Abstract:
According to an aspect of an embodiment, a method for interpolating a partial loss of an audio signal including a sound signal component and a background noise component in transmission thereof, the method comprising the steps of: calculating frequency characteristic of the background noise in the audio signal; extracting the sound signal component from the audio signal; generating pseudo noise by applying the frequency characteristic of the background noise included in the audio signal to white noise; and generating an interpolation signal by combining the pseudo noise with the extracted sound signal component included in the audio signal to supersede the partial loss of the audio signal.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an interpolation method performed in the transmission of sound in a packet-switching network. 
         [0003]    2. Description of the Related Art 
         [0004]    In the transmission of audit signals via VoIP (Voice over Internet Protocol), packet loss often occurs. The occurrence of the packet loss causes the intermittence of sound, and thus substantially deteriorates the sound quality. To prevent such deterioration of the sound quality, a concealment process has been performed which conceals the loss of an audio signal by performing interpolation for the lost packet. Specifically, the interpolation process for the lost packet is based on ITU-T (International Telecommunication Union Telecommunication Standardization Sector) Recommendation G.711 Appendix 1. The interpolation process based on G.711 Appendix 1 is a process of performing interpolation for the packet loss by calculating the period of a signal immediately preceding the lost packet and repeating the signal with the calculated period while gradually reducing the amplitude of the signal. 
         [0005]    In conventional interpolation processes for the packet loss, such as the one based on G.711 Appendix 1, however, there is an issue of abnormal sound occurring due to an unnatural period generated when the signal immediately preceding the packet loss is a signal having a small periodicity, such as the signal of a consonant, background noise, and so forth. An example of the conventional interpolation processes is disclosed in the publication of International Patent Application Publication No. 2004-068098. 
       SUMMARY 
       [0006]    According to an aspect of an embodiment, a method for interpolating a partial loss of an audio signal including a sound signal component and a background noise component in transmission thereof, the method comprising the steps of: calculating frequency characteristic of the background noise in the audio signal; extracting the sound signal component from the audio signal; generating pseudo noise by applying the frequency characteristic of the background noise included in the audio signal to white noise; and generating an interpolation signal by combining the pseudo noise with the extracted sound signal component included in the audio signal to supersede the partial loss of the audio signal. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a configuration diagram of an information processing device according to one of embodiments of the present invention; 
           [0008]      FIG. 2  is a configuration diagram of an information processing device according to another one of the present embodiments; 
           [0009]      FIG. 3  is a configuration diagram of an information processing device according to another one of the present embodiments; 
           [0010]      FIG. 4  is a configuration diagram of an information processing device according to another one of the present embodiments; 
           [0011]      FIG. 5  is a configuration diagram of an information processing device according to another one of the present embodiments; 
           [0012]      FIG. 6  is a configuration diagram of an information processing device according to another one of the present embodiments; 
           [0013]      FIG. 7  is a configuration diagram of an information processing device according to another one of the present embodiments; 
           [0014]      FIG. 8  is a flowchart of an interpolation process performed by the information processing devices according to the present embodiments; 
           [0015]      FIG. 9  is a flowchart illustrating a processing procedure for calculating the frequency characteristic of background noise performed by analysis unit according to the present embodiments; 
           [0016]      FIG. 10  is a flowchart of a procedure for calculating a sound component performed by the analysis unit according to one of the present embodiments; 
           [0017]      FIG. 11  is a flowchart of a procedure for calculating the envelope of sound and the sound source of the sound performed by the analysis unit according to another one of the present embodiments; 
           [0018]      FIG. 12  is a flowchart of a procedure for calculating the envelope pattern of the sound performed by the analysis unit according to another one of the present embodiments; 
           [0019]      FIG. 13  is a flowchart of a procedure for generating pseudo sound performed by pseudo sound generation unit according to one of the present embodiments; 
           [0020]      FIG. 14  is a schematic diagram illustrating a connection relationship between repeating signal segments according to one of the present embodiments; 
           [0021]      FIG. 15  is a flowchart of a procedure for generating the pseudo sound performed by pseudo sound generation unit according to another one of the present embodiments; 
           [0022]      FIG. 16  is a flowchart of a procedure for generating the pseudo sound performed by pseudo sound generation unit according to another one of the present embodiments; 
           [0023]      FIG. 17  is a flowchart illustrating a procedure for generating pseudo noise performed by pseudo noise generation unit according to one of the present embodiments; 
           [0024]      FIG. 18  is a flowchart of a procedure for generating the pseudo noise performed by pseudo noise generation unit according to another one of the present embodiments; 
           [0025]      FIG. 19  is a flowchart of a procedure for generating an output signal performed by output signal generation unit according to the present embodiments; 
           [0026]      FIG. 20  is a flowchart illustrating a first procedure for calculating the amplitude coefficient performed by output signal generation unit according to the present embodiments; 
           [0027]      FIG. 21  is a flowchart illustrating a second procedure for calculating the amplitude coefficient performed by the output signal generation unit according to the present embodiments; and 
           [0028]      FIG. 22  is a flowchart illustrating a process for determining the deterioration of the pseudo sound performed by the output signal generation unit according to the present embodiments. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0029]    In embodiments of the present invention, information processing devices  100  to  700  perform interpolation for an audio signal lost by a transmission error occurring in VoIP or the like. Functional configurations of the information processing devices  100  to  700  are illustrated in  FIGS. 1 to 7 . 
         [0030]    The information processing devices  100  to  700  calculate pseudo sound of sound included in an input signal and pseudo noise imitating background noise included in the input signal. The information processing devices  100  to  700  perform interpolation for a packet loss by using an interpolation signal formed by the combination of the pseudo sound and the pseudo noise. Further, the information processing devices  100  to  700  can separately control the pseudo sound and the pseudo noise. Accordingly, the information processing devices  100  to  700  can generate an interpolation signal having high sound quality. The signal loss for which the interpolation is performed by the information processing devices  100  to  700  according to the present embodiments includes, for example, a packet loss caused by congestion of a network, an error occurring on a network line, and an encoding error occurring in encoding an audio signal. 
         [0031]    With reference to  FIGS. 1 to 7 , an overview of functions of the information processing devices  100  to  700  will be described below. 
       Configuration Diagram of Information Processing Device  100   
       [0032]      FIG. 1  is a configuration diagram of the information processing device  100  according to one of the present embodiments. 
         [0033]    The information processing device  100  is constituted by analysis unit  101 , pseudo sound generation unit  102 , pseudo noise generation unit  103 , and output signal generation unit  104 . Furthermore, the information processing device  100  includes a receiving unit for receiving an audio signal and an output unit for outputting an interpolation signal, and the receiving unit and the output unit are not shown in  FIG. 1 . Information processing device  200  to  700  includes a receiving unit and an output unit as well and each receiving unit and output unit are not shown in  FIGS. 1 to 7 . The information processing device  100  is also able to perform a process for interpolating the audio signal in a firmware executed on a CPU mounted on the information processing device  100 . The information processing devices  200  to  700  are able to perform a process for interpolating the audio signal in a firmware executed on a CPU as well. 
         [0034]    The analysis unit  101  calculates the feature quantity of sound and the feature quantity of noise on the basis of error information and an input signal of a normal section input from outside the information processing device  100 . Herein, the error information refers to the information representing the section in which the packet loss has occurred in the transmission of sound. The feature quantity of the sound includes, for example, a sound component of the audio signal, the envelope of the sound component, and the pattern of change in the envelope of the sound component. Further, the feature quantity of the background noise includes, for example, the frequency characteristic of the background noise. Specific examples of the feature quantity of the sound and the feature quantity of the background noise will be described in the description of the information processing devices  200  to  700  illustrated in  FIGS. 2 to 7 . 
         [0035]    Then, the analysis unit  101  inputs the feature quantity of the sound to the pseudo sound generation unit  102 . The pseudo sound generation unit  102  generates the pseudo sound on the basis of the feature quantity of the sound. 
         [0036]    Further, the analysis unit  101  inputs the feature quantity of the noise to the pseudo noise generation unit  103 . The pseudo noise generation unit  103  generates the pseudo noise on the basis of the feature quantity of the noise. 
         [0037]    The pseudo sound generation unit  102  inputs the pseudo sound to the output signal generation unit  104 . The pseudo noise generation unit  103  inputs the pseudo noise to the output signal generation unit  104 . Further, the analysis unit  101  inputs the feature quantity of the sound and the feature quantity of the noise to the output signal generation unit  104 . The output signal generation unit  104  acquires the error information and the input signal from outside the information processing device  100 . Then, the output signal generation unit  104  generates an output signal. Configuration diagram of information processing device  200   
         [0038]      FIG. 2  is a configuration diagram of the information processing device  200  according to one of the present embodiments. 
         [0039]    The information processing device  200  is constituted by analysis unit  201 , pseudo sound generation unit  202 , pseudo noise generation unit  203 , and output signal generation unit  204 . 
         [0040]    The analysis unit  201  calculates the feature quantity of the sound and the feature quantity of the noise on the basis of the error information and the input signal of the normal section input from outside the information processing device  200 . 
         [0041]    Then, the analysis unit  201  inputs the feature quantity of the sound to the pseudo sound generation unit  202 . The pseudo sound generation unit  202  generates the pseudo sound on the basis of the feature quantity of the sound. 
         [0042]    Further, the analysis unit  201  inputs the frequency characteristic of the background noise to the pseudo noise generation unit  203 . The frequency characteristic of the background noise include, for example, the power spectrum, the impulse response, and the filter coefficient of the background noise. Herein, the analysis unit  201  calculates the frequency characteristic of the background noise in accordance with a processing procedure illustrated in  FIG. 9 . The pseudo noise generation unit  203  generates the pseudo noise on the basis of the frequency characteristic of the background noise. For example, the pseudo noise generation unit  203  generates white noise. Then, the pseudo noise generation unit  203  generates the pseudo noise by applying the frequency characteristic of the background noise to the white noise. Alternatively, the pseudo noise generation unit  203  may be configured to previously hold the white noise. Herein, the pseudo noise generation unit  203  generates the pseudo noise in accordance with a processing procedure illustrated in  FIG. 17 . 
         [0043]    The pseudo sound generation unit  202  inputs the pseudo sound to the output signal generation unit  204 . The pseudo noise generation unit  203  inputs the pseudo noise to the output signal generation unit  204 . Further, the analysis unit  201  inputs the feature quantity of the sound and the feature quantity of the noise to the output signal generation unit  204 . The output signal generation unit  204  acquires the error information and the input signal from outside the information processing device  200 . Then, the output signal generation unit  204  generates the output signal. 
       Configuration Diagram of Information Processing Device  300   
       [0044]      FIG. 3  is a configuration diagram of the information processing device  300  according to one of the present embodiments. 
         [0045]    In the information processing device  300 , analysis unit  301  specifically calculates the power spectrum of the background noise as the feature quantity of the noise. 
         [0046]    The information processing device  300  is constituted by the analysis unit  301 , pseudo sound generation unit  302 , pseudo noise generation unit  303 , and output signal generation unit  304 . 
         [0047]    The analysis unit  301  calculates the feature quantity of the sound and the power spectrum of the background noise on the basis of the error information and the input signal of the normal section input from outside the information processing device  300 . The analysis unit  301  calculates the power spectrum of the background noise in accordance with the processing procedure illustrated in  FIG. 9 . 
         [0048]    Then, the analysis unit  301  inputs the feature quantity of the sound to the pseudo sound generation unit  302 . The pseudo sound generation unit  302  generates the pseudo sound on the basis of the feature quantity of the sound. 
         [0049]    Further, the analysis unit  301  inputs the power spectrum of the background noise to the pseudo noise generation unit  303 . The pseudo noise generation unit  303  generates the pseudo noise by providing a random phase to the power spectrum of the background noise and calculating a signal of the time domain through frequency-to-time conversion. Specifically, the pseudo noise generation unit  303  generates the pseudo noise in accordance with a processing procedure illustrated in  FIG. 18 . 
         [0050]    The pseudo sound generation unit  302  inputs the pseudo sound to the output signal generation unit  304 . The pseudo noise generation unit  303  inputs the pseudo noise to the output signal generation unit  304 . Further, the analysis unit  301  inputs the feature quantity of the sound and the feature quantity of the noise to the output signal generation unit  304 . The output signal generation unit  304  acquires the error information and the input signal from outside the information processing device  300 . Then, the output signal generation unit  304  generates the output signal. 
       Configuration Diagram of Information Processing Device  400   
       [0051]      FIG. 4  is a configuration diagram of the information processing device  400  according to one of the present embodiments. 
         [0052]    In the information processing device  400  according to the present embodiment, analysis unit  401  calculates the periodicity of the input signal. 
         [0053]    The information processing device  400  is constituted by the analysis unit  401 , pseudo sound generation unit  402 , pseudo noise generation unit  403 , and output signal generation unit  404 . The information processing device  400  generates the pseudo sound by repeating the input signal with the length of an integral multiple of the period of the input signal. 
         [0054]    The analysis unit  401  calculates the periodicity of the input signal and the feature quantity of the noise on the basis of the error information and the input signal of the normal section input from outside the information processing device  400 . 
         [0055]    Then, the analysis unit  401  inputs the input signal and the periodicity of the input signal to the pseudo sound generation unit  402 . The analysis unit  401  calculates the autocorrelation coefficient of the input signal from Formula (F3). The analysis unit  401  calculates, as the period, the length of a displacement position of the signal for maximizing the autocorrelation coefficient. The procedure for calculating the periodicity will be described later. 
         [0056]    On the basis of the input signal and the periodicity of the input signal, the pseudo sound generation unit  402  generates the pseudo sound by repeating the input signal with the length of the integral multiple of the period. Further, the analysis unit  401  inputs the feature quantity of the noise to the pseudo noise generation unit  403 . The pseudo noise generation unit  403  generates the pseudo noise on the basis of the feature quantity of the noise. 
         [0057]    The pseudo sound generation unit  402  inputs the pseudo sound to the output signal generation unit  404 . The pseudo noise generation unit  403  inputs the pseudo noise to the output signal generation unit  404 . Further, the analysis unit  401  inputs the periodicity of the input signal and the feature quantity of the noise to the output signal generation unit  404 . The output signal generation unit  404  acquires the error information and the input signal from outside the information processing device  400 . Then, the output signal generation unit  404  generates the output signal. 
       Configuration Diagram of Information Processing Device  500   
       [0058]      FIG. 5  is a configuration diagram of the information processing device  500  according to one of the present embodiments. 
         [0059]    The information processing device  500  is constituted by analysis unit  501 , pseudo sound generation unit  502 , pseudo noise generation unit  503 , and output signal generation unit  504 . 
         [0060]    The information processing device  500  generates the pseudo sound by repeating the sound component included in the input signal with the length of an integral multiple of the period of the sound component. 
         [0061]    The analysis unit  501  calculates the sound component included in the input signal, the periodicity of the sound component, and the feature quantity of the noise on the basis of the error information and the input signal of the normal section input from outside the information processing device  500 . 
         [0062]    Then, the analysis unit  501  inputs the sound component and the periodicity of the sound component to the pseudo sound generation unit  502 . The pseudo sound generation unit  502  generates the pseudo sound by repeating the sound component with the length of the integral multiple of the period of the sound component. The analysis unit  501  calculates the sound component in accordance with a procedure for calculating the sound component illustrated in  FIG. 10 . Further, the analysis unit  501  calculates the autocorrelation coefficient of the sound component from Formula (F3). The analysis unit  501  calculates, as the period of the sound component, the length of a displacement position of the signal for maximizing the autocorrelation coefficient. 
         [0063]    Further, the analysis unit  501  inputs the feature quantity of the noise to the pseudo noise generation unit  503 . The pseudo noise generation unit  503  generates the pseudo noise on the basis of the feature quantity of the noise. 
         [0064]    The pseudo sound generation unit  502  inputs the pseudo sound to the output signal generation unit  504 . The pseudo noise generation unit  503  inputs the pseudo noise to the output signal generation unit  504 . Further, the analysis unit  501  inputs the periodicity of the sound component and the feature quantity of the noise to the output signal generation unit  504 . The output signal generation unit  504  acquires the error information and the input signal from outside the information processing device  500 . Then, the output signal generation unit  504  generates the output signal. 
       Configuration Diagram of Information Processing Device  600   
       [0065]      FIG. 6  is a configuration diagram of the information processing device  600  according to one of the present embodiments. 
         [0066]    The information processing device  600  is constituted by analysis unit  601 , pseudo sound generation unit  602 , pseudo noise generation unit  603 , and output signal generation unit  604 . 
         [0067]    The information processing device  600  generates the pseudo sound by repeating the sound source of the sound included in the input signal with the length of an integral multiple of the period of the sound source and applying the envelope of the sound to the sound source. The analysis unit  601  calculates the envelope of the sound and the sound source of the sound in accordance with a procedure for calculating the envelope of the sound and the sound source of the sound, which is illustrated in  FIG. 11 . 
         [0068]    The analysis unit  601  calculates the envelope of the sound included in the input signal, the sound source of the sound, the periodicity of the sound source of the sound, and feature quantity of the noise on the basis of the error information and the input signal of the normal section input from outside the information processing device  600 . 
         [0069]    Then, the analysis unit  601  inputs the envelope of the sound, the sound source of the sound, and the periodicity of the sound source of the sound to the pseudo sound generation unit  602 . The pseudo sound generation unit  602  generates the pseudo sound by repeating the sound source of the sound included in the input signal with the length of the integral multiple of the period of the sound source of the sound and applying the envelope of the sound to the sound source. Further, the analysis unit  601  inputs the feature quantity of the noise to the pseudo noise generation unit  603 . The pseudo noise generation unit  603  generates the pseudo noise on the basis of the feature quantity of the noise. 
         [0070]    The pseudo sound generation unit  602  inputs the pseudo sound to the output signal generation unit  604 . The pseudo noise generation unit  603  inputs the pseudo noise to the output signal generation unit  604 . Further, the analysis unit  601  inputs the periodicity of the sound source of the sound and the feature quantity of the noise to the output signal generation unit  604 . The output signal generation unit  604  acquires the error information and the input signal from outside the information processing device  600 . Then, the output signal generation unit  604  generates the output signal. 
       Configuration Diagram of Information Processing Device  700   
       [0071]      FIG. 7  is a configuration diagram of the information processing device  700  according to one of the present embodiments. 
         [0072]    The information processing device  700  is constituted by analysis unit  701 , pseudo sound generation unit  702 , pseudo noise generation unit  703 , and output signal generation unit  704 . 
         [0073]    The information processing device  700  generates the pseudo sound by repeating the sound source of the sound included in the input signal with the length of an integral multiple of the period of the sound source of the sound and applying to the sound source the pattern of change in the envelope of the sound. 
         [0074]    The analysis unit  701  calculates the pattern of change in the envelope of the sound included in the input signal, the sound source of the sound, the periodicity of the sound source of the sound, and the feature quantity of the noise on the basis of the error information and the input signal of the normal section input from outside the information processing device  700 . The analysis unit  701  calculates the envelope of the sound and the sound source of the sound in accordance with the procedure for calculating the envelope of the sound and the sound source of the sound, which is illustrated in  FIG. 11 . Further, the analysis unit  701  calculates the pattern of change in the envelope of the sound in accordance with a procedure for calculating the pattern of change in the envelope of the sound, which is illustrated in  FIG. 12 . 
         [0075]    Then, the analysis unit  701  inputs the pattern of change in the envelope of the sound, the sound source of the sound, and the periodicity of the sound source of the sound to the pseudo sound generation unit  702 . The pseudo sound generation unit  702  generates the pseudo sound by repeating the sound source of the sound included in the input signal with the length of the integral multiple of the period of the sound source of the sound and applying to the sound source the pattern of change in the envelope of the sound. Further, the analysis unit  701  inputs the feature quantity of the noise to the pseudo noise generation unit  703 . The pseudo noise generation unit  703  generates the pseudo noise on the basis of the feature quantity of the noise. 
         [0076]    The pseudo sound generation unit  702  inputs the pseudo sound to the output signal generation unit  704 . The pseudo noise generation unit  703  inputs the pseudo noise to the output signal generation unit  704 . Further, the analysis unit  701  inputs the periodicity of the sound source of the sound and the feature quantity of the noise to the output signal generation unit  704 . The output signal generation unit  704  acquires the error information and the input signal from outside the information processing device  700 . Then, the output signal generation unit  704  generates the output signal. 
       Procedure of Interpolation Process by Information Processing Devices  100  to  700   
       [0077]      FIG. 8  is a flowchart of the interpolation process performed by the information processing devices  100  to  700  illustrated in  FIGS. 1 to 7 . The flowchart of the interpolation process illustrates schematic process steps performed by the information processing devices  100  to  700 . 
         [0078]    The information processing devices  100  to  700  are devices for performing the interpolation for the signal loss occurring in the transmission of sound through digital signals. Particularly, the information processing devices  100  to  700  according to the present embodiments are devices for performing the interpolation for the packet loss occurring in the transmission of sound in a packet switching network. Further, the information processing devices  100  to  700  receive the input signal frame by frame. 
         [0079]    The information processing devices  100  to  700  receive the error information and the input signal of the current frame input to the information processing devices  100  to  700  (Step  801 ). The input signal is a frame-by-frame digital signal representing the sound and the background noise. 
         [0080]    The information processing devices  100  to  700  determine the presence or absence of an error in the current frame on the basis of the error information (Step  802 ). The error information is the information representing the section in which the packet loss has occurred. The presence of the error indicates that the packet loss has occurred in the input signal, i.e., the packet is “absent.” 
         [0081]    If the information processing devices  100  to  700  determine the absence of the error in the current frame (NO at Step  802 ), the information processing devices  100  to  700  analyze the input signal (Step  803 ). More specifically, the analysis unit  101  to  701  included in the information processing devices  100  to  700  analyze the input signal to calculate the feature quantity of the sound and the feature quantity of the background noise. The information processing devices  100  to  700  generate the pseudo sound and the pseudo noise (Steps  804  and  805 ). Then, the information processing devices  100  to  700  generate the output signal by combining together the pseudo sound and the pseudo noise (Step  806 ). 
         [0082]    If the information processing devices  100  to  700  determine the presence of the error in the current frame (YES at Step  802 ), the information processing devices  100  to  700  generate the pseudo sound (Step  804 ). Then, the information processing devices  100  to  700  generate the pseudo noise (Step  805 ). The information processing devices  100  to  700  generate the output signal by combining (superimposing) together the pseudo sound and the pseudo noise (Step  806 ). 
         [0083]    The information processing devices  100  to  700  generate the pseudo sound and the pseudo noise irrespective of the presence or absence of the packet loss (the presence or absence of the error). Then, if the packet loss is absent, the information processing devices  100  to  700  output the input signal as the output signal (see Step  1905  in  FIG. 19 ). Frequency characteristic of background noise 
         [0084]      FIG. 9  is a flowchart illustrating the processing procedure for calculating the frequency characteristic of the background noise performed by the analysis unit  101  to  701  according to the present embodiments. 
         [0085]    The analysis unit  101  to  701  perform the detection of the sound in the input signal (Step  901 ). Specifically, the analysis unit  101  to  701  perform the detection of the sound in the input signal by comparing the power of the frame with the average power of the noise. Then, the analysis unit  101  to  701  determine whether or not the sound has been detected (Step  902 ). If the analysis unit  101  to  701  have detected the sound (YES at Step  902 ), the analysis unit  101  to  701  calculate the power spectrum of the background noise (Step  905 ). The calculation of the power spectrum of the background noise is also performed when the analysis unit  101  to  701  have not detected the sound (NO at Step  902 ). In this case, the analysis unit  101  to  701  perform time-to-frequency conversion on the input signal (Step  903 ). Specifically, the analysis unit  101  to  701  perform fast Fourier transform or the like. The time-to-frequency conversion is conversion in which the input signal is decomposed for each frequency and converted from the time domain to the frequency domain. Similarly, the frequency-to-time conversion described later is conversion for converting the input signal from the frequency domain to the time domain. The analysis unit  101  to  701  calculate the power spectrum of the input signal (the current frame) from Formula (F1) (Step  904 ). Herein, p i , re i , and im i  represent the power spectrum (dB) of the i-th band, the real part (dB) of the spectrum of the i-th band, and the imaginary part (dB) of the spectrum of the i-th band, respectively. 
         [0086]    Formula 1 
         [0000]        p   i   =p   i =10 log 10  re   i   2   +im   i   2    (F1) 
         [0087]    Then, the analysis unit  101  to  701  calculate the power spectrum of the background noise (Step  905 ). The analysis unit  101  calculates the power spectrum of the background noise of the current frame by weighting and averaging the power spectrum of the current frame and the power spectrum of the background noise of the preceding frame. If the analysis unit  101  to  701  have detected the sound (YES at Step  902 ), the power spectrum of the background noise of the current frame is calculated to be equal to the power spectrum of the background noise of the preceding frame. Herein, n i , prev_n i , and coef represent the power spectrum (dB) of the background noise of the i-th band, the power spectrum (dB) of the background noise of the i-th band in the preceding frame, and the weighting factor of the current frame, respectively. 
         [0088]    Formula 2 
         [0000]        n   i =prev —   n   i *(1−coef)+ p   1 *coef   (F2) 
         [0089]    Alternatively, the analysis unit  101  to  701  may determine the frequency characteristic of the background noise by using an adaptation algorithm, such as a learning identification method. That is, the analysis unit  101  to  701  may calculate the frequency characteristic of the background noise as the filter coefficient learned to minimize the error between the filtered white noise and the background noise. 
       Procedure for Calculating Periodicity 
       [0090]    The periodicity calculated by the analysis unit  101  to  701  is the periodicity of the input signal, the signal of the sound component, or the sound source of the sound. In the present embodiments, the periodicity refers to the period of the target signal (the input signal, the signal of the sound component, or the sound source of the sound) and the strength of the periodicity. In the present embodiments, the strength of the periodicity is represented by the value of the maximum autocorrelation coefficient. The analysis unit  101  to  701  calculate the autocorrelation coefficient of the target signal from Formula (F3). Then, the analysis unit  101  to  701  calculate, as the period, the length of a displacement position of the signal for maximizing the autocorrelation coefficient. Herein, the period and the periodicity are represented as a_max and MAX(corr(a)), respectively. Further, x, M, and a represent the target signal for which the periodicity is calculated, the length (the sample) of the section for which the correlation coefficient is calculated, and the start position of the signal for which the correlation coefficient is calculated, respectively. Further, corr(a), a_max, and i represent the correlation coefficient obtained when the displacement position is represented by the value a, the value of a corresponding to the maximum correlation coefficient (the position maximizing the autocorrelation coefficient), and the index (the sample) of the signal, respectively. 
         [0091]    Formula 3 
         [0000]    
       
         
           
             
               
                 
                   
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       Procedure for Calculating Sound Component 
       [0092]    The analysis unit  501  illustrated in  FIG. 5  calculates the sound component of the input signal.  FIG. 10  is a flowchart of the procedure for calculating the sound component performed by the analysis unit  501  according to one of the present embodiments. Description will be made below of the procedure for calculating the sound component of the input signal performed by the analysis unit  501 . 
         [0093]    The analysis unit  501  receives the input signal input to the information processing device  500 , and performs the detection of the sound and the calculation of the power spectrum of the background noise (Step  1001 ). The detection of the sound and the calculation of the power spectrum of the background noise are performed in accordance with the processing procedure for calculating the frequency characteristic of the background noise illustrated in  FIG. 9 . 
         [0094]    Then, the analysis unit  501  determines whether or not the sound has been detected in the current frame (Step  1002 ). If the analysis unit  501  has detected the sound in the current frame (YES at Step  1002 ), the analysis unit  501  performs the time-to-frequency conversion on the input signal (Step  1003 ). The analysis unit  501  calculates the power spectrum of the input signal (Step  1004 ). The power spectrum of the input signal is calculated from Formula (F1) The analysis unit  501  calculates the power spectrum of the sound (Step  1005 ). The analysis unit  501  calculates the power spectrum of the sound by subtracting the power spectrum of the background noise calculated at Step  1001  from the power spectrum of the input signal calculated at Step  1004 . Alternatively, the analysis unit  501  may be configured to calculate the power spectrum of the sound component by calculating the SNR (signal-to-noise ratio) from the ratio between the power spectrum of the input signal and the power spectrum of the background noise and determining the ratio of the sound component included in the input signal in accordance with the SNR. 
         [0095]    The analysis unit  501  performs the frequency-to-time conversion on the power spectrum of the sound (Step  1006 ). In the present embodiment, inverse Fourier transform is performed as the frequency-to-time conversion. Accordingly, the analysis unit  501  obtains, as the sound component, the signal converted to the time domain. 
         [0096]    Further, if the analysis unit  501  has not detected the sound in the current frame (NO at Step  1002 ), the analysis unit  501  completes the process of calculating the sound component of the input signal. 
       Procedure for Calculating Envelope of Sound and Sound Source of Sound 
       [0097]    The analysis unit  601  and  701  illustrated in  FIGS. 6 and 7  calculate the envelope of the sound in the input signal and the sound source of the sound.  FIG. 11  is a flowchart of the procedure for calculating the envelope of the sound and the sound source of the sound performed by the analysis unit  601  and  701  each according to one of the present embodiments. 
         [0098]    The analysis unit  601  and  701  receive the input signal input to the information processing devices  600  and  700 , respectively (Step  1101 ). The analysis unit  601  and  701  perform the time-to-frequency conversion on the input signal (Step  1102 ). Then, the analysis unit  601  and  701  calculate the logarithmic power spectrum of the input signal (Step  1103 ). 
         [0099]    The analysis unit  601  and  701  perform the frequency-to-time conversion on the logarithmic power spectrum of the input signal (Step  1104 ). The analysis unit  601  and  701  extract high quefrency components and low quefrency components from a signal obtained through the frequency-to-time conversion performed on the logarithmic power spectrum of the input signal (Step  1105 ). The dimension of the quefrencies is time. 
         [0100]    Then, the analysis unit  601  and  701  perform the time-to-frequency conversion on the high quefrency components to calculate the envelope of the sound (Step  1106 ). Further, the analysis unit  601  and  701  perform the time-to-frequency conversion on the low quefrency components to calculate the sound source of the sound (Step  1107 ). 
       Procedure for Calculating Envelope Pattern of Sound 
       [0101]    The analysis unit  701  illustrated in  FIG. 7  calculates the envelope pattern of the sound of the input signal.  FIG. 12  is a flowchart of the procedure for calculating the envelope pattern of the sound performed by the analysis unit  701  according to one of the present embodiments. 
         [0102]    The analysis unit  701  calculates the envelope spectrum of the input signal, and performs the detection of the sound (Step  1201 ). 
         [0103]    The analysis unit  701  calculates formants and antiformants (Step  1202 ). The formants represent the maximum points of the envelope spectrum, while the antiformants represent the minimum points of the envelope spectrum. 
         [0104]    The analysis unit  701  determines whether or not the current frame is the target section for which the envelope pattern is to be recorded (Step  1203 ). If the total number of the formants and the antiformants included in the current frame is equal to or less than a threshold value in a section, or if the sound has not been detected in a section, the analysis unit  701  determines that the section is not the recording target section. That is, the analysis unit  701  determines, as the recording target section, the section in which the total number of the formants and the antiformants included in the current frame is greater than the threshold value. 
         [0105]    If the analysis unit  701  determines that the current frame is the recording target section (YES at Step  1203 ), the analysis unit  701  stores the formants and the antiformants in a memory (Step  1204 ). In the present example, the analysis unit  701  has the memory for storing the formants and the antiformants. 
         [0106]    Meanwhile, if the analysis unit  701  determines that the current frame is not the recording target section (NO at Step  1203 ), the analysis unit  701  clears the stored formants and antiformants from the memory (Step  1205 ). 
       First Procedure for Generating Pseudo Sound 
       [0107]      FIG. 13  is a flowchart of a procedure for generating the pseudo sound performed by the pseudo sound generation unit  102  to  502  each according to one of the present embodiments. Further,  FIG. 14  is a schematic diagram illustrating a connection relationship between repeating signal segments according to one of the present embodiments. Herein, M represents the length (the sample) of the section for which the correlation coefficient is calculated, while L represents the overlapping length. 
         [0108]    The pseudo sound generation unit  102  to  502  receive the target signal to be repeated from the analysis unit  101  to  501 , respectively (Step  1301 ). The target signal to be repeated is the input signal of the normal section or the signal of the sound component of the normal section. The normal section refers to the section in which the error has not occurred, i.e., the section in which the packet loss has not occurred. 
         [0109]    With the use of Formula (F3), the pseudo sound generation unit  102  to  502  calculate the autocorrelation coefficient of the target signal to be repeated (Step  1302 ). To calculate the periodicity of the pseudo sound (the period and the strength of the periodicity of the pseudo sound), the pseudo sound generation unit  102  to  502  calculate the autocorrelation coefficient of the target signal to be repeated. 
         [0110]    Then, the pseudo sound generation unit  102  to  502  calculate the maximum position of the calculated autocorrelation coefficient (Step  1303 ). The maximum position of the autocorrelation coefficient is represented as a_max, and corresponds to the period. 
         [0111]    The pseudo sound generation unit  102  to  502  calculate a signal segment to be repeated (Step  1304 ). Herein, the signal segment to be repeated is a segment extending to the end of the target signal from the position ahead of an autocorrelation coefficient start position by the distance of a sample corresponding to the value a_max+L. 
         [0112]    The pseudo sound generation unit  102  to  502  connect and repeat the repeating signal segments (Step  1305 ). Herein, the pseudo sound generation unit  102  to  502  sequentially connect the repeating signal segments such that a sample corresponding to the value L is overlapped between the adjacent repeating signal segments. With the repeating signal segments connected together with the overlapped portions, the pseudo sound for preventing the occurrence of the abnormal sound can be generated. With the use of Formula (F4), the pseudo sound generation unit  102  to  502  calculate a signal OL reflecting the result of the overlapping of the connected signal segments. Herein, Sl(j) represents a chronologically earlier (left-side) signal to be connected, and Sr(j) represents a chronologically later (right-side) signal to be connected. Further, j represents the number designating a sample, and ranges from zero to L- 1 . 
         [0113]    Formula 4 
         [0000]    
       
         
           
             
               
                 
                   
                     OL 
                      
                     
                       ( 
                       j 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         ( 
                         
                           
                             L 
                             - 
                             j 
                           
                           L 
                         
                         ) 
                       
                        
                       
                         Sl 
                          
                         
                           ( 
                           j 
                           ) 
                         
                       
                     
                     + 
                     
                       
                         j 
                         L 
                       
                        
                       
                         Sr 
                          
                         
                           ( 
                           j 
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   F4 
                   ) 
                 
               
             
           
         
       
     
         [0114]    The pseudo sound generation unit  102  to  502  calculate a signal length obtained as the result of the repeating (the result of the connection) of the repeating signal segments, and determine whether or not the signal length has exceeded a predetermined threshold value (Step  1306 ). 
         [0115]    If the pseudo sound generation unit  102  to  502  determine that the signal length obtained as the result of the repeating has exceeded the predetermined threshold value (YES at Step  1306 ), the pseudo sound generation unit  102  to  502  complete the process of generating the pseudo sound. Meanwhile, if the pseudo sound generation unit  102  to  502  determine that the signal length obtained as the result of the repeating has not exceeded the predetermined threshold value (NO at Step  1306 ), the pseudo sound generation unit  102  to  502  continue to connect the repeating signal segments (Step  1305 ). 
       Second Procedure for Generating Pseudo Sound 
       [0116]      FIG. 15  is a flowchart of a procedure for generating the pseudo sound performed by the pseudo sound generation unit  602  according to one of the present embodiments. 
         [0117]    The pseudo sound generation unit  602  receives the envelope of the sound. Further, the pseudo sound generation unit  602  receives the sound source of the sound and the periodicity of the sound source (Step  1501 ). 
         [0118]    The pseudo sound generation unit  602  repeats the sound source to generate one frame of the sound source (Step  1502 ). The pseudo sound generation unit  602  repeats the sound source in accordance with the processing flow illustrated in  FIG. 13  to generate one frame of the sound source. The pseudo sound generation unit  602  applies the envelope to the repeated sound source to generate the pseudo sound (Step  1503 ). Herein, the pseudo sound generation unit  602  employs the following method as the method for applying the envelope to the repeated sound source. The pseudo sound generation unit  602  performs the time-to-frequency conversion on the repeated sound source to calculate an amplitude spectrum O(k). Then, the pseudo sound generation unit  602  multiplies the calculated amplitude spectrum O(k) by an amplitude spectrum E(k) of the envelope to calculate an amplitude spectrum S(k) of the pseudo sound (see Formula (F5)). Herein, S(k), O(k), and E(k) represent the amplitude spectrum of the pseudo sound of the k-th band, the amplitude spectrum of the repeated sound source of the k-th band, and the amplitude spectrum of the envelope of the k-th band, respectively. The pseudo sound generation unit  602  returns S(k) to the time domain through the frequency-to-time conversion. 
         [0119]    Formula 5 
         [0000]        S ( k )= O ( k )* E ( k )   (F5) 
         [0000]    Third procedure for Generating Pseudo Sound 
         [0120]      FIG. 16  is a flowchart of a procedure for generating the pseudo sound performed by the pseudo sound generation unit  702  according to one of the present embodiments. 
         [0121]    The pseudo sound generation unit  702  receives from the analysis unit  701  the envelope of the sound and the pattern of change in the envelope of the sound. Further, the pseudo sound generation unit  702  receives the sound source of the sound and the periodicity of the sound source (Step  1601 ). 
         [0122]    The pseudo sound generation unit  702  repeats the sound source in accordance with the processing flow illustrated in  FIG. 13  to generate one frame of the sound source (Step  1602 ). 
         [0123]    The pseudo sound generation unit  702  calculates the information of change in the envelope from the pattern of change in the envelope of the sound (Step  1603 ). The pseudo sound generation unit  702  calculates the information of change according to the following method. On the basis of envelope information at a time t and a time t+1, the pseudo sound generation unit  702  calculates the information of change in the envelope occurring between the time t and the time t+1. Herein, the envelope information represents the frequency (Hz) and the amplitude (db) of each of the formants and the antiformants. The frequency and the amplitude of the first formant at the time t are assumed to be F 1   x  and F 1   y , respectively. Further, the frequency and the amplitude of the first formant at the time t+1 are assumed to be (F 1   x +Δx) and (F 1   y +Δy), respectively. Accordingly, the information of change in the first formant (px, py) is represented as px=Δx/x and py=Δy/y. In a similar manner, the information of change is calculated for the other formants and antiformants. Then, the information of change in all formants and antiformants is integrated to represent the information of change in the envelope. 
         [0124]    The pseudo sound generation unit  702  updates the envelope of the sound by using the information of change in the envelope (Step  1604 ). The pseudo sound generation unit  702  calculates the formants and antiformants of the envelope of the sound. The pseudo sound generation unit  702  updates the formants and antiformants by applying the corresponding information of change to each of the formants and antiformants. Then, the pseudo sound generation unit  702  calculates the width corresponding to each of the formants and antiformants. The width of each of the formants is the difference between two frequencies which are located on the right side and left side of the formant, respectively, and at which the power spectrum first falls below the power spectrum of the formant by a predetermined value. Herein, the predetermined value is 3 dB, for example. Similarly, the width of each of the antiformants is the difference between two frequencies which are located on the right side and left side of the antiformant, respectively, and at which the power spectrum first exceeds the power spectrum of the antiformant by a predetermined value. Specifically, when the frequency and the amplitude of the first formant are F 1 _cur_x and F 1 _cur_y, respectively, the frequency F 1 _cur_x′ and the amplitude F 1 _cur_y′ of the updated first formant can be represented as F 1 _cur_x′=F 1 _cur_x*px and F 1 _cur_y′=F 1 _cur_y*py, respectively. The other formants and antiformants can be updated in a similar manner. The pseudo sound generation unit  702  calculates the envelope of the sound by applying a quadratic curve to each of the formants and antiformants. The quadratic curve applied to each of the formants by the pseudo sound generation unit  702  is a quadratic curve having maximum coordinates (fx, fy) and passing through coordinates (fx+0.5 WF, fy−3). Herein, (fx, fy) and WF (Hz) represent the position and the width of the formant, respectively. Further, the x-axis and the y-axis represent the frequency (Hz) and the power (dB), respectively. Similarly, the quadratic curve applied to each of the antiformants by the pseudo sound generation unit  702  is a quadratic curve having minimum coordinates (ux, uy) and passing through coordinates (ux+0.5 UF, uy+3). Herein, (ux, uy) and UF (Hz) represent the position and the width of the antiformant, respectively. Further, the pseudo sound generation unit  702  interpolates the quadratic curve corresponding to the formant and the quadratic curve corresponding to the antiformant to calculate the envelope of the border between the formant and the antiformant. 
         [0125]    The pseudo sound generation unit  702  applies the updated envelope to the repeated sound source to generate the pseudo sound (Step  1605 ). The pseudo sound generation unit  702  generates the pseudo sound by employing a method similar to the method employed by the pseudo sound generation unit  602 . That is, the pseudo sound generation unit  702  calculates the amplitude spectrum O(k) by performing the time-to-frequency conversion on the repeated sound source. The pseudo sound generation unit  702  multiplies the calculated amplitude spectrum O(k) by the amplitude spectrum E(k) of the envelope to calculate the amplitude spectrum S(k) of the pseudo sound (see Formula (F5)). Then, the pseudo sound generation unit  702  returns S(k) to the time domain through the frequency-to-time conversion to generate the pseudo sound. 
       First Procedure for Generating Pseudo Noise 
       [0126]      FIG. 17  is a flowchart illustrating the procedure for generating the pseudo noise performed by the pseudo noise generation unit  203  according to one of the present embodiments. 
         [0127]    The pseudo noise generation unit  203  generates the white noise (Step  1701 ). 
         [0128]    With the use of Formula (F6), the pseudo noise generation unit  203  applies to the white noise the filter coefficient representing the frequency characteristic of the background noise, to thereby generate the pseudo noise (Step  1702 ). Herein, y(n), w(n), h(m), n, and m represent the pseudo noise, the white noise, the filter coefficient, the number of samples, and the filter order ranging from zero to p−1, respectively. 
         [0129]    Formula 6 
         [0000]    
       
         
           
             
               
                 
                   
                     y 
                      
                     
                       ( 
                       n 
                       ) 
                     
                   
                   = 
                   
                     
                       ∑ 
                       
                         m 
                         = 
                         0 
                       
                       
                         p 
                         - 
                         1 
                       
                     
                      
                     
                       
                         h 
                          
                         
                           ( 
                           m 
                           ) 
                         
                       
                        
                       
                         w 
                          
                         
                           ( 
                           
                             n 
                             - 
                             m 
                           
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   F6 
                   ) 
                 
               
             
           
         
       
     
       Second Procedure for Generating Pseudo Noise 
       [0130]      FIG. 18  is a flowchart of the procedure for generating the pseudo noise performed by the pseudo noise generation unit  303  according to one of the present embodiments. 
         [0131]    The pseudo noise generation unit  303  receives the power spectrum of the background noise from the analysis unit  301  (Step  1801 ). 
         [0132]    The pseudo noise generation unit  303  randomizes the phase of the spectrum of the background noise (Step  1802 ). Specifically, the pseudo noise generation unit  303  randomizes the phase of the background noise while maintaining the magnitude of the amplitude spectrum of the background noise. The amplitude spectrum, the real part of the spectrum of each band, and the imaginary part of the spectrum of each band are represented as s(i), re(i), and im(i), respectively. The pseudo noise generation unit  303  replaces re(i) and im(i) with random numbers re′(i) and im′(i), respectively, and multiplies the random numbers re′(i) and im′(i) by a coefficient to maintain the magnitude of the amplitude spectrum, to thereby calculate the spectrum of the phase-randomized background noise ((αre′(i), αim′(i)). Accordingly, the pseudo amplitude spectrum can be calculated from Formula (F7). 
         [0133]    Formula 7 
         [0000]        s ( i )=√{square root over ((α re ′( i )) 2 +(α im′ ( i )) 2  )}{square root over ((α re ′( i )) 2 +(α im′ ( i )) 2  )}  (F7) 
         [0134]    Then, the pseudo noise generation unit  303  returns the spectrum of the phase-randomized background noise ((αre′(i), αim′(i)) to the time domain through the frequency-to-time conversion to generate the pseudo noise (Step  1803 ). 
       Procedure for Generating Output Signal 
       [0135]      FIG. 19  is a flowchart of a procedure for generating the output signal performed by the output signal generation unit  104  to  704  according to the present embodiments. 
         [0136]    The output signal generation unit  104  to  704  receive the error information, the input signal, the pseudo sound, the pseudo noise, the feature quantity of the sound, and the feature quantity of the noise (Step  1901 ). 
         [0137]    The output signal generation unit  104  to  704  determine the presence or absence of the error on the basis of the information received at Step  1901  (Step  1902 ). 
         [0138]    If the output signal generation unit  104  to  704  determine the presence of the error in the current frame (YES at Step  1902 ), the output signal generation unit  104  to  704  calculate the amplitude coefficient of each of the pseudo sound and the pseudo noise (Step  1903 ). The output signal generation unit  104  to  704  generate the output signal by superimposing together the pseudo sound and the pseudo noise (Step  1904 ). 
         [0139]    If the output signal generation unit  104  to  704  determine the absence of the error in the current frame (NO at Step  1902 ), the output signal generation unit  104  to  704  determine the input signal as the output signal (Step  1905 ). 
       First Procedure for Calculating Amplitude Coefficient 
       [0140]      FIG. 20  is a flowchart illustrating a first procedure for calculating the amplitude coefficient performed by the output signal generation unit  104  to  704  according to the present embodiments. 
         [0141]    The output signal generation unit  104  to  704  determine whether or not the current frame is an error start frame (Step  2001 ). The error start frame refers to the frame in which the frame loss (the packet loss) has first occurred in a section in which the frame loss has occurred. If the output signal generation unit  104  to  704  determine that the current frame is the error start frame (YES at Step  2001 ), the output signal generation unit  104  to  704  perform the sound detection process on the input signal (Step  2002 ). The sound detection process is the process of determining the sound according to whether or not the power of the input signal has exceeded a threshold value. Meanwhile, if the output signal generation unit  104  to  704  determine that the current frame is not the error start frame (NO at Step  2001 ), the output signal generation unit  104  to  704  determine the presence or absence of the sound in the current frame (Step  2003 ). 
         [0142]    At Step  2003 , the output signal generation unit  104  to  704  determine whether or not the sound has been detected (Step  2003 ). If the output signal generation unit  104  to  704  have detected the sound (YES at Step  2003 ), the output signal generation unit  104  to  704  calculate the amplitude coefficient of the pseudo sound and the amplitude coefficient of the pseudo noise as 1−i/R and i/R, respectively (Step  2004 ). Herein, R and i represent the number of samples required to adjust the amplitude of the pseudo sound to zero and the number of samples appearing after the start of the error, respectively. The value R is a preset value which has been previously determined. Meanwhile, if the output signal generation unit  104  to  704  have not detected the sound (NO at Step  2003 ), the output signal generation unit  104  to  704  calculate the amplitude coefficient of the pseudo sound and the amplitude coefficient of the pseudo noise as zero and one, respectively (Step  2005 ). 
         [0143]    The output signal generation unit  104  to  704  generate the output signal by adding together the pseudo sound multiplied by the amplitude coefficient therefor and the pseudo noise multiplied by the amplitude coefficient therefor (Step  2006 ). Herein, the output signal generation unit  104  to  704  perform adjustment such that the intra-frame average amplitude of the input signal immediately preceding the error becomes equal to the intra-frame average amplitude of the output signal obtained by adding together the pseudo sound multiplied by the amplitude coefficient therefor and the pseudo noise multiplied by the amplitude coefficient therefor. 
       Second Procedure for Calculating Amplitude Coefficient 
       [0144]      FIG. 21  is a flowchart illustrating a second procedure for calculating the amplitude coefficient performed by the output signal generation unit  104  to  704  according to the present embodiments. 
         [0145]    The output signal generation unit  104  to  704  determine whether or not the current frame is the error start frame (Step  2101 ). If the output signal generation unit  104  to  704  determine that the current frame is the error start frame (YES at Step  2101 ), the output signal generation unit  104  to  704  perform the sound detection process on the input signal (Step  2102 ). The sound detection process according to the present embodiment is also the process of determining the sound according to whether or not the power of the input signal has exceeded the threshold value. Meanwhile, if the output signal generation unit  104  to  704  determine that the current frame is not the error start frame (NO at Step  2101 ), the output signal generation unit  104  to  704  determine the presence or absence of the sound in the current frame. 
         [0146]    The output signal generation unit  104  to  704  determine whether or not the sound has been detected (Step  2103 ). If the output signal generation unit  104  to  704  have detected the sound (YES at Step  2103 ), the output signal generation unit  104  to  704  perform a deterioration determination process on the pseudo sound (Step  2104 ). 
         [0147]    The output signal generation unit  104  to  704  determine whether or not the pseudo sound has been deteriorated (Step  2105 ). If the output signal generation unit  104  to  704  determine that the pseudo sound has not been deteriorated (NO at Step  2105 ), the output signal generation unit  104  to  704  calculate the amplitude coefficient of the pseudo sound and the amplitude coefficient of the pseudo noise as 0.5 and 0.5, respectively (Step  2106 ). If the output signal generation unit  104  to  704  determine that the pseudo sound has been deteriorated (YES at Step  2105 ), the output signal generation unit  104  to  704  calculate the amplitude coefficient of the pseudo sound and the amplitude coefficient of the pseudo noise as 1−i/Q and i/Q, respectively (Step  2107 ). Herein, Q and i represent the number of samples required to adjust the amplitude of the pseudo sound to zero after the determination of the deterioration of the pseudo sound and the number of samples appearing after the determination of the deterioration of the pseudo sound, respectively. Further, the amplitude coefficient of the pseudo sound may be weighted as follows by the periodicity of the input signal, the periodicity of the sound component, or the periodicity of the sound source. For example, the amplitude coefficient of the pseudo sound may be weighted as (1−i/Q)*MAX(corr(a)). 
         [0148]    At Step  2103 , if the output signal generation unit  104  to  704  have not detected the sound (NO at Step  2103 ), the output signal generation unit  104  to  704  calculate the amplitude coefficient of the pseudo sound and the amplitude coefficient of the pseudo noise as zero and one, respectively (Step  2108 ). 
         [0149]    The output signal generation unit  104  to  704  generate the output signal by adding together the pseudo sound multiplied by the amplitude coefficient therefor and the pseudo noise multiplied by the amplitude coefficient therefor (Step  2109 ). Herein, the output signal generation unit  104  to  704  perform adjustment such that the intra-frame average amplitude of the input signal immediately preceding the error becomes equal to the intra-frame average amplitude of the output signal obtained by adding together the pseudo sound multiplied by the amplitude coefficient therefor and the pseudo noise multiplied by the amplitude coefficient therefor. 
       Procedure for Determining Deterioration of Pseudo Sound 
       [0150]      FIG. 22  is a flowchart illustrating the process of determining the deterioration of the pseudo sound performed by the output signal generation unit  104  to  704  according to the present embodiments. 
         [0151]    The output signal generation unit  104  to  704  calculate the magnitude P 1  (dB) of the repeating period component of the input signal (Step  2201 ). The output signal generation unit  104  to  704  calculate the power spectrum of the input signal by performing the time-to-frequency conversion on the input signal. Then, on the basis of the power spectrum of the input signal, the output signal generation unit  104  to  704  calculate the magnitude (the power) P 1  of the repeating period component of the input signal. 
         [0152]    The output signal generation unit  104  to  704  calculate the magnitude P 2  (dB) of the repeating period component of the pseudo sound (Step  2202 ). The output signal generation unit  104  to  704  calculate the power spectrum of the pseudo sound by performing the time-to-frequency conversion on the pseudo sound. Then, on the basis of the power spectrum of the pseudo sound, the output signal generation unit  104  to  704  calculate the magnitude (the power) P 2  of the repeating period component of the pseudo sound. 
         [0153]    The output signal generation unit  104  to  704  subtract the magnitude P 1  of the repeating period component of the input signal from the magnitude P 2  of the repeating period component of the pseudo sound to calculate the value P 2 −P 1 . Then, the output signal generation unit  104  to  704  determine whether or not the value P 2 −P 1  has exceeded a preset predetermined threshold value (Step  2203 ). If the output signal generation unit  104  to  704  determine that the value P 2 −P 1  has not exceeded the preset predetermined threshold value (NO at Step  2203 ), the output signal generation unit  104  to  704  determine that the pseudo sound has not been deteriorated (Step  2204 ). Meanwhile, if the output signal generation unit  104  to  704  determine that the value P 2 −P 1  has exceeded the preset predetermined threshold value (YES at Step  2203 ), the output signal generation unit  104  to  704  determine that the pseudo sound has been deteriorated (Step  2205 ). 
       Functions of Information Processing Devices  100  to  700   
       [0154]    The information processing devices  100  to  700  according to the present embodiments separately generate the pseudo sound and the pseudo noise on the basis of the feature quantity of the sound included in the input signal and the feature quantity of the noise included in the input signal. Accordingly, even if the signal immediately preceding the packet loss is a signal having a small periodicity, such as the signal of a consonant, background noise, and so forth, it is possible to perform interpolation for the packet loss while reducing the deterioration of the sound quality caused by abnormal sound and so forth generated by the occurrence of an unnatural period. 
         [0155]    In the above-described manner, the information processing devices  100  to  700  according to the present embodiments analyze the input signal to calculate the feature quantity of the sound included in the input signal and the feature quantity of the background noise included in the input signal. The information processing devices  100  to  700  separately generate the pseudo sound and the pseudo noise by using the feature quantity of the sound and the feature quantity of the background noise. Further, the information processing devices  100  to  700  generate the output signal by distributing the pseudo sound and the pseudo noise in accordance with the characteristics of the input signal. Accordingly, it is possible to perform interpolation which suppresses the deterioration of the sound quality and thus provides high sound quality. 
         [0156]    Further, the information processing device  200  according to one of the present embodiments generates the pseudo noise by using the frequency characteristic of the background noise. Accordingly, it is possible to generate the pseudo noise without causing discontinuation of the sound quality and the power of the pseudo noise from the sound quality and the power of the background noise superimposed on the input signal. 
         [0157]    Further, the information processing device  400  calculates the periodicity of the input signal. Therefore, the distribution of the pseudo sound can be determined in accordance with the periodicity of the input signal. Accordingly, particularly when the periodicity of the input signal is small, the information processing device  400  can suppress abnormal sound attributed to the repetition of the target signal. 
         [0158]    Further, the information processing device  500  according to one of the present embodiments calculates the periodicity of the sound component of the input signal. Therefore, the distribution of the pseudo sound can be determined in accordance with the periodicity of the sound component of the input signal. Accordingly, particularly when the periodicity of the sound component of the input signal is small, the information processing device  500  can suppress abnormal sound attributed to the repetition of the target signal (the sound component of the input signal). Further, the information processing device  500  repeats only the sound component of the input signal. Therefore, abnormal sound attributed to the periodic repetition of the superimposed noise can be suppressed. 
         [0159]    Further, the information processing devices  600  and  700  calculate the periodicity of the sound source of the sound. Therefore, the distribution of the pseudo sound can be determined in accordance with the periodicity of the sound source of the sound. Accordingly, when the periodicity of the sound source of the sound is small, the information processing devices  600  and  700  can suppress abnormal sound attributed to the repetition of the target signal. 
         [0160]    Further, the information processing device  700  calculates the pattern of change in the envelope of the sound. Therefore, the pseudo sound can be generated with the use of the pattern of change in the envelope of the sound. Accordingly, the information processing device  700  can generate more natural pseudo sound, and thus can perform high-quality interpolation.