by the beamformer  30  between near-field sound and far-field sound. In  FIGS. 23 and 24 , A 1  to A 3  are graphs showing an output value for near-field sound, and B 1  to B 3  are graphs showing an output value for far-field sound. In  FIG. 23 , a pitch between the microphone  10  and the microphone  11  was 0.03 m, and the distances between the microphone  10  and the sound sources R 1  and R 2  were 0.06 m (meter) and 1.5 m, respectively. Moreover, in  FIG. 24 , a pitch between the microphone  10  and the microphone  11  was 0.01 m and the distances between the microphone  10  and the sound sources R 1  and R 2  were 0.02 m (meter) and 1.5 m, respectively. 
         [0177]    For example, FIG.  23 A 1  is a graph showing a value of an output value ds 1 (ω) (=|X(ω)W 1 (ω)| 2 ) by the beamformer  30  in accordance with near-field sound, and FIG.  23 B 1  is a graph showing a value of ds 1 (ω) in accordance with far-field sound. In this example, the target sound correcting unit  180  was designed in such a way that the near-field sound was the target sound, and in the case of the far-field sound, the target sound correcting unit  180  affected the value of ps 1 (ω) so as to be small at a low frequency. Moreover, when the value of ds 1 (ω) is small (i.e., when the value of ps 1 (ω) is small), the effect of γ(ω) becomes large. That is, since the item of the denominator becomes large relative to the numerator, G BSA (ω) becomes further small. Hence, the low frequency of the far-filed sound is suppressed. 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       G 
                       BSA 
                     
                      
                     
                       ( 
                       ω 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         max 
                          
                         
                           ( 
                           
                             
                               
                                 
                                   ps 
                                   1 
                                 
                                  
                                 
                                   ( 
                                   ω 
                                   ) 
                                 
                               
                               - 
                               
                                 
                                   ps 
                                   2 
                                 
                                  
                                 
                                   ( 
                                   ω 
                                   ) 
                                 
                               
                             
                             , 
                             0 
                           
                           ) 
                         
                       
                       
                         
                           
                             ps 
                             1 
                           
                            
                           
                             ( 
                             ω 
                             ) 
                           
                         
                         + 
                         
                           γ 
                            
                           
                             ( 
                             ω 
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   35 
                   ) 
                 
               
             
           
         
       
     
         [0178]    Moreover, according to the configuration shown in  FIG. 7 , G BSA (ω) obtained from the formula (35) is applied to the output value ds 1 (ω) by the beamformer  30 , and the multiplication result X BSA (ω) of ds 1 (ω) by G BSA (ω) is calculated as follow. In the following formula, as an example case, the sound source separation device  1  employs the configuration shown in  FIG. 7 . 
         [0000]        X   BSA (ω)= G   BSA (ω) ds   1 (ω)  (36)
 
         [0179]    As explained above, in  FIGS. 23 and 24 , A 1  and B 1  are graphs showing the output ds 1 (ω) by the beamformer  30 . Moreover, A 2  and B 2  in respective figures are graphs showing the output X BSA (ω) when no γ(ω) is inserted in the denominator of the formula (35). Furthermore, A 3  and B 3  of respective figures are graphs showing the output X BSA (ω) when γ(ω) is inserted in the denominator of the formula (35). It becomes clear from respective figures that the low frequency of the far-field sound is suppressed. That is, an effect is expectable for road noises, etc., present mainly in the low frequency. 
         [0180]    In the above explanation, the beamformer  30  configures a first beamformer processing unit. Moreover, the beamformer  31  configures a second beamformer processing unit. Furthermore, the gain multiplication unit  130  configures a sound source separation unit. 
       INDUSTRIAL APPLICABILITY 
       [0181]    The present invention is applicable to all industrial fields that need precise separation of a sound source, such as a voice recognition device, a car navigation, a sound collector, a recording device, and a control for a device through a voice command. 
       REFERENCE SIGNS LIST 
       [0000]    
       
         
           
               1  Sound source separation device 
               3  Beamformer unit 
               10 ,  11  Microphone 
               20 ,  21  Spectrum analysis unit 
               30 ,  31  Beamformer 
               40 ,  41  Power calculation unit 
               50  Weighting-factor calculation unit 
               60  Musical-noise-reduction-gain calculation unit 
               70  Noise estimation unit 
               71  Adaptive filter 
               72  Subtractor 
               73  Delay device 
               74  Threshold comparison unit 
               80  Spectrum analysis unit 
               90  Power calculation unit 
               100  Noise equalizer 
               101  Multiplier 
               102  Power calculation unit 
               103 ,  104  Smoothing unit 
               105  Threshold comparison unit 
               106  Equalizer updating unit 
               107  Equalizer adaptation unit 
               110  Residual-noise-suppression-gain calculation unit 
               120  Time-waveform transformation unit 
               130  Gain multiplication unit 
               160  Control Unit 
               161 A,  161 B Spectrum analysis unit 
               162 A,  162 B Beamformer 
               163 A,  163 B Power calculation unit 
               164  Weighting-factor calculation unit 
               165  Noise estimation unit 
               166  Spectrum analysis unit 
               167  Energy comparison unit 
               170  Directivity control unit 
               171  Optimized delay amount calculation unit 
               172 ,  173  Phase rotator 
               180  Target sound correction unit 
               190  Arrival direction estimation unit 
               310  Weighting-factor multiplication unit 
               320  Musical-noise reduction unit 
               330  Residual-noise suppression unit