Patent Publication Number: US-8532986-B2

Title: Speech signal evaluation apparatus, storage medium storing speech signal evaluation program, and speech signal evaluation method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2009-76186, filed on Mar. 26, 2009, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate to a speech signal evaluation apparatus for evaluating a speech signal, a storage medium storing a speech signal evaluation program, and a method for evaluating a speech signal. 
     BACKGROUND 
     For example, Japanese Unexamined Patent Application Publication No. 2001-309483 and No. 7-84596 discuss techniques for objective evaluation of speech quality using an original speech signal without noise and a target speech signal to be evaluated. 
     SUMMARY 
     According to an aspect of the invention, a speech signal evaluation apparatus includes: an acquisition unit that acquires, as a first frame, a speech signal of a specified length from speech signals stored in a storage unit; a first detection unit that detects, on the basis of a speech condition indicating the presence of speech in a frame, whether the first frame is voiced or unvoiced; a variation calculation unit that, when the first frame is unvoiced, calculates a variation in a spectrum associated with the first frame on the basis of the spectrum of the first frame and the spectrum of a second frame that is unvoiced and precedes the first frame in time; and a second detection unit that detects, on the basis of a non-stationary condition based on the variation in spectrum, whether the variation associated with the first frame satisfies the non-stationary condition. An unvoiced frame is a frame that does not satisfy the speech condition, and a voiced frame is a frame that satisfies the speech condition. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram illustrating functions of a speech signal evaluation apparatus according to an embodiment; 
         FIG. 2  is a block diagram illustrating the configuration of the speech signal evaluation apparatus according to the embodiment; 
         FIG. 3  is a flowchart illustrating an operation of the speech signal evaluation apparatus according to the embodiment; 
         FIG. 4  is a diagram illustrating the waveforms of speech signals and label data; 
         FIG. 5  is a diagram illustrating spectrum time change rate differences obtained by a third process of setting a non-stationary determination threshold value; 
         FIG. 6  is a flowchart illustrating an operation of the speech signal evaluation apparatus in the use of the third process of setting a non-stationary determination threshold value; 
         FIG. 7  is a waveform diagram illustrating long segments and short segments; 
         FIG. 8  is a waveform diagram illustrating spectrum time change rates displayed in time series; and 
         FIG. 9  is a diagram illustrating a computer system to which the embodiment is applied. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     According to a conventional evaluation test, original speech is subjected to speech signal processing, such as, for example, directional sound reception and noise reduction, and the resultant speech (processed speech) is compared to the original speech, thus evaluating the processed speech. In many cases, original speech to be used for comparison exists in a voiced segment included in processed speech. As for an unvoiced segment, e.g., a noise segment, however, original speech to be used for comparison does not exist in such an unvoiced segment in many cases. According to a system of comparing original speech with processed speech to evaluate the processed speech, if there is no original speech to be used for comparison in an unvoiced segment included in processed speech, the quality of the processed speech cannot be evaluated. 
     An embodiment is described below with reference to the drawings. 
     The configuration of a speech signal evaluation apparatus according to the present embodiment is now described. 
       FIG. 1  is a block diagram illustrating functions of the speech signal evaluation apparatus according to the present embodiment. The speech signal evaluation apparatus, indicated at  1 , includes an acquisition unit  10 , a segment determination unit  11 , a segment amplitude ratio calculation unit  12 , a fast Fourier transform (FFT) unit  13 , an amplitude spectrum calculation unit  14 , a time change rate calculation unit  15 , a non-stationary rate calculation unit  16 , a time change rate display unit  17 , and a non-stationary rate display unit  18 . 
       FIG. 2  is a block diagram illustrating the configuration of the speech signal evaluation apparatus according to the present embodiment. A computer  800  includes a central processing unit (CPU)  801 , a storage unit  802 , a display unit  803 , and an operation unit  804 . 
     The storage unit  802 , e.g., a memory or other computer-readable medium, stores an executable speech signal evaluation program representing the functions of the speech signal evaluation apparatus  1 . The CPU  801  executes the speech signal evaluation program stored in the storage unit  802  to implement operations performed by the speech signal evaluation apparatus  1 . The operations cause the computer  800  to function as the speech signal evaluation apparatus  1 . 
     The operation unit  804  (e.g., a mouse, keyboard, etc.) acquires an instruction from a user. An output unit outputs a result of evaluation by the speech signal evaluation program or the speech signal evaluation apparatus. For example, the display unit  803  displays a result of evaluation by the speech signal evaluation program or the speech signal evaluation apparatus  1 . The storage unit  802  stores target data to be evaluated (hereinafter, “evaluation target data”), the data serving as a speech signal, which may have been previously recorded. 
     An operation of the speech signal evaluation apparatus  1  is described below. 
       FIG. 3  is a flowchart illustrating the method (e.g., operations and processes) of the speech signal evaluation apparatus  1  according to the present embodiment. 
     Speech signals which serve as target evaluation data items in the present embodiment may include not only speech signals subjected to speech signal processing but also typical speech signals, which include noise. The acquisition unit  10  reads evaluation target data included in the storage unit  802  on a frame-by-frame basis, each frame having a specified length. The segment determination unit  11  makes a determination on each read frame on the basis of a speech condition as to whether the frame is a voiced segment or unvoiced segment. The segment determination unit  11  writes the result of determination as label data into the storage unit  802  (S 11 ). As for an example of the speech condition, when the amplitude of the waveform of the evaluation target data is equal to or greater than a voiced threshold value, the segment determination unit  11  determines that the read frame is a voiced segment in which speech exists. Whereas, when the amplitude of the waveform does not exceed the voiced threshold value, the segment determination unit  11  determines that the frame is an unvoiced segment in which speech does not exist. The length of a frame to be read by the acquisition unit  10  corresponds to the length of FFT by the FFT unit  13 , for example, 2 N  (N is an integer). For instance, assuming that a sampling frequency of evaluation target data is 8000 Hz and the length of a frame is set to 256, one frame is 32 msec. 
       FIG. 4  is a diagram illustrating example waveforms of speech signals and label data. In  FIG. 4 , the axis of abscissa indicates time and the axis of ordinate represents the amplitude. V and U each indicate label data. A segment indicated by “V” is a voiced segment and a segment indicated by “U” is an unvoiced segment. The voiced segment is considered to include both speech and noise. The unvoiced segment is considered to not include speech. In other words, the unvoiced segment is considered to include only noise. Each segment U may include many frames. Similarly, each segment V may include many frames. Although the boundary between each U segment and the adjoining V segment matches a boundary between frames in some cases, the boundary between the U and V segments does not necessary match a boundary between frames. 
     The acquisition unit  10  reads one frame from evaluation target data with written label data from the storage unit  802 . The FFT unit  13  performs FFT on the read frame to convert the frame into a frequency domain signal and writes the obtained signal into the storage unit  802  (S 21 ). Hereinafter, the read frame is referred to as a “current frame”. If YES in S 23 , (alternatively, if NO in S 44  described later) the acquisition unit  10  reads a frame next to the current frame as a new current frame to be processed in the following S 21 . The speech signal evaluation apparatus  1  performs the processing in S 21  and the subsequent processing on the new current frame, serving as a process target. 
     The amplitude spectrum calculation unit  14  reads the frequency domain signal from the storage unit  802 . The amplitude spectrum calculation unit  14  calculates the amplitude spectrum of the read frequency domain signal and writes the calculated amplitude spectrum into the storage unit  802  (S 22 ). 
     The time change rate calculation unit  15  reads label data related to the current frame from the storage unit  802  and determines, on the basis of the read label data, whether the current frame is a voiced segment (S 23 ). When the current frame is a voiced segment (YES in S 23 ), the time change rate calculation unit  15  terminates the processing being performed on the current frame, and the method returns to S 21 . 
     When the current frame is an unvoiced segment (NO in S 23 ), the time change rate calculation unit  15  reads the amplitude spectrum of a first unvoiced frame, serving as the current frame, from the storage unit  802 . In addition, the time change rate calculation unit  15  reads the amplitude spectrum of a preceding frame, serving as an unvoiced frame, just previous to the current frame from the storage unit  802 . The preceding frame is referred to herein as a second unvoiced frame. The time change rate calculation unit  15  calculates the time rate of change of spectrum (hereinafter, “spectrum time change rate”) to be associated with the current frame on the basis of both of the read amplitude spectra and writes the calculated spectrum time change rate into the storage unit  802  (S 24 ). In this embodiment, the spectrum time change rate is used as an example of the amount of change of spectrum. The spectrum time change rate is a value based on the amount of change from the amplitude spectrum of the current frame from that of the preceding frame. 
     The segment amplitude ratio calculation unit  12  calculates the ratio (hereinafter, “segment amplitude ratio”) of the amplitudes of voiced segments to those of unvoiced segments in the whole of evaluation target data items, for example. As an alternative, the calculation of the segment amplitude ratio may be performed not on the whole of the evaluation target data items but on data items between the current frame and a frame that is several seconds older than the current frame of the evaluation target data items. Furthermore, the segment amplitude ratio calculation unit  12  determines a non-stationary determination threshold value for a non-stationary determination on the basis of the segment amplitude ratio (S 31 ). If the volumes of unvoiced segments are low on the whole and the ratio of the amplitudes of voiced segments to those of the unvoiced segments is large, the sensitivity to the spectrum time change rate is too high. Accordingly, the segment amplitude ratio calculation unit  12  sets a non-stationary determination threshold value. 
     The non-stationary rate calculation unit  16  determines, on the basis of a non-stationary condition, whether the current frame is a non-stationary frame. As for an example of the non-stationary condition, the non-stationary rate calculation unit  16  determines whether the spectrum time change rate associated with the current frame exceeds the non-stationary determination threshold value (S 41 ). If the spectrum time change rate of the current frame exceeds the non-stationary determination threshold value (YES in S 41 ), the non-stationary rate calculation unit  16  determines that the current frame is a non-stationary frame (S 42 ). If NO in S 41 , the non-stationary rate calculation unit  16  determines that the current frame is a stationary frame (S 43 ). In this instance, the non-stationary frame is a frame in which a speech signal is non-stationary. For example, when speech signal processing is performed on original speech, musical noise occurs in some cases. The musical noise is an example of non-stationary noises. A stationary frame is a frame in which a speech signal is stationary. 
     The non-stationary rate calculation unit  16  determines whether the above-described processing on all frames is finished (S 44 ). If the above-described processing on all the frames is not finished (NO in S 44 ), the non-stationary rate calculation unit  16  returns the method shown in  FIG. 3  to S 21  and allows the next frame to be subjected to the above-described processing. 
     When the above-described processing on all of the frames is finished (YES in S 44 ), the non-stationary rate calculation unit  16  calculates the number of frames determined as non-stationary in unvoiced segments by the total number of frames in the unvoiced segments. The obtained value is a non-stationary rate (S 51 ). Alternatively, the non-stationary rate calculation unit  16  may divide the number of frames determined as stationary in the unvoiced segments by the total number of frames in the unvoiced segments. 
     The time change rate display unit  17  reads the spectrum time change rates from the storage unit  802  and displays the read rates in time series. The non-stationary rate display unit  18  displays the non-stationary rate as an evaluation value (S 52 ). 
     The method (e.g., processes or operations) of the speech signal evaluation apparatus  1  is then terminated. 
     An operation of the above-described time change rate calculation unit  15  is described in greater detail below. 
     A first process of calculating a spectrum time change rate, a second process of calculating a spectrum time change rate, and a third process of calculating a spectrum time change rate, namely, three kinds of processes are now described as examples of the operation of the time change rate calculation unit  15 . Let t denote time, let i denote a sample number indicating a frequency, and let A(t, i) be an amplitude spectrum in an angular frequency ω(i). 
     In the first process of calculating a spectrum time change rate, the time change rate calculation unit  15  performs the following calculations. The difference between the amplitude spectrum of the current frame and that of the preceding frame at each frequency is calculated as a spectrum difference. The sum of spectrum differences at all frequencies is obtained as F 11 . The sum of spectrum amplitudes of the current frame at all the frequencies is calculated as F 12 . F 11  is divided by F 12 , thus obtaining a value indicating a spectrum time change rate. The spectrum time change rate at time t is expressed by the following equation. 
     
       
         
           
             
               
                 
                   
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     In the second process of calculating a spectrum time change rate, the time change rate calculation unit  15  performs the following calculations. The difference between the amplitude spectrum of the current frame and that of the preceding frame at each frequency is calculated as a spectrum difference. A maximum value of spectrum differences at all the frequencies is multiplied by the frame length, thus obtaining a value F 21 . The sum of spectrum amplitudes of the current frame at all the frequencies is calculated as F 22 . F 21  is divided by F 22 , thus obtaining a value indicating a spectrum time change rate. Let Max ( ) be a function for calculating a maximum value, the spectrum time change rate at time t is expressed by the following equation. 
     
       
         
           
             
               
                 
                   
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     In the third process of calculating a spectrum time change rate, the time change rate calculation unit  15  performs the following calculations. The difference between the amplitude spectrum of the current frame and that of the preceding frame at each frequency is calculated as a spectrum difference. The spectrum difference is multiplied by a weighting factor α based on auditory characteristics, thus obtaining a weighted spectrum difference. The sum of weighted spectrum differences at all the frequencies is calculated as F 31 . The sum of spectrum amplitudes of the current frame at all the frequencies is calculated as F 32 . F 31  is divided by F 32 , thus obtaining a spectrum time change rate. The spectrum time change rate at time t is expressed by the following equation. 
     
       
         
           
             
               
                 
                   
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     An operation of the above-described segment amplitude ratio calculation unit  12  is described in greater detail below. 
     A first process of setting a non-stationary determination threshold values, a second process of setting a non-stationary determination threshold value, and a third process of setting a non-stationary determination threshold value, namely, three kinds of processes are described as examples of a method for setting a non-stationary determination threshold value by the segment amplitude ratio calculation unit  12 . 
     In the first process of setting a non-stationary determination threshold value, the segment amplitude ratio calculation unit  12  compares the segment amplitude ratio with a segment amplitude ratio threshold value to determine a non-stationary determination threshold value. For example, when the segment amplitude ratio is greater than the segment amplitude ratio threshold value, the segment amplitude ratio calculation unit  12  sets the non-stationary determination threshold value to 100. When the segment amplitude ratio is less than the segment amplitude ratio threshold value, the segment amplitude ratio calculation unit  12  sets the non-stationary determination threshold value to 70. 
     In the second process of setting a non-stationary determination threshold value, the segment amplitude ratio calculation unit  12  compares the segment amplitude ratio with a segment amplitude ratio threshold value to determine a non-stationary determination threshold value. For example, when letting x be the segment amplitude ratio, a non-stationary determination threshold value y is expressed by the following equation.
 
 y=f ( x )  (4)
 
     The function f(x) is expressed using the constant α of proportion by the following equation.
 
 y=α×x   (5)
 
     The third process of setting a non-stationary determination threshold value is now described. The amplitude (extent) of variation in the spectrum time change rate in a stationary state varies depending on the kind of noise. A noise with a large variation in the spectrum time change rate differs in auditory perception from a noise with a small variation in the spectrum time change rate, though these noises have the same spectrum time change rate. In the third process of setting a non-stationary determination threshold value, in order to allow a non-stationary determination threshold value to reflect the difference in auditory perception, the segment amplitude ratio calculation unit  12  sets a non-stationary determination threshold value on the basis of the amplitude of variation in the spectrum time change rate. 
     The segment amplitude ratio calculation unit  12  performs the following calculations. A mean of the spectrum time change rates of all frames in unvoiced segments is calculated as a mean spectrum time change rate. The difference between the spectrum time change rate of each frame and the mean spectrum time change rate is calculated as a spectrum time change rate difference. A mean of spectrum time change rate differences of all the frames in the unvoiced segments is calculated as a mean difference z. 
       FIG. 5  is a diagram illustrating spectrum time change rate differences obtained by the third process of setting a non-stationary determination threshold value.  FIG. 5  shows the spectrum time change rate plotted against time.  FIG. 5  further illustrates a mean spectrum time change rate, a spectrum time change rate difference D 1  at time T 1 , and a spectrum time change rate difference D 2  at time T 2 . 
     The non-stationary determination threshold value y is expressed by the following equation.
 
 y=f ( z )  (6)
 
     The function f(z) is expressed using, for example, the constant β of proportion by the following equation.
 
 y=β×z   (7)
 
     An operation of the speech signal evaluation apparatus  1  in the use of the third process of setting a non-stationary determination threshold value is described below. 
       FIG. 6  is a flowchart illustrating the operation (process) of the speech signal evaluation apparatus  1  in the use of the third process of setting a non-stationary determination threshold value. 
     S 11  to S 24  are the same as those in the flowchart of  FIG. 3  and thus, the description of S 11  to S 24  is not repeated herein for the sake of brevity. 
     The segment amplitude ratio calculation unit  12  determines whether the S 21  to S 24  processing on all frames is finished (S 25 ). If the S 21  to S 24  processing on all the frames is not finished (NO in S 25 ), the segment amplitude ratio calculation unit  12  returns the process to S 21  and allows the next frame to be subjected to the S 21  to S 24  processing. 
     When the S 21  to S 24  processing on all the frames is finished (YES in S 25 ), the segment amplitude ratio calculation unit  12  determines a non-stationary determination threshold value using the above-described third process of setting a non-stationary determination threshold value (S 32 ). 
     S 41  to S 43  are the same as those in the flowchart of  FIG. 3  and thus, the description of S 41  to S 43  is not repeated herein for the sake of brevity. 
     The non-stationary rate calculation unit  16  determines whether the S 41  to S 43  processing on all the frames is finished (S 45 ). If the S 41  to S 43  processing on all the frames is not finished (NO in S 45 ), the non-stationary rate calculation unit  16  returns the method shown in  FIG. 6  to S 41  and allows the next frame to be subjected to the S 41  to S 43  processing. When the S 41  to S 43  processing on all the frames is finished (YES in S 45 ), the non-stationary rate calculation unit  16  allows the method to proceed to S 51  and S 52 . 
     S 51  and S 52  are the same as those in the flowchart of  FIG. 3  and thus, the description of S 51  to S 52  is not repeated herein for the sake of brevity. 
     The above-described first and third processes of setting a non-stationary determination threshold value may be combined. In addition, the above-described second and third processes of setting a non-stationary determination threshold value may be combined. 
     An operation of the above-described non-stationary rate calculation unit  16  is described in greater detail below. 
     Unvoiced segments include a long unvoiced segment (long segment) between sentences and a short unvoiced segment (short segment), such as, for example, the interval between breaths or an unvoiced plosive.  FIG. 7  is a waveform diagram illustrating long segments and short segments. When a frame determined as non-stationary is included in a long segment, a human auditory sense recognizes that the frame is the non-stationarity of a noise segment, namely, non-stationary noise is included in the noise segment. Whereas, when the frame determined as non-stationary is included in a short segment, the human auditory sense recognizes that the frame is the non-stationarity of a voiced segment, namely, non-stationary noise is included in the voiced segment. 
     To close the result of detection of non-stationarity to that obtained by the human auditory sense, the non-stationary rate calculation unit  16  may separate unvoiced segments into a long segment and a short segment to calculate non-stationary rates. In this case, the non-stationary rate calculation unit  16  determines, on the basis of the length of an unvoiced segment, whether the segment is a long segment or a short segment. The non-stationary rate calculation unit  16  calculates a non-stationary rate for each of the long and short segments. The non-stationary rate calculation unit  16  determines an unvoiced segment having a unvoiced segment threshold length or longer as a long segment and determines an unvoiced segment having a length shorter than the unvoiced segment threshold length as a short segment. 
     An operation of the above-described time change rate display unit  17  is described in greater detail below. 
       FIG. 8  is a waveform diagram illustrating spectrum time change rates displayed in time series. In  FIG. 8 , the axis of abscissa represents time. In the upper waveform W 1 , the axis of ordinate represents the amplitude of target data to be evaluated. In the lower waveform W 2 , the axis of ordinate represents the spectrum time change rate. The axis of abscissa common to the waveforms W 1  and W 2  represents time. The waveforms W 1  and W 2  are displayed in association with each other.  FIG. 8  further illustrates a non-stationary determination threshold value and three non-stationary frames in the waveform W 2 . As described above, each non-stationary frame is an unvoiced frame with a spectrum time change rate exceeding the non-stationary determination threshold value. 
     The time change rate display unit  17  may display the results of determination about stationary or non-stationary for each frame determined by the non-stationary rate calculation unit  16  in time series. For example, when a frame is determined as non-stationary, the frame is displayed as 1. When a frame is determined as stationary, the frame is displayed as 0. The time change rate display unit  17  may display these frames indicated by 1 and 0 in time series. 
     An operation of the above-described non-stationary rate display unit  18  is described in greater detail below. 
     As for the display form of an evaluation value displayed by the non-stationary rate display unit  18 , one evaluation value may be displayed for each target data to be evaluated. Alternatively, an evaluation value may be displayed for each of long and short segments. 
     The non-stationary rate display unit  18  may display a non-stationary rate itself as an evaluation value. Alternatively, the non-stationary rate display unit  18  may display a word indicating, for example, “GOOD”, “AVERAGE”, or “POOR”, the word being obtained by converting the non-stationary rate. In this case, one evaluation value may be assigned to each target data to be evaluated. Alternatively, an evaluation value may be assigned to each of long and short segments. 
     In the case where the non-stationary rate display unit  18  converts a non-stationary rate assigned to each of the long and short segments into a word, such as, for example, “GOOD”, “AVERAGE”, or “POOR”, making a reference of non-stationary rate conversion for a long segment different from that for a short segment is effective in agreeing with human auditory perception. As for a long segment, for example, when the non-stationary rate of a long segment is less than 1.0%, the non-stationary rate is converted into “GOOD”. When the non-stationary rate is equal to or greater than 1.0% and is less than 2.0%, the non-stationary rate is converted into “AVERAGE”. When the non-stationary rate is equal to or greater than 2.0%, the non-stationary rate is converted into “POOR”. As for a short segment, for example, when the non-stationary rate of a short segment is less than 4.0%, the non-stationary rate is converted into “GOOD”. When the non-stationary rate is equal to or greater than 4.0% and is less than 8.0%, the non-stationary rate is converted into “AVERAGE”. When the non-stationary rate is equal to or greater than 8.0%, the non-stationary rate is converted into “POOR”. 
     The speech signal evaluation apparatus  1  may use a power spectrum instead of the above-described amplitude spectrum. 
     According to the present embodiment, when the speech signal evaluation apparatus  1  performs speech signal processing, such as, for example, directional sound reception or nose reduction, on an original speech signal including various noises, the apparatus calculates the non-stationarity of an unvoiced segment on the basis of the spectrum time change rate of the unvoiced segment, thus evaluating the quality of the unvoiced segment. According to the present embodiment, the speech signal evaluation apparatus  1  may obtain an objective evaluation value as a quantitative evaluation value that matches subjective evaluation. According to the present embodiment, the speech signal evaluation apparatus  1  may quantify the quality of an unvoiced segment using only a speech signal with various noises subjected to speech signal processing without using original speech for comparison. 
     According to the present embodiment, the speech signal evaluation apparatus  1  calculates the rate of change of amplitude spectrum represented in a frequency domain, thus detecting the non-stationarity of an unvoiced segment. Consequently, the speech signal evaluation apparatus  1  may specify the position of a non-stationary noise, such as, for example, non-stationary noise of an unvoiced segment or musical noise generated by acoustical treatment, which a human being has known only when he or she actually listened speech subjected to speech signal processing. 
     The application of a speech signal evaluation method performed by the speech signal evaluation apparatus  1  according to the present embodiment is not limited to an evaluation test. The method may be used not only for the evaluation test but also for a tuning tool to increase the amount of reducing noise in speech signal processing or increase the quality of speech, a noise reduction apparatus for changing parameters while learning in real time, a noise environment measurement evaluation tool, a noise reduction apparatus for selecting an optimum noise reduction process on the basis of a result of noise environment measurement, and the like. 
     The present invention is applicable to a computer system which is described below.  FIG. 9  illustrates a computer system to which the embodiments described herein may be applied. Referring to  FIG. 9 , the computer system, indicated at  900 , includes a main body  901  which includes a central processing unit (CPU) and a disk drive, a display  902  which displays an image in accordance with an instruction from the main body  901 , a keyboard  903  for inputting various pieces of information to the computer system  900 , a mouse  904  which specifies any position on a display screen  902   a  of the display  902 , and a communication device  905  which accesses, for example, an external database to download, for instance, a program stored in another computer system. The communication device  905  may be, for example, a network communication card or a modem. 
     A program that allows a computer system constituting the above-described speech signal evaluation apparatus to execute the above-described processes or operations may be provided as a speech signal evaluation program. This program is stored into a recording medium that is readable by a computer system, so that the computer system constituting the speech signal evaluation apparatus can implement the program. The program that allows the execution of the above-described processes or operations is stored in a portable recording medium, such as a disk  910 , or is downloaded through the communication device  905  from a recording medium  906  of another computer system. The speech signal evaluation program that allows the computer system  900  to have at least a speech signal evaluation function is input to the computer system  900  and is compiled therein. This program allows the computer system  900  to operate as a speech signal evaluation system having the speech signal evaluation function. 
     This program may also be stored in a computer-readable recording medium, e.g., the disk  910 . Recording media readable by the computer system  900  include, for example, an internal storage device, such as a ROM or a RAM, installed in a computer, a portable storage medium, such as the disk  910 , a flexible disk, a digital versatile disk (DVD), a magneto-optical disk, or an IC card, a database holding a computer program, another computer system, a database thereof, and various recording media accessible through a computer system connected via communication means like the communication device  905 . 
     The main body  901  corresponds to the above-described CPU  801  and storage unit  802 . 
     A first detection unit corresponds to the segment determination unit  11  in the embodiment. A spectrum calculation unit corresponds to the FFT unit  13  and the amplitude spectrum calculation unit  14  in the embodiment. A variation calculation unit corresponds to the time change rate calculation unit  15  in the embodiment. A second detection unit corresponds to the non-stationary rate calculation unit  16  in the embodiment. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiment(s) of the present invention(s) has(have) been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.