Patent Publication Number: US-7711558-B2

Title: Apparatus and method for detecting voice activity period

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is based on and claims priority from Korean Patent Application No. 10-2005-0089526, filed on Sep. 26, 2005, the disclosure of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to voice activity detection, and more particularly to an apparatus and method for detecting a speech signal period from an input signal by using spectral subtraction and a probability distribution model. 
   2. Description of Related Art 
   With the development of technology, various devices have been developed that can more conveniently maintain peoples&#39; lifestyles. In particular, devices have been provided that can recognize speech and properly react to it. This capability is known as speech recognition. 
   The principal technologies of such speech recognition include a technology that detects a period where a speech signal is present in an input signal, and a technology that captures the content included in the detected speech signal. 
   Voice detection technology is required in speech recognition and speech compression. The core of this technology is to distinguish the speech and noise of an input signal. 
   A representative example of this technology includes the “Extended Advanced Front-end Feature Extraction Algorithm” (hereinafter, referred to as “first conventional art”) which was selected by the European Telecommunication Standard Institute (ETSI) in November of 2003. According to this algorithm, a voice activity period is detected based on energy information in a speech frequency band by using a temporal change of a feature parameter with respect to a speech signal in which a noise is removed. However, when the noise level is high, performance may be deteriorated. 
   Also, Korean Patent No. 10-304666 (hereinafter, referred to as “second conventional art”) discloses a method for detecting a voice activity period by estimating in real-time each component of a noise signal and a speech signal from a speech signal having noise using statistical modeling such as the complex Gaussian distribution. However, even in this case, when the magnitude of a noise signal becomes greater than the magnitude of a speech signal, a voice activity period may not be detected. 
   According to the above-described conventional art, a signal-to-noise ratio (hereinafter, referred to as “SNR”) decreases, that is, the magnitude of noise increases, and thus it may not be easy to distinguish a speech period from a noise period, as shown in  FIGS. 1A to 1D . 
     FIGS. 1A to 1D  are histograms illustrating a distribution of a speech signal  110  having noise and a noise signal  120  according to a change in an SNR. Referring to  FIGS. 1A to 1D , an x-X-axis represents the magnitude of band energy in a frequency band between 1 kHz and 1.03 kHz, and a y-axis represents a probability with respect thereto. 
   Also,  FIG. 1A  illustrates a histogram when an SNR is 20 dB,  FIG. 1B  illustrates a histogram when an SNR is 10 dB,  FIG. 1C  illustrates a histogram when an SNR is 5 dB, and  FIG. 1D  illustrates a histogram when an SNR is 0 dB. 
   Referring to  FIGS. 1A to 1D , as the SNR value decreases, the speech signal  110  having noise is more concealed by the noise signal  120 . Accordingly, the speech signal  110  having noise may not be distinguished from the noise signal  120 . 
   Specifically, according to the conventional methods, a speech period and a noise period may not be easily distinguished from each other in an input signal having a low SNR value. 
   BRIEF SUMMARY 
   An aspect of the present invention provides an apparatus and method for detecting a voice activity period that can reduce an error of distribution estimation by estimating the distribution of a speech period and a noise period even in a low SNR region and by using a statistical modeling method with respect to an estimated speech spectrum. 
   According to an aspect of the present invention, there is provided an apparatus for detecting a voice activity period, which includes a domain conversion module converting an input signal into a frequency domain signal in the unit of a frame obtained by dividing the input signal at predetermined intervals, a subtracted-spectrum-generation module generating a spectral subtraction signal which is obtained by subtracting a predetermined noise spectrum from the converted frequency domain signal, a modeling module applying the spectral subtraction signal to a predetermined probability distribution model, and a speech-detection module determining whether a speech signal is present in a current frame through a probability distribution calculated by the modeling module. 
   According to another aspect of the present invention, there is provided a method of detecting a voice activity period, which includes converting an input signal into a frequency domain signal in the unit of a frame obtained by dividing the input signal at predetermined intervals, generating a spectral subtraction signal which is obtained by subtracting a predetermined noise spectrum from the converted frequency domain signal, applying the spectral subtraction signal to a predetermined probability distribution model, and determining whether a speech signal is present in a current frame through a probability distribution according to an application of the probability distribution model. 
   According to another aspect of the present invention, there is provided a computer-readable storage medium encoded with processing instructions for causing a processor to execute the aforementioned method. 
   Additional and/or other aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and/or other aspects and advantages of the present invention will become apparent and more readily appreciated from the following detailed description, taken in conjunction with the accompanying drawings of which: 
       FIGS. 1A to 1D  are histograms illustrating the distribution of a speech signal having noise and a noise signal according to a change in an SNR; 
       FIG. 2  is a block diagram illustrating the construction of an apparatus for detecting a voice activity period according to an embodiment of the present invention; 
       FIG. 3  is a flowchart illustrating a method of detecting a voice activity period according to an embodiment of the present invention; 
       FIGS. 4A and 4B  are histograms illustrating a subtraction effect of a noise spectrum according to an embodiment of the present invention; 
       FIG. 5  is a graph illustrating Rayleigh-Laplace distribution according to an embodiment of the present invention; and 
       FIG. 6  is a graph illustrating the results of performance evaluation according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF EMBODIMENTS 
   Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. 
   Embodiments of the present invention are described hereinafter with reference to flowchart illustrations of user interfaces, methods, and computer program products according to embodiments of the invention. It should be understood that each block of the flowchart illustrations, and combinations of blocks in the flowchart illustrations, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart block or blocks. 
   These computer program instructions may also be stored in a computer-usable or computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-usable or computer-readable memory produce an article of manufacture including instruction means that implement the function specified in the flowchart block or blocks. 
   The computer program instructions may also be loaded into a computer or other programmable data processing apparatus to cause a series of operations to be performed in the computer or other programmable apparatus to produce a computer implemented process such that the instructions that execute in the computer or other programmable apparatus provide operations for implementing the functions specified in the flowchart block or blocks. 
   Also, each block of the flowchart illustrations may represent a module, segment, or portion of code, which includes one or more executable instructions for implementing the specified logical function(s). It should also be noted that in some alternative implementations, the functions noted in the blocks may occur in an order that differs from that illustrated and/or described. For example, two blocks shown in succession may be executed substantially concurrently or the blocks may sometimes be executed in reverse order depending upon the functionality involved. 
   In the following embodiment of the present invention, the term “module”, as used herein, means, but is not limited to, a software or hardware component, such as a Field Programmable Gate Array (FPGA) or an Application Specific Integrated Circuit (ASIC), which performs certain tasks. A module may advantageously be configured to reside on the addressable storage medium and configured to execute on one or more processors. Thus, a module may include, by way of example, components, such as software components, object-oriented software components, class components and task components, processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays, and variables. The functionality provided for in the components and modules may be combined into fewer components and modules or further separated into additional components and modules. In addition, the components and modules may be implemented so as to execute one or more CPUs in a device. 
     FIG. 2  is a block diagram illustrating the construction of an apparatus for detecting a voice activity period according to an embodiment of the present invention. 
   Referring to  FIG. 2 , an apparatus  200  for detecting a voice activity period according to the embodiment of the present invention includes a signal input module  210 , a domain conversion module  220 , a subtracted-spectrum-generation module  230 , a modeling module  240  and a speech-detection module  250 . 
   The signal input module  210  receives an input signal using a device such as, by way of a non-limiting example, a microphone. The domain conversion module  220  converts an input signal into a frequency domain signal. Specifically, the domain conversion module  220  converts a time domain input signal into a frequency domain signal. 
   Advantageously, the domain conversion module  220  may perform a domain conversion operation of the input signal in the unit of a frame which is obtained by dividing the input signal at predetermined time intervals. In this case, one frame corresponds to one signal period, and the domain conversion operation of the (n+1)-th frame is performed after a speech detection operation of the n-th frame is completed. 
   The subtracted-spectrum-generation module  230  generates a signal (hereinafter, referred to as “spectral subtraction signal”) obtained by subtracting a predetermined noise spectrum of a previous frame from an input frequency spectrum of an input signal. 
   The noise spectrum may be calculated by using speech absence probability information received from the modeling module  240 . 
   The modeling module  240  sets a predetermined probability distribution model and applies a spectral subtraction signal received from the subtracted-spectrum-generation module  230  to the set probability distribution model. In this case, the speech-detection module  250  determines whether a speech signal is present in a current frame based on the calculated probability distribution by the modeling module  240 . 
     FIG. 3  is a flowchart illustrating a method of detecting a voice activity period according to an embodiment of the present invention. For ease of explanation only, this method is described with reference to the apparatus of  FIG. 2 . However, it is to be understood that the method may be executed by apparatuses of both similar and dissimilar configurations to that of  FIG. 2 . 
   A signal is input via the signal input module  210  S 310 . A frame of the input signal is generated by the domain conversion module  220  S 320 . In this case, the frame of the input signal may be transmitted to the domain conversion module  220  after being generated by the signal input module  210 . 
   The generated frame undergoes a Fast Fourier Transform (FFT) by means of the domain conversion module  220 , and is expressed as a frequency domain signal S 330 . Specifically, a time domain input signal is converted into a frequency domain input signal. 
   If it is assumed that an absolute value of a frequency spectrum generated by the FFT is Y, the subtracted-spectrum-generation module  230  subtracts a noise spectrum N e  from Y S 350 , wherein U represents the subtracted result. 
   The noise spectrum N e  represents an estimate of a noise spectrum with respect to a previous frame. Accordingly, supposing that a frame index is t, U can be expressed as:
 
 U ( t )= Y ( t )− N   e ( t− 1)  (1)
 
In this case, N e (t) may be modeled by:
 
 N   e ( t )=η P   0   Y ( t )+(1 ηP   0 ) N   e ( t− 1)  (2)
 
In Equation 2, η represents a noise updating rate and has a value between 0 and 1. Also, P 0  represents a probability that a speech signal is absent from a t-th frame and is a value calculated by the modeling module  240 .
 
   The subtracted-spectrum-generation module  230  updates a noise spectrum using Y and P 0  received from the modeling module  240  S 340 . N e (t), which is the updated noise spectrum according to the Equation 1, is used as a noise spectrum to be subtracted from a next frame. 
   Results of subtracting a noise spectrum as described above are shown in  FIGS. 4A and 4B . 
     FIGS. 4A and 4B  are histograms illustrating a subtraction effect of a noise spectrum according to an embodiment of the present invention. Referring to  FIGS. 4A and 4B , the x-axis indicates the magnitude of band energy in a frequency band between 1 kHz and 1.03 kHz, and the y-axis indicates a probability with respect thereto. 
   In  FIG. 4A , an SNR of an input signal is 5 dB. When a speech signal  410  having noise and a noise signal  420  are subtracted by the updated noise spectrum N e , an intersection point of a subtracted speech signal  412  and noise signal  422  is inclined towards a point where a band energy level (x-axis) is 0. Accordingly, to distinguish the speech signal  412  and the noise signal  422  from the input signal is easier than before subtracting the noise spectrum N e . 
   In  FIG. 4B , an SNR of an input signal is 0 dB. Even in this case, when a speech signal  430  containing noise and a noise signal  440  are subtracted by the updated noise spectrum N e , an intersection point of a subtracted speech signal  412  and a noise signal  422  is inclined towards a point where a band energy level (x-axis) is 0. Accordingly, distinguishing the speech signal  412  and the noise signal  422  from the input signal is easier than before subtracting the noise spectrum N e . 
   Specifically, even when an SNR of an input signal is 0 dB, an overlapping area is decreased in a distribution of a speech signal and a noise signal. Also, the speech signal and the noise signal can easily be distinguished from the input signal. 
   The modeling module  240  receives a spectrum U subtracted from the subtracted-spectrum-generation module  230  and calculates a speech presence probability in U S 360 . 
   In the present embodiment, a statistical modeling method is used to calculate a speech presence probability. 
   As shown in  FIGS. 4A and 4B , as a result of subtracting a noise spectrum from an input signal, there is a tendency that an intersection point of a speech signal and a noise signal is inclined towards a point where a band energy level (X-axis) is 0. Accordingly, a probability error may be reduced by applying a statistical model whose peak is close to 0 of a band energy level and whose histogram has a long tail. 
   As such a statistical model, the present embodiment utilizes a Rayleigh-Laplace distribution model. 
   The Rayleigh-Laplace distribution model applies a Laplace distribution to a Rayleigh distribution model. The detailed process will be described. 
   First of all, the Rayleigh distribution is defined as a probability density function of a complex random variable z. At this time, the complex random variable z can be expressed as:
 
 z=r (cos θ+ j  sin θ)= x+jy  
 
 x=r  cos θ,  y=r  sin θ  (3)
 
In Equation 3, r represents the magnitude or envelope, and θ represents a phase.
 
   When two random processes x and y depend on Gaussian distribution having the identical variance and 0 as average, probability density functions P(x) and P(y) with respect to x and y respectively may be given by Equation 4 below, wherein σ 2  indicates variance. 
               P   ⁡     (   x   )       =       1       2   ⁢   π   ⁢           ⁢     σ   xy   2           ⁢     exp   ⁡     (     -       x   2       2   ⁢           ⁢     σ   xy   2           )           ,       P   ⁡     (   y   )       =       1       2   ⁢   π   ⁢           ⁢     σ   xy   2           ⁢     exp   ⁡     (     -       y   2       2   ⁢           ⁢     σ   xy   2           )                 
In this case, when it is assumed that x and y are statistically independent, a probability density function P(x,y) taking x and y as variables can be expressed by Equation 5:
 
             P   ⁡     (     x   ,   y     )       =         P   ⁡     (   x   )       ⁢     P   ⁡     (   y   )         =       1     2   ⁢   π   ⁢           ⁢     σ   xy   2         ⁢     exp   ⁡     (     -         x   2     +     y   2         2   ⁢     σ   xy   2           )                 
When differential areas dxdy are converted into dxdy=r dr dθ, a joint probability density function for r and θ can be expressed by Equation 6:
 
             P   ⁡     (     r   ,   θ     )       =       r   ·     P   ⁡     (     x   ,   y     )         =       r     2   ⁢   π   ⁢           ⁢     σ   xy   2         ⁢     exp   ⁡     (     -       r   2       2   ⁢     σ   xy   2           )                 
Also, when integrating P(r,θ) with respect to θ, a probability density function P(r) of r can be expressed by Equation 7:
 
                   p   ⁡     (   r   )       =         ∫   0     2   ⁢   π       ⁢       P   ⁡     (     r   ,   θ     )       ⁢     ⅆ   θ     ⁢           ⁢   for   ⁢           ⁢   r       ≥   0                 =       ∫   0     2   ⁢   π       ⁢       r     2   ⁢           ⁢   π   ⁢           ⁢     σ   xy   2         ⁢     exp   ⁡     (     -       r   2       2   ⁢           ⁢     σ   xy   2           )       ⁢     ⅆ   θ                     =       r     σ   xy   2       ⁢     exp   ⁡     (     -       r   2       2   ⁢     σ   xy   2           )                     
In this case, since σ r   2  with respect to r may be expressed by Equation 8:
 σ r   2   =E[r   2   ]=E[x   2   +y   2   ]=E[x   2   ]+E[y   2 ]=2σ xy   2    
P(r) can be expressed by Equation 9:
 
   
     
       
         
           
             P 
             ⁡ 
             
               ( 
               r 
               ) 
             
           
           = 
           
             
               
                 2 
                 ⁢ 
                 r 
               
               
                 σ 
                 r 
                 2 
               
             
             ⁢ 
             
               exp 
               ⁡ 
               
                 ( 
                 
                   - 
                   
                     
                       r 
                       2 
                     
                     
                       σ 
                       r 
                       2 
                     
                   
                 
                 ) 
               
             
           
         
       
     
   
   In the same manner as the Rayleigh distribution, the Rayleigh-Laplace distribution according to the present embodiment is defined as a probability density function of a complex random variable z like Equation 3. 
   However, contrary to the Rayleigh distribution, in the case of the Rayleigh-Laplace distribution, when two random processes x and y do not depend on Gaussian distribution having the identical variance and 0 as average, but depend on Laplacian distribution known in the art, probability density functions P(x) and P(y) with respect to x and y can be expressed by Equation 10: 
               P   ⁡     (   x   )       =       1       2   ⁢     σ   xy   2           ⁢     exp   ⁡     (       -     2       ⁢          x          σ   xy         )           ,       P   ⁡     (   y   )       =       1       2   ⁢           ⁢     σ   xy   2           ⁢     exp   ⁡     (       -     2       ⁢          y          σ   xy         )                 
When it is assumed that x and y are statistically independent, a probability density function P(x,y) taking x and y as variables can be expressed as Equation 11:
 
             P   ⁡     (     x   ,   y     )       =         P   ⁡     (   x   )       ⁢     P   ⁡     (   y   )         =       1     2   ⁢           ⁢     σ   xy   2         ⁢     exp   ⁡     (       -     2       ⁢            x        +        y            σ   xy         )                 
In this case, when differential areas dxdy are converted into dxdy=r dr dθ and it is supposed that |x|+|y|=r(|sin θ|+|cos θ|)≅r, a joint probability density function of r and θ can be expressed by Equation 12:
 
             P   ⁡     (     r   ,   θ     )       =       r   ·     P   ⁡     (     x   ,   y     )         =       r     2   ⁢           ⁢     σ   xy   2         ⁢     exp   ⁡     (       -     2       ⁢     r     σ   xy         )                 
Also, when integrating P(r,θ) with respect to θ, a probability density function P(r) of r can be expressed as Equation 13:
 
                   P   ⁡     (   r   )       =         ∫   0     2   ⁢   π       ⁢       P   ⁡     (     r   ,   θ     )       ⁢     ⅆ   θ     ⁢           ⁢   for   ⁢           ⁢   r       ≥   0                 =       ∫   0     2   ⁢   π       ⁢       r     2   ⁢           ⁢     σ   xy   2         ⁢     exp   ⁡     (       -     2       ⁢     r     σ   xy         )       ⁢     ⅆ   θ                     =         π   ⁢           ⁢   r       σ   xy   2       ⁢     exp   ⁡     (       -     2       ⁢     r     σ   xy         )                     
In this equation, since σ r   2  of r can be expressed by Equation 14:
 σ r   2   =E└r   2   ┘=E└x   2   +y   2   ┘=E└x   2   ┘+E└y   2 ┘=2σ xy   2    
P(r) can be expressed by Equation 15:
 
             P   ⁡     (   r   )       =         2   ⁢   π   ⁢           ⁢   r       σ   r   2       ⁢     exp   ⁡     (     -       2   ⁢   r       σ   r         )               
Accordingly, when a probability that a speech signal may be present in a current frame according to the embodiment of the present invention is P(Y k (t)|H 1 ), P(Y k (t)|H 1 ) can be modeled by Equation 16:
 
               P   ⁡     (         Y   k     ⁡     (   t   )       |     H   1       )       ≅     P   ⁡     (         U   k     ⁡     (   t   )       |     H   1       )         =         2   ⁢   π   ⁢            U   k     ⁡     (   t   )                  λ     s   ,   k       ⁡     (   t   )         ⁢     exp   ⁡     [     -       2   ⁢            U   k     ⁡     (   t   )                  λ     s   ,   k       ⁢     (   t   )           ]               
In Equation 16, λ s,k (t) is a variance estimate in a k-th frequency bin of a t-th frame. Such a variance estimate may be updated for each frame.
 
   Meanwhile, a probability that a speech signal is absent from a k-th frame may be obtained by utilizing the aforementioned Rayleigh distribution model. In this case, the Rayleigh distribution model has an equivalent characteristic to a statistical model such as a complex Gaussian distribution. 
   When the probability that a speech signal is absent from the k-th frame is P(Y k (t)|H 0 ), P(Y k (t)|H 0 ) can be modeled by Equation 17: 
   
     
       
         
           
             
               P 
               ⁡ 
               
                 ( 
                 
                   
                     
                       Y 
                       k 
                     
                     ⁡ 
                     
                       ( 
                       t 
                       ) 
                     
                   
                   | 
                   
                     H 
                     0 
                   
                 
                 ) 
               
             
             ≅ 
             
               P 
               ⁡ 
               
                 ( 
                 
                   
                     
                       U 
                       k 
                     
                     ⁡ 
                     
                       ( 
                       t 
                       ) 
                     
                   
                   | 
                   
                     H 
                     0 
                   
                 
                 ) 
               
             
           
           = 
           
             
               
                 2 
                 ⁢ 
                 
                    
                   
                     
                       U 
                       k 
                     
                     ⁡ 
                     
                       ( 
                       t 
                       ) 
                     
                   
                    
                 
               
               
                 
                   λ 
                   
                     n 
                     , 
                     k 
                   
                 
                 ⁡ 
                 
                   ( 
                   t 
                   ) 
                 
               
             
             ⁢ 
             
               exp 
               ⁡ 
               
                 [ 
                 
                   - 
                   
                     
                       
                          
                         
                           
                             U 
                             k 
                           
                           ⁡ 
                           
                             ( 
                             t 
                             ) 
                           
                         
                          
                       
                       2 
                     
                     
                       
                         λ 
                         
                           n 
                           , 
                           k 
                         
                       
                       ⁢ 
                       
                         ( 
                         t 
                         ) 
                       
                     
                   
                 
                 ] 
               
             
           
         
       
     
   
   In Equation 17, λ n,k (t) is a variance estimate in the k-th frequency bin of t-th frame. Such a variance estimate may be updated for each frame. 
   For convenience of description, P(Yk(t)|H1)=P 1  and P(Yk(t)|H0)=P 0 . 
     FIG. 5  illustrates a probability distribution curve of the Rayleigh-Laplace distribution model. Referring to  FIG. 5 , a band energy level is more inclined towards 0 than that of the Rayleigh distribution model. It is apparent from a comparison of Equation 9 and Equation 15. 
   Meanwhile, the modeling module  240  transmits the speech absence probability P 0  in a current frame to the subtracted-spectrum-generation module  230  to update a noise spectrum. 
   Also, the modeling module  240  generates an index value which indicates whether a speech signal is present in the current frame, using P 0  and P 1 . 
   For example, when an index value as to whether the speech signal is present in the current frame is A, A can be expressed by Equation 18: 
   
     
       
         
           A 
           = 
           
             
               P 
               1 
             
             
               
                 P 
                 0 
               
               + 
               
                 P 
                 1 
               
             
           
         
       
     
   
   The speech-detection module  250  compares the index value generated by the modeling module  240  with a predetermined reference value and determines that a speech signal is present in the current frame when the index value is above the reference value S 370 . 
     FIG. 6  is a graph illustrating the results of performance evaluation according to an embodiment of the present invention. 
   For experimental materials according to the embodiment, each of 8 males and 8 females uttered 100 words, e.g., persons&#39; names, place names, firm names, etc. Specifically, 16 persons uttered 1600 words. Also, a vehicle noise was utilized as noise. In this instance, the utilized vehicle noise had been recorded in a vehicle which was driving on the highway at 100±10 km/h. 
   Also, for the experiments, the recorded noise was added to a speech signal having no noise (SNR=0 dB). A speech presence region was detected from the speech signal having the recorded noise and also compared with manually written end point information. 
   Meanwhile, the error of speech presence probability (hereinafter, referred to as “ESPP”) and the error of voice activity detection (hereinafter, referred to as “EVAD”) are used as measurement indexes. 
   The ESPP represents the difference between probability induced from a manually written voice activity and detected speech presence probability. The EVAD represents the difference between manually written voice activity and detected voice activity, as ms. 
   In a graph shown in  FIG. 6 , a reference number  610  represents a voice activity period which was written by a human being. Specifically, the human being manually indicates a start point and an end point of a speech signal after listening to a word uttered by another human being. 
   In comparison with the reference number  610 , a reference number  620  represents a voice activity period detected from the speech detection probability according to an embodiment of the present invention and a reference number  630  represents a speech presence probability. 
   As shown in  FIG. 6 , it can be seen that the manually written voice activity period is almost identical to the voice activity period according to the embodiment of the present embodiment. 
   Also, Table 1 shows performance of ESPP according to the present embodiment in comparison with the first prior art and the second prior art as described above. Referring to Table, Y is an input signal that indicates a speech signal having noise. Specifically, Y=S (speech)+N (noise). U is an estimate of a speech signal which is obtained by an appropriate noise prevention algorithm. Specifically, U=Y−N e , wherein N e  represents a noise estimate. 
   
     
       
         
             
           
             
               TABLE 1 
             
           
          
             
                 
             
             
               Estimates of the Speech Signal for ESPP Models 
             
          
         
         
             
             
             
             
          
             
                 
               ESPP Model 
               Y 
               U 
             
             
                 
                 
             
             
                 
               First Conventional Art 
               0.47 
               0.47 
             
             
                 
               Second Conventional Art 
               0.35 
               0.34 
             
             
                 
               Embodiment of Present 
               0.35 
               0.28 
             
             
                 
               Invention 
             
             
                 
                 
             
          
         
       
     
   
   Also, Table 2 and Table 3 show performance of EVAD according to the present invention in comparison with the first prior art and the second prior art. 
   
     
       
         
             
           
             
               TABLE 2 
             
           
          
             
                 
             
             
               Estimates of the Start of Speech Signal for EVAD Models 
             
          
         
         
             
             
             
             
          
             
                 
               EVAD Model 
               Y (ms) 
               U (ms) 
             
             
                 
                 
             
             
                 
               First Conventional Art 
               134 
               134 
             
             
                 
               Second Conventional Art 
               170 
               150 
             
             
                 
               Embodiment of Present 
               144 
               103 
             
             
                 
               Invention 
             
             
                 
                 
             
          
         
       
     
   
   
     
       
         
             
           
             
               TABLE 3 
             
           
          
             
                 
             
             
               Estimates of End Point of Speech Signal for EVAD Models 
             
          
         
         
             
             
             
             
          
             
                 
               EVAD Model 
               Y (ms) 
               U (ms) 
             
             
                 
                 
             
             
                 
               First Conventional Art 
               291 
               291 
             
             
                 
               Second Conventional Art 
               214 
               193 
             
             
                 
               Embodiment of Present 
               196 
               131 
             
             
                 
               Invention 
             
             
                 
                 
             
          
         
       
     
   
   As shown in Tables 1 to 3, it can be seen that at least one embodiment of the present invention is highly effective in voice detection in comparison with the conventional art described above. 
   According to the above-described embodiments of the present invention, it is possible to provide more improved performance in detecting speech of an input signal 
   Although a few embodiments of the present invention have been shown and described, the present invention is not limited to the described embodiments. Instead, it would be appreciated by those skilled in the art that changes may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.