Patent Publication Number: US-8977541-B2

Title: Speech processing apparatus, speech processing method and program

Description:
TECHNICAL FIELD 
     The present invention relates to a speech processing apparatus, a speech processing method and a program and, more particularly, relates to a speech processing apparatus, a speech processing method and a program which, when multichannel audio signals are downmixed and coded, prevent delay and an increase in the computation amount upon decoding of the audio signals. 
     BACKGROUND ART 
     A coding apparatus which codes multichannel audio signals can perform highly efficient coding by utilizing a relationship between channels. This coding includes, for example, intensity coding, M/S stereo coding and spatial coding. A coding apparatus which performs spatial coding downmixes an n channel audio signal into a m (m&lt;n) channel audio signal and codes the signal, finds spatial parameters representing the inter-channel relationship upon downmixing and transmits the spatial parameters together with the coded data. A decoding apparatus which receives the spatial parameters and the coded data decodes the coded data, and restores the original n channel audio signal from the m channel audio signal obtained as a result of decoding using the spatial parameter. 
     This spatial coding is known as “binaural cue coding”. For the spatial parameters (hereinafter, referred to as “BC parameters”), for example, ILD (Inter-channel Level Difference), IPD (Inter-channel Phase Difference) and ICC (Inter-channel Correlation) are used. The ILD refers to a parameter indicating the ratio of the magnitude of an inter-channel signal. The IPD refers to a parameter indicating an inter-channel phase difference, and the ICC refers to a parameter indicating an inter-channel correlation. 
       FIG. 1  is a block diagram illustrating a configuration example of a coding apparatus which performs spatial coding. 
     In addition, n=2 and m=1 for ease of description. That is, a coding target audio signal is a stereo audio signal (hereinafter, referred to as “stereo signal”), and coded data obtained as a result of coding is coded data of a monaural audio signal (hereinafter, referred to as “monaural signal”). 
     A coding apparatus  10  in  FIG. 1  includes a channel donwmix unit  11 , a spatial parameter detection unit  12 , an audio signal coding unit  13  and a multiplexing unit  14 . The coding apparatus  10  receives an input of a stereo signal including a left audio signal X L  and a right audio signal X R  as a coding target, and outputs coded data of a monaural signal. 
     More specifically, the channel downmix unit  11  of the coding apparatus  10  downmixes the stereo signal input as the coding target, to the monaural signal X M . Further, the channel downmix unit  11  supplies the monaural signal to the spatial parameter detection unit  12  and the audio signal coding unit  13 . 
     The spatial parameter detection unit  12  detects the BC parameters based on the monaural signal X M  supplied from the channel downmix unit  11  and the stereo signal input as the coding target, and supplies the BC parameters to the multiplexing unit  14 . 
     The audio signal coding unit  13  codes the monaural signal supplied from the channel downmix unit  11 , and supplies resulting coded data to the multiplexing unit  14 . 
     The multiplexing unit  14  multiplexes and outputs the coded data supplied from the audio signal coding unit  13  and the BC parameter supplied from the spatial parameter detection unit  12 . 
       FIG. 2  is a block diagram illustrating a configuration example of the audio signal coding unit  13  in  FIG. 1 . 
     In addition, the audio signal coding unit  13  in  FIG. 2  employs a configuration where the audio signal coding unit  13  performs coding according to, for example, MPEG-2 AAC LC (Moving Picture Experts Group phase 2 Advanced Audio Coding Low Complexity) profile. Meanwhile, the configuration is simplified and illustrated in  FIG. 2  for ease of description. 
     The audio signal coding unit  13  in  FIG. 2  includes a MDCT (Modified Discrete Cosine Transform) unit  21 , a spectrum quantization unit  22 , an entropy coding unit  23  and a multiplexing unit  24 . 
     The MDCT unit  21  performs MDCT of the monaural signal supplied from the channel downmix unit  11 , and transforms a monaural signal which is a time domain signal, into a MDCT coefficient which is a frequency domain coefficient. The MDCT unit  21  supplies the MDCT coefficient obtained as a result of transform, to the spectrum quantization unit  22  as a frequency spectrum coefficient. 
     The spectrum quantization unit  22  quantizes the frequency spectrum coefficient supplied from the MDCT unit  21 , and supplies the frequency spectrum coefficient to the entropy coding unit  23 . Further, the spectrum quantization unit  22  supplies quantization information which is information related to this quantization, to the multiplexing unit  24 . The quantization information includes, for example, a scale factor and quantization bit information. 
     The entropy coding unit  23  performs entropy coding such as Huffman coding or arithmetic coding of the quantized frequency spectrum coefficient supplied from the spectrum quantization unit  22 , and losslessly compresses the frequency spectrum coefficient. The entropy coding unit  23  supplies data obtained as a result of entropy coding, to the multiplexing unit  24 . 
     The multiplexing unit  24  multiplexes the data supplied from the entropy coding unit  23  and the quantization information supplied from the spectrum quantization unit  22 , and supplies resulting data to the multiplexing unit  14  ( FIG. 1 ) as coded data. 
       FIG. 3  is a block diagram illustrating another configuration example of the audio signal coding unit  13  in  FIG. 1 . 
     In addition, the audio signal coding unit  13  in  FIG. 3  employs a configuration of performing coding according to, for example, a MPEG-2 AAC SSR (Scalable Sample Rate) profile or MP3 (MPEG Audio Layer-3). Meanwhile, the configuration is simplified and illustrated in  FIG. 3  for ease of description. 
     The audio signal coding unit  13  in  FIG. 3  includes an analysis filter bank  31 , MDCT units  32 - 1  to  32 -N (N is an arbitrary integer), a spectrum quantization unit  33 , an entropy coding unit  34  and a multiplexing unit  35 . 
     The analysis filter bank  31  includes, for example, a QMF (Quadrature Mirror Filterbank) bank or a PQF (Poly-phase Quadrature Filter) bank. The analysis filter bank  31  divides the monaural signal supplied from the channel downmix unit  11 , into N groups according to a frequency. The analysis filter bank  31  supplies N subband signals obtained as a result of division, to the MDCT units  32 - 1  to  32 -N. 
     The MDCT units  32 - 1  to  32 -N each perform MDCT of the subband signal supplied from the analysis filter bank  31 , and transforms the subband signal which is a time domain signal, into a MDCT coefficient which is a frequency domain coefficient. Further, the MDCT units  32 - 1  to  32 -N each supply the MDCT coefficient of each subband signal to the spectrum quantization unit  33  as the frequency spectrum coefficient. 
     The spectrum quantization unit  33  quantizes each of the N frequency spectrum coefficients supplied from the MDCT units  32 - 1  to  32 -N, and supplies the N frequency spectrum coefficients to the entropy coding unit  34 . Further, the spectrum quantization unit  33  supplies quantization information about this quantization, to the multiplexing unit  35 . 
     The entropy coding unit  34  performs entropy coding such as Huffman coding or arithmetic coding of each of the quantized N frequency spectrum coefficients supplied from the spectrum quantization unit  33 , and losslessly compresses the N frequency spectrum coefficients. The entropy coding unit  34  supplies N items of data obtained as a result of entropy coding, to the multiplexing unit  35 . 
     The multiplexing unit  35  multiplexes the N items of data supplied from the entropy coding unit  34  and the quantization information supplied from the spectrum quantization unit  33 , and supplies resulting data to the multiplexing unit  14  ( FIG. 1 ) as coded data. 
       FIG. 4  is a block diagram illustrating a configuration example of a decoding apparatus which decodes coded data which is spatially coded by the coding apparatus  10  in  FIG. 1 . 
     A decoding apparatus  40  in  FIG. 4  includes an inverse multiplexing unit  41 , an audio signal decoding unit  42 , a generation parameter calculation unit  43  and a stereo signal generation unit  44 . The decoding apparatus  40  decodes the coded data supplied from the coding apparatus in  FIG. 1 , and generates a stereo signal. 
     More specifically, the inverse multiplexing unit  41  of the decoding apparatus  40  inversely multiplexes the multiplexed coded data supplied from the coding apparatus  10  in  FIG. 1 , and obtains the coded data and the BC parameter. The inverse multiplexing unit  41  supplies the coded data to the audio signal decoding unit  42 , and supplies the BC parameter to the generation parameter calculation unit  43 . 
     The audio signal decoding unit  42  decodes the coded data supplied from the inverse multiplexing unit  41 , and supplies the resulting monaural signal X M  which is a time domain signal, to the stereo signal generation unit  44 . 
     The generation parameter calculation unit  43  calculates generation parameters which are parameters for generating a stereo signal from a monaural signal which is a decoding result of the multiplexed coded data, using the BC parameter supplied from the inverse multiplexing unit  41 . The generation parameter calculation unit  43  supplies these generation parameters to the stereo signal generation unit  44 . 
     The stereo signal generation unit  44  generates the left audio signal X L  and the right audio signal X R  from the monaural signal X M  supplied from the audio signal decoding unit  42  using the generation parameters supplied from the generation parameter calculation unit  43 . The stereo signal generation unit  44  outputs the left audio signal X L  and the right audio signal X R  as stereo signals. 
       FIG. 5  is a block diagram illustrating a configuration example of the audio signal decoding unit  42  in  FIG. 4 . 
     In addition, the audio signal decoding unit  42  in  FIG. 5  employs a configuration where coded data coded according to, for example, the MPEG-2 AAC LC profile is input to the decoding apparatus  40 . That is, the audio signal decoding unit  42  in  FIG. 5  decodes the coded data coded by the audio signal coding unit  13  in  FIG. 2 . 
     The audio signal decoding unit  42  in  FIG. 5  includes an inverse multiplexing unit  51 , an entropy decoding unit  52 , a spectrum inverse quantization unit  53  and an IMDCT unit  54 . 
     The inverse multiplexing unit  51  inversely multiplexes the coded data supplied from the inverse multiplexing unit  41  in  FIG. 4 , and obtains the quantized and entropy-coded frequency spectrum coefficient and the quantization information. The inverse multiplexing unit  51  supplies the quantized and entropy-coded frequency spectrum coefficient to the entropy decoding unit  52 , and supplies the quantization information to the spectrum inverse quantization unit  53 . 
     The entropy decoding unit  52  performs entropy decoding such as Huffman decoding or arithmetic decoding of the frequency spectrum coefficient supplied from the inverse multiplexing unit  51 , and restores the quantized frequency spectrum coefficient. The entropy decoding unit  52  supplies this frequency spectrum coefficient to the spectrum inverse quantization unit  53 . 
     The spectrum inverse quantization unit  53  inversely quantizes the quantized frequency spectrum coefficient supplied from the entropy decoding unit  52  based on the quantization information supplied from the inverse multiplexing unit  51 , and restores the frequency spectrum coefficient. Further, the spectrum inverse quantization unit  53  supplies the frequency spectrum coefficient to the IMDCT (Inverse MDCT) (Inverse Modified Discrete Cosine Transform) unit  54 . 
     The IMDCT unit  54  performs IMDCT of the frequency spectrum coefficient supplied from the spectrum inverse quantization unit  53 , and transforms the frequency spectrum coefficient into the monaural signal X M  which is a time domain signal. The IMDCT unit  54  supplies this monaural signal X M  to the stereo signal generation unit  44  ( FIG. 4 ). 
       FIG. 6  is a block diagram illustrating another configuration example of the audio signal decoding unit  42  in  FIG. 4 . 
     In addition, the audio signal decoding unit  42  in  FIG. 6  employs a configuration where coded data coded according to, for example, the MPEG-2 AAC SSR profile or a method such as MP3 is input to the decoding apparatus  40 . That is, the audio signal decoding unit  42  in  FIG. 6  decodes the coded data coded by the audio signal coding unit  13  in  FIG. 3 . 
     The audio signal decoding unit  42  in  FIG. 6  includes an inverse multiplexing unit  61 , an entropy decoding unit  62 , a spectrum inverse quantization unit  63 , IMDCT units  64 - 1  to  64 -N and a synthesis filter bank  65 . 
     The inverse multiplexing unit  61  inversely multiplexes the coded data supplied from the inverse multiplexing unit  41  in  FIG. 4 , and obtains the quantized and entropy-coded frequency spectrum coefficients of the N subband signals and the quantization information. The inverse multiplexing unit  61  supplies the quantized and entropy-coded frequency spectrum coefficients of the N subband signals to the entropy decoding unit  62 , and supplies the quantization information to the spectrum inverse quantization unit  63 . 
     The entropy decoding unit  62  performs entropy decoding such Huffman decoding or arithmetic decoding of the frequency spectrum coefficients of the N subband signals supplied from the inverse multiplexing unit  61 , and supplies the frequency spectrum coefficients to the spectrum inverse quantization unit  63 . 
     The spectrum inverse quantization unit  63  inversely quantizes each of the frequency spectrum coefficients of the N subband signals which are supplied from the entropy decoding unit  62  and which are obtained as a result of entropy decoding, based on the quantization information supplied from the inverse multiplexing unit  61 . By this means, the frequency spectrum coefficients of the N subband signals are restored. The spectrum inverse quantization unit  63  supplies the restored frequency spectrum coefficients of the N subband signals to the IMDCT units  64 - 1  to  64 -N one by one. 
     The IMDCT units  64 - 1  to  64 -N each perform IMDCT of the frequency spectrum coefficient supplied from the spectrum inverse quantization unit  63 , and transform the frequency spectrum coefficient into a subband signal which is a time domain signal. The IMDCT units  64 - 1  to  64 -N each supply the subband signal obtained as a result of transform, to the synthesis filter bank  65 . 
     The synthesis filter bank  65  includes, for example, an inverse PQF and an inverse QMF. The synthesis bank  65  synthesizes the N subband signals supplied from the IMDCT units  64 - 1  to  64 -N, and supplies the resulting signal to the stereo signal generation unit  44  ( FIG. 4 ) as the monaural signal X M . 
       FIG. 7  is a block diagram illustrating a configuration example of the stereo signal generation unit  44  in  FIG. 4 . 
     The stereo signal generation unit  44  in  FIG. 7  includes a reverb signal generation unit  71  and a stereo synthesis unit  72 . 
     The reverb signal generation unit  71  generates a signal X D  which is uncorrelated with this monaural signal X M  using the monaural signal X M  supplied from the audio signal decoding unit  42  in  FIG. 4 . For the reverb signal generation unit  71 , a comb filter or an all pass filter is generally used. In this case, the reverb signal generation unit  71  generates a reverb signal of the monaural signal X M  as the signal X D . 
     In addition, for the reverb signal generation unit  71 , a feedback delay network (FDN) is used in some cases (see, for example, Patent Document 1). 
     The reverb signal generation unit  71  supplies the generated signal X D  to the stereo synthesis unit  72 . 
     The stereo synthesis unit  72  synthesizes the monaural signal X M  supplied from the audio signal decoding unit  42  in  FIG. 4  and the signal X D  supplied from the reverb signal generation unit  71  using the generation parameters supplied from the generation parameter calculation unit  43  in  FIG. 4 . Further, the stereo synthesis unit  72  outputs the left audio signal X L  and the right audio signal X R  obtained as a result of synthesis as stereo signals. 
       FIG. 8  is a block diagram illustrating another configuration example of the stereo signal generation unit  44  in  FIG. 4 . 
     The stereo signal generation unit  44  in  FIG. 8  includes an analysis filter bank  81 , subband stereo signal generation units  82 - 1  to  82 -P (P is an arbitrary number) and a synthesis filter bank  83 . 
     In addition, when the stereo signal generation unit  44  in  FIG. 4  employs the configuration illustrated in  FIG. 8 , the spatial parameter detection unit  12  of the coding apparatus  10  in  FIG. 1  detects the BC parameter per subband signal. 
     More specifically, for example, the spatial parameter detection unit  12  has two analysis filter banks. Further, in the spatial parameter detection unit  12 , one analysis filter bank divides the stereo signal according to a frequency, and the other analysis filter bank divides the monaural signal from the channel downmix unit  11  according to a frequency. The spatial parameter detection unit  12  detects the BC parameter per subband signal based on the subband signal of the stereo signal and the subband signal of the monaural signal obtained as a result of division. Further, the generation parameter calculation unit  43  in  FIG. 4  receives a supply of the BC parameter of each subband signal from the inverse multiplexing unit  41 , and generates generation parameters per subband signal. 
     The analysis filter bank  81  includes, for example, a QMF (Quadrature Mirror Filter) bank. The analysis filter bank  81  divides the monaural signal X M  supplied from the audio signal decoding unit  42  in  FIG. 4  into P groups according to a frequency. The analysis filter bank  81  supplies P subband signals obtained as a result of division, to the subband stereo signal generation units  82 - 1  to  82 -P. 
     The subband stereo signal generation units  82 - 1  to  82 -P each include a reverb signal generation unit and a stereo synthesis unit. The configuration of each of the subband stereo signal generation units  82 - 1  to  82 -P is the same, and therefore only the subband stereo signal generation unit  82 -B will be described. 
     The subband stereo signal generation unit  82 -B includes a reverb signal generation unit  91  and a stereo synthesis unit  92 . The reverb signal generation unit  91  generates a signal X D   B  which is irrelevant to this subband signal X m   B  using the subband signal X m   B  of the monaural signal supplied from the analysis filter bank  81 , and supplies the signal X D   B  to the stereo synthesis unit  92 . 
     The stereo synthesis unit  92  synthesizes the subband signal X m   B  supplied from the analysis filter bank  81  and the signal X D   B  supplied from the reverb signal generation unit  91  using the generation parameters of the subband signal X m   B  supplied from the generation parameter calculation unit  43  in  FIG. 4 . Further, the stereo synthesis unit  92  supplies the left audio signal X L   B  and the right audio signal X R   B  obtained as a result of synthesis, to the synthesis filter bank  83  as subband signals of the stereo signals. 
     The synthesis filter bank  83  synthesizes left and right stereo signals of each subband signal supplied from the subband stereo signal generation units  82 - 1  to  82 -P at a time. The synthesis filter bank  83  outputs the resulting left audio signal X L  and right audio signal X R  as stereo signals. 
     In addition, the configuration of the stereo signal generation unit  44  in  FIG. 8  is disclosed, in for example, Patent Document 2. 
     Further, a coding apparatus which performs intensity coding mixes the frequency spectrum coefficient of each channel at a frequency equal to or more than a predetermined frequency band of the input stereo signal, and generates the frequency spectrum coefficient of the monaural signal. Further, the coding apparatus outputs a level ratio of the frequency spectrum coefficient of this monaural signal and an inter-channel frequency spectrum coefficient as a coding result. 
     More specifically, the coding apparatus which performs intensity coding performs MDCT with respect to the stereo signal, and mixes and shares the frequency spectrum coefficient of each channel at a frequency equal to or more than a predetermined frequency band among resulting frequency spectrum coefficients of channels. Further, the coding apparatus which performs intensity coding quantizes and entropy-codes the shared frequency spectrum coefficient, and multiplexes resulting data and quantization information as coded data. Furthermore, the coding apparatus which performs intensity coding finds the level ratio of the inter-channel frequency spectrum coefficients, and multiplexes and outputs the level ratio and the coded data. 
     Still further, a decoding apparatus which performs intensity decoding inversely multiplexes the coded data on which the level ratio of the inter-channel frequency spectrum coefficients is multiplexed, entropy-decodes resulting coded data and inversely quantizes the coded data based on the quantization information. Moreover, the decoding apparatus which performs intensity decoding restores the frequency spectrum coefficient of each channel based on the level ratio of the frequency spectrum coefficient obtained as a result of inverse quantization and the inter-channel frequency spectrum coefficients multiplexed on the coded data. Moreover, the decoding apparatus which performs intensity decoding performs IMDCT of the restored frequency spectrum coefficient of each channel, and obtains a stereo signal at a frequency equal to or more than a predetermined frequency band. 
     Although such intensity coding ratio is usually used to improve a coding efficiency, a high band frequency spectrum coefficient of a stereo signal is monaural-coded and represented only by an inter-channel level difference, and therefore the original stereophonic effect is slightly lost. 
     CITATION LIST 
     Patent Documents 
     
         
         Patent Document 1: Japanese Patent Application Laid-Open No. 2006-325162 
         Patent Document 2: Japanese Patent Application Laid-Open No. 2006-524832 
       
    
     SUMMARY OF THE INVENTION 
     Problems to Be Solved By the Invention 
     As described above, the decoding apparatus  40  which decodes conventional spatially coded data generates the signal X D  and signals X D   1  to X D   P  which are irrelevant to the monaural signal X M  used upon generation of a stereo signal, using the monaural signal X M  which is a time domain signal. 
     Therefore, the reverb signal generation unit  71  which generates the signal X D , and the analysis filter bank  81  and the reverb signal generation units  91  of the subband stereo signal generation units  82 - 1  to  82 -P which generate the signals X D   1  to X D   P  cause delay, and increases algorithm delay of the decoding apparatus  40 . This causes a problem when, for example, the decoding apparatus  40  is requested to provide immediate response performance or the decoding apparatus  40  is used in real-time communication, that is, when low delay property is important. 
     Further, filter computation in the reverb signal generation unit  71 , and the analysis filter bank  81  and the reverb signal generation units  91  of the subband stereo signal generation units  82 - 1  to  82 -P increases the computation amount, and also increases the required buffer capacity. 
     In light of such a situation, the present invention can prevent delay and an increase in the computation amount upon decoding of audio signals when multichannel audio signals are downmixed and coded. 
     Solutions to Problems 
     A speech processing apparatus according to an aspect of the present invention includes: an acquisition unit which acquires frequency domain coefficients of speech signals of channels which are generated from speech signals which are speech time domain signals of a plurality of channels, and the number of which is less than a plurality of channels, and a parameter representing a relationship between the plurality of channels; a first transform unit which transforms the frequency domain coefficients acquired by the acquisition unit, into first time domain signals; a second transform unit which transforms the frequency domain coefficients acquired by the acquisition unit, into second time domain signals; and a synthesis unit which generates the speech signals of the plurality of channels by synthesizing the first time domain signals and the second time domain signals using the parameter, wherein a base of transform performed by the first transform unit and a base of transform performed by the second transform unit are orthogonal. 
     A speech processing method and a program according to an aspect of the present invention support a speech processing apparatus according to an aspect of the present invention. 
     According to an aspect of the present invention, frequency domain coefficients of speech signals of channels which are generated from speech signals which are speech time domain signals of a plurality of channels, and the number of which is less than a plurality of channels, and a parameter representing a relationship between the plurality of channels are acquired, the acquired frequency domain coefficients are transformed into first time domain signals, the acquired frequency domain coefficients are transformed into second time domain signals, and the speech signals of the plurality of channels are generated by synthesizing the first time domain signals and the second time domain signals using the parameter. In addition, a base of transform into the first time domain signals and a base of transform into the second time domain signals are orthogonal. 
     The speech processing apparatus according to an aspect of the present invention may be an independent apparatus or may be an internal block which forms one apparatus. 
     Effects of the Invention 
     According to an aspect of the present invention, it is possible to prevent delay and an increase in the computation amount upon decoding of audio signals when multichannel audio signals are downmixed and coded. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram illustrating a configuration example of a coding apparatus which performs spatial coding. 
         FIG. 2  is a block diagram illustrating a configuration example of an audio signal coding unit in  FIG. 1 . 
         FIG. 3  is a block diagram illustrating another configuration example of the audio signal coding unit in  FIG. 1 . 
         FIG. 4  is a block diagram illustrating a configuration example of a decoding apparatus which decodes spatially coded data. 
         FIG. 5  is a block diagram illustrating a configuration example of an audio signal decoding unit in  FIG. 4 . 
         FIG. 6  is a block diagram illustrating another configuration example of the audio signal decoding unit in  FIG. 4 . 
         FIG. 7  is a block diagram illustrating a configuration example of a stereo signal generation unit in  FIG. 4 . 
         FIG. 8  is a block diagram illustrating another configuration example of the stereo signal generation unit in  FIG. 4 . 
         FIG. 9  is a block diagram illustrating a configuration example of a speech processing apparatus to which the present invention is applied according to a first embodiment. 
         FIG. 10  is a block diagram illustrating a detailed configuration example of an uncorrelated frequency-time transform unit in  FIG. 9 . 
         FIG. 11  is a block diagram illustrating another detailed configuration example of the uncorrelated frequency-time transform unit in  FIG. 9 . 
         FIG. 12  is a block diagram illustrating a detailed configuration example of a stereo synthesis unit in  FIG. 9 . 
         FIG. 13  illustrates a view illustrates a vector of each signal. 
         FIG. 14  is a flowchart for describing decoding processing of the speech processing apparatus in  FIG. 9 . 
         FIG. 15  is a block diagram illustrating a configuration example of a speech processing apparatus to which the present invention is applied according to a second embodiment. 
         FIG. 16  is a flowchart for describing decoding processing of the speech processing apparatus in  FIG. 15 . 
         FIG. 17  is a block diagram illustrating a configuration example of a speech processing apparatus to which the present invention is applied according to a third embodiment. 
         FIG. 18  is a flowchart for describing decoding processing of the speech processing apparatus in  FIG. 17 . 
         FIG. 19  is a block diagram illustrating a configuration example of a speech processing apparatus to which the present invention is applied according to a fourth embodiment. 
         FIG. 20  is a flowchart for describing decoding processing of the speech processing apparatus in  FIG. 19 . 
         FIG. 21  is a view illustrating a configuration example of a computer according to an embodiment. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     First Embodiment 
     Configuration Example of Speech Processing Apparatus According to First Embodiment 
       FIG. 9  is a block diagram illustrating a configuration example of a speech processing apparatus to which the present invention is applied according to a first embodiment. 
     The same configuration illustrated in  FIG. 9  as configurations illustrated in  FIGS. 4 and 5  will be assigned the same reference numerals. Overlapping description will be adequately skipped. 
     The configuration of the speech processing apparatus  100  in  FIG. 9  differs from the configuration of a decoding apparatus  40  in  FIG. 4  which has an audio signal decoding unit  42  in  FIG. 5  and a stereo signal generation unit  44  in  FIG. 7  mainly in that an inverse multiplexing unit  101  is provided instead of an inverse multiplexing unit  41  and an inverse multiplexing unit  51 , an uncorrelated frequency-time transform unit  102  is provided instead of an IMDCT unit  54  and a reverb signal generation unit  71 , and a stereo synthesis unit  103  and a generation parameter calculation unit  104  are provided instead of a stereo synthesis unit  72  and a generation parameter calculation unit  43 . 
     The speech processing apparatus  100  decodes, for example, coded data spatially coded by a coding apparatus  10  in  FIG. 1  which has an audio signal coding unit  13  in  FIG. 2 . In this case, the speech processing apparatus  100  generates a signal X D ′ which is irrelevant to a monaural signal X M  used upon generation of a stereo signal, using a frequency spectrum coefficient of the monaural signal X M . 
     More specifically, the inverse multiplexing unit  101  (acquisition unit) of the speech processing apparatus  100  corresponds to the inverse multiplexing unit  41  in  FIG. 4  and the inverse multiplexing unit  51  in  FIG. 5 . That is, the inverse multiplexing unit  101  inversely multiplexes multiplexed coded data supplied from the coding apparatus  10  in  FIG. 1 , and acquires the coded data and a BC parameter. In addition, although the BC parameter multiplexed on the coded data may be a BC parameter of all frames or may be a BC parameter of a predetermined frame, the BC parameter here refers to the BC parameter of a predetermined frame. 
     Further, the inverse multiplexing unit  101  inversely multiplexes the coded data, and obtains a quantized and entropy-coded frequency spectrum coefficient and quantization information. Furthermore, the inverse multiplexing unit  101  supplies the quantized and entropy-coded frequency spectrum coefficient, to the entropy decoding unit  52 , and supplies the quantization information to the spectrum inverse quantization unit  53 . Still further, the inverse multiplexing unit  101  supplies the BC parameter to the generation parameter calculation unit  104 . 
     The uncorrelated frequency-time transform unit  102  generates the monaural signal X M  and the signal X D ′ which are two uncorrelated time domain signals, from the frequency spectrum coefficient of the monaural signal X M  obtained as a result of inverse quantization by the spectrum inverse quantization unit  53 . Further, the uncorrelated frequency-time transform unit  102  supplies the monaural signal X M  and the signal X D ′ to the stereo synthesis unit  103 . This uncorrelated frequency-time transform unit  102  will be described in detail with reference to  FIGS. 10 and 11  which will be described below. 
     The stereo synthesis unit  103  (synthesis unit) synthesizes the monaural signal X M  and the signal X D ′ supplied from the uncorrelated frequency-time transform unit  102 , using generation parameters supplied from the generation parameter calculation unit  104 . Further, the stereo synthesis unit  103  outputs a left audio signal X L  and a right audio signal X R  obtained as a result of synthesis as stereo signals. This stereo synthesis unit  103  will be described in detail with reference to  FIG. 12  which will be described below. 
     The generation parameter calculation unit  104  interpolates the BC parameter of a predetermined frame supplied from the inverse multiplexing unit  101 , and calculates the BC parameter of each frame. The generation parameter calculation unit  104  generates the generation parameters using the BC parameter of a current processing target frame, and supplies the generation parameters to the stereo synthesis unit  103 . 
     [Detailed Configuration Example of Uncorrelated Frequency-Time Transform Unit] 
       FIG. 10  is a block diagram illustrating a detailed configuration example of an uncorrelated frequency-time transform unit  102  in  FIG. 9 . 
     The uncorrelated frequency-time transform unit  102  in  FIG. 10  includes an IMDCT unit  54  and an IMDST unit  111 . 
     The IMDCT unit  54  (first transform unit) in  FIG. 10  is the same as the IMDCT unit  54  in  FIG. 5 , and performs IMDCT of the frequency spectrum coefficient of the monaural signal X M  supplied from the spectrum inverse quantization unit  53 . Further, the IMDCT unit  54  supplies the resulting monaural signal X M  which is a time domain signal (first time domain signal) to the stereo synthesis unit  103  ( FIG. 9 ). 
     The IMDST (Inverse Modified Discrete Sine Transform) unit  111  (second transform unit) performs IMDST of the frequency spectrum coefficient of the monaural signal X M  supplied from the vector inverse quantization unit  53 . Further, the IMDST unit  111  supplies the resulting signal X D ′ which is a time domain signal (second time domain signal) to the stereo synthesis unit  103  ( FIG. 9 ). 
     As described above, transform performed by the IMDCT unit  54  is inverse cosine transform and transform performed by the IMDST unit  111  is inverse sine transform, and the base of transform performed by the IMDCT unit  54  and the base of transform performed by the IMDST unit  111  are orthogonal. Consequently, it is possible to regard that the monaural signal X M  and the signal X D ′ are substantially uncorrelated to each other. 
     In addition, MDCT, IMDCT and IMDST are defined according to following equations (1) to (3). 
     
       
         
           
             
               
                 
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                             ) 
                           
                         
                         · 
                         
                           cos 
                           ⁡ 
                           
                             [ 
                             
                               
                                 π 
                                 
                                   4 
                                   ⁢ 
                                   N 
                                 
                               
                               ⁢ 
                               
                                 ( 
                                 
                                   
                                     2 
                                     ⁢ 
                                     n 
                                   
                                   + 
                                   1 
                                   + 
                                   N 
                                 
                                 ) 
                               
                               ⁢ 
                               
                                 ( 
                                 
                                   
                                     2 
                                     ⁢ 
                                     k 
                                   
                                   + 
                                   1 
                                 
                                 ) 
                               
                             
                             ] 
                           
                         
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       k 
                       = 
                       0 
                     
                     , 
                     1 
                     , 
                     … 
                     ⁢ 
                     
                         
                     
                     , 
                     
                       N 
                       - 
                       1 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
             
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       y 
                       ⁡ 
                       
                         ( 
                         n 
                         ) 
                       
                     
                     = 
                     
                       
                         
                           2 
                           · 
                           
                             
                               w 
                               ′ 
                             
                             ⁡ 
                             
                               ( 
                               n 
                               ) 
                             
                           
                         
                         N 
                       
                       · 
                       
                         
                           ∑ 
                           
                             k 
                             = 
                             0 
                           
                           
                             N 
                             - 
                             1 
                           
                         
                         ⁢ 
                         
                           
                             Xc 
                             ⁡ 
                             
                               ( 
                               k 
                               ) 
                             
                           
                           · 
                           
                             cos 
                             ⁡ 
                             
                               [ 
                               
                                 
                                   π 
                                   
                                     4 
                                     ⁢ 
                                     N 
                                   
                                 
                                 ⁢ 
                                 
                                   ( 
                                   
                                     
                                       2 
                                       ⁢ 
                                       n 
                                     
                                     + 
                                     1 
                                     + 
                                     N 
                                   
                                   ) 
                                 
                                 ⁢ 
                                 
                                   ( 
                                   
                                     
                                       2 
                                       ⁢ 
                                       k 
                                     
                                     + 
                                     1 
                                   
                                   ) 
                                 
                               
                               ] 
                             
                           
                         
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       n 
                       = 
                       0 
                     
                     , 
                     1 
                     , 
                     … 
                     ⁢ 
                     
                         
                     
                     , 
                     
                       
                         2 
                         ⁢ 
                         N 
                       
                       - 
                       1 
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
             
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     3 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       y 
                       ⁡ 
                       
                         ( 
                         n 
                         ) 
                       
                     
                     = 
                     
                       
                         
                           2 
                           · 
                           
                             
                               w 
                               ′ 
                             
                             ⁡ 
                             
                               ( 
                               n 
                               ) 
                             
                           
                         
                         N 
                       
                       · 
                       
                         
                           ∑ 
                           
                             k 
                             = 
                             0 
                           
                           
                             N 
                             - 
                             1 
                           
                         
                         ⁢ 
                         
                           
                             Xs 
                             ⁡ 
                             
                               ( 
                               k 
                               ) 
                             
                           
                           · 
                           
                             sin 
                             ⁡ 
                             
                               [ 
                               
                                 
                                   π 
                                   
                                     4 
                                     ⁢ 
                                     N 
                                   
                                 
                                 ⁢ 
                                 
                                   ( 
                                   
                                     
                                       2 
                                       ⁢ 
                                       n 
                                     
                                     + 
                                     1 
                                     + 
                                     N 
                                   
                                   ) 
                                 
                                 ⁢ 
                                 
                                   ( 
                                   
                                     
                                       2 
                                       ⁢ 
                                       k 
                                     
                                     + 
                                     1 
                                   
                                   ) 
                                 
                               
                               ] 
                             
                           
                         
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       n 
                       = 
                       0 
                     
                     , 
                     1 
                     , 
                     … 
                     ⁢ 
                     
                         
                     
                     , 
                     
                       
                         2 
                         ⁢ 
                         N 
                       
                       - 
                       1 
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     In equations (1) to (3), x(n) is a time domain signal, w(n) is a transform window, w′ (n) is an inverse transform window and y(n) is an inversely transformed signal. Further, Xc(k) is a MDCT coefficient, and Xs(k) is a MDST coefficient. 
     [Detailed Configuration Example of Uncorrelated Frequency-Time Transform Unit] 
       FIG. 11  is a block diagram illustrating another detailed configuration example of the uncorrelated frequency-time transform unit  102  in  FIG. 9 . 
     The same configuration illustrated in  FIG. 11  as the configuration in  FIG. 10  will be assigned same reference numerals. Overlapping description will be adequately skipped. 
     The configuration of the uncorrelated frequency-time transform unit  102  in  FIG. 11  differs from the configuration in  FIG. 10  mainly in that a spectrum inversion unit  121 , an IMDCT unit  122  and a sign inversion unit  123  are provided instead of the IMDST unit  111 . 
     The spectrum inversion unit  121  of the uncorrelated frequency-time transform unit  102  in  FIG. 11  inverts the frequency spectrum coefficient supplied from the spectrum inverse quantization unit  53  such that frequencies are in an inverse order, and supplies the frequency spectrum coefficients to the IMDCT unit  122 . 
     The IMDCT unit  122  performs IMDCT of the frequency spectrum coefficients supplied from the spectrum inversion unit  121 , and obtains time domain signals. The IMDCT unit  122  supplies these time domain signals to the sign inversion unit  123 . 
     The sign inversion unit  123  inverts the sign of an odd sample of the time domain signal supplied from the IMDCT unit  122 , and obtains the signal X D ′. 
     Meanwhile, when Xs(k) is replaced with Xs(N−k−1) in above equation 3 which defines IMDST, if N is a common multiple of 4, equation 3 can be modified to following equation 4. 
     
       
         
           
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     [ 
                     
                       Equation 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       4 
                     
                     ] 
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     y 
                     ⁡ 
                     
                       ( 
                       n 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         
                           2 
                           · 
                           
                             
                               w 
                               ′ 
                             
                             ⁡ 
                             
                               ( 
                               n 
                               ) 
                             
                           
                         
                         N 
                       
                       · 
                       
                         
                           ∑ 
                           
                             k 
                             = 
                             0 
                           
                           
                             N 
                             - 
                             1 
                           
                         
                         ⁢ 
                         
                           
                             Xs 
                             ⁡ 
                             
                               ( 
                               
                                 N 
                                 - 
                                 k 
                                 - 
                                 1 
                               
                               ) 
                             
                           
                           · 
                           
                             sin 
                             ⁡ 
                             
                               [ 
                               
                                 
                                   π 
                                   
                                     4 
                                     ⁢ 
                                     N 
                                   
                                 
                                 ⁢ 
                                 
                                   ( 
                                   
                                     
                                       2 
                                       ⁢ 
                                       n 
                                     
                                     + 
                                     1 
                                     + 
                                     N 
                                   
                                   ) 
                                 
                                 ⁢ 
                                 
                                   ( 
                                   
                                     
                                       2 
                                       ⁢ 
                                       
                                         ( 
                                         
                                           N 
                                           - 
                                           k 
                                           - 
                                           1 
                                         
                                         ) 
                                       
                                     
                                     + 
                                     1 
                                   
                                   ) 
                                 
                               
                               ] 
                             
                           
                         
                       
                     
                     = 
                     
                       
                         
                           
                             2 
                             · 
                             
                               
                                 w 
                                 ′ 
                               
                               ⁡ 
                               
                                 ( 
                                 n 
                                 ) 
                               
                             
                           
                           N 
                         
                         · 
                         
                           
                             ( 
                             
                               - 
                               1 
                             
                             ) 
                           
                           n 
                         
                         · 
                         
                           
                             ∑ 
                             
                               k 
                               = 
                               0 
                             
                             
                               N 
                               - 
                               1 
                             
                           
                           ⁢ 
                           
                             
                               Xs 
                               ⁡ 
                               
                                 ( 
                                 
                                   N 
                                   - 
                                   k 
                                   - 
                                   1 
                                 
                                 ) 
                               
                             
                             · 
                             
                               cos 
                               ⁡ 
                               
                                 [ 
                                 
                                   
                                     π 
                                     
                                       4 
                                       ⁢ 
                                       N 
                                     
                                   
                                   ⁢ 
                                   
                                     ( 
                                     
                                       
                                         2 
                                         ⁢ 
                                         n 
                                       
                                       + 
                                       1 
                                       + 
                                       N 
                                     
                                     ) 
                                   
                                   ⁢ 
                                   
                                     ( 
                                     
                                       
                                         2 
                                         ⁢ 
                                         k 
                                       
                                       + 
                                       1 
                                     
                                     ) 
                                   
                                 
                                 ] 
                               
                             
                           
                         
                       
                       = 
                       
                         
                           
                             ( 
                             
                               - 
                               1 
                             
                             ) 
                           
                           n 
                         
                         · 
                         
                           IMDCT 
                           ⁡ 
                           
                             [ 
                             
                               Xs 
                               ⁡ 
                               
                                 ( 
                                 
                                   N 
                                   - 
                                   k 
                                   - 
                                   1 
                                 
                                 ) 
                               
                             
                             ] 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     Hence, a signal obtained as a result of performing IMDST of the frequency spectrum coefficients from the spectrum inverse quantization unit  53 , and a signal obtained as a result of inverting and performing IMDST of the frequency spectrum coefficients such that the frequencies are in an inverse order and inverting the sign of the odd sample are the same signal X D ′. That is, the IMDST unit  111  in  FIG. 10 , and the spectrum inversion unit  121 , the IMDCT unit  122  and the sign inversion unit  123  in  FIG. 11  are equivalent. 
     The sign inversion unit  123  supplies the obtained signal X D ′ to the stereo synthesis unit  103  in  FIG. 9 . 
     As described above, the uncorrelated frequency-time transform unit  102  in  FIG. 11  only needs to be provided with an IMDCT unit alone in order to transform a time domain signal into a frequency spectrum coefficient, so that it is possible to reduce manufacturing cost compared to a case where the IMDCT unit and the IMDST unit in  FIG. 9  need to be provided. 
     [Detailed Configuration Example of Stereo Synthesis Unit] 
       FIG. 12  is a block diagram illustrating a detailed configuration example of the stereo synthesis unit  103  in FIG.  9 . 
     The stereo synthesis unit  103  in  FIG. 12  includes multipliers  141  to  144 , and an adder  145  and an adder  146 . 
     The multiplier  141  multiplies the monaural signal X M  supplied from the uncorrelated frequency-time transform unit  102 , with a coefficient h 11  which is one of generation parameters supplied from the generation parameter calculation unit  104 . The multiplier  141  supplies a resulting multiplication value h 11 ×X M  to the adder  145 . 
     The multiplier  142  multiplies the monaural signal X M  supplied from the uncorrelated frequency-time transform unit  102 , with a coefficient h 21  which is one of generation parameters supplied from the generation parameter calculation unit  104 . The multiplier  141  supplies a resulting multiplication value h 21 ×X M  to the adder  146 . 
     The multiplier  143  multiplies the signal X D ′ supplied from the uncorrelated frequency-time transform unit  102 , with a coefficient h 12  which is one of generation parameters supplied from the generation parameter calculation unit  104 . The multiplier  141  supplies a resulting multiplication value h 12 ×X D ′ to the adder  145 . 
     The multiplier  144  multiplies the signal X D ′ supplied from the uncorrelated frequency-time transform unit  102 , with a coefficient h 22  which is one of generation parameters supplied from the generation parameter calculation unit  104 . The multiplier  141  supplies a resulting multiplication value h 22 ×X D ′ to the adder  146 . 
     The adder  145  adds the multiplication value h 11 ×X M  supplied from the multiplier  141  and the multiplication value h 12 ×X D ′ supplied from the multiplier  143 , and outputs a resulting addition value as the left audio signal X L . 
     The adder  146  adds the multiplication value h 21 ×X M  supplied from the multiplier  142  and the multiplication value h 22 ×X D ′ supplied from the multiplier  143 , and outputs a resulting addition value obtained as the right audio signal X R . 
     As described above, the stereo synthesis unit  103  performs weighted addition using generation parameters as indicated in following equation 5 by using as a vector the monaural signal X M , the signal X D ′, the left audio signal X L  and the right audio signal X R  as illustrated in  FIG. 13 .
 
[Equation 5]
 
 X   L   =h   11   ·X   M   +h   12   ·X   D ′
 
 X   R   =h   21   ·X   M   +h   22   ·X   D ′  (5)
 
     In addition, the coefficients h 11 , h 12 , h 21  and h 22  are represented by following equation 6. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     6 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       h 
                       11 
                     
                     = 
                     
                       
                         g 
                         L 
                       
                       · 
                       
                         cos 
                         ⁡ 
                         
                           ( 
                           
                             θ 
                             L 
                           
                           ) 
                         
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       h 
                       12 
                     
                     = 
                     
                       
                         g 
                         L 
                       
                       · 
                       
                         sin 
                         ⁡ 
                         
                           ( 
                           
                             θ 
                             L 
                           
                           ) 
                         
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       h 
                       21 
                     
                     = 
                     
                       
                         g 
                         R 
                       
                       · 
                       
                         cos 
                         ⁡ 
                         
                           ( 
                           
                             θ 
                             R 
                           
                           ) 
                         
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       h 
                       22 
                     
                     = 
                     
                       
                         g 
                         R 
                       
                       · 
                       
                         sin 
                         ⁡ 
                         
                           ( 
                           
                             θ 
                             R 
                           
                           ) 
                         
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   where 
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
             
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     7 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       g 
                       L 
                     
                     = 
                     
                       
                          
                         
                           X 
                           L 
                         
                          
                       
                       
                          
                         
                           X 
                           M 
                         
                          
                       
                     
                   
                   , 
                   
                     
                       g 
                       R 
                     
                     = 
                     
                       
                          
                         
                           X 
                           R 
                         
                          
                       
                       
                          
                         
                           X 
                           M 
                         
                          
                       
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
     In equation 6, an angle θ L  is an angle formed between the vector of the left audio signal X L  and the vector of the monaural signal X M , and an angle θ R  is an angle formed between the vector of the right audio signal X R  and the vector of the monaural signal X M . 
     Meanwhile, the coefficients h 11 , h 12 , h 21  and h 22  are calculated as generation parameters by the generation parameter calculation unit  104 . More specifically, the generation parameter calculation unit  104  calculates g L , g R , θ L  and θ R  from the BC parameters, and calculates the coefficients h 11 , h 12 , h 21  and h 22  from g L , g R , θ L  and θ R  as generation parameters. In addition, details of a method of calculating g L , g R , θ L  and θ R  from BC parameters are disclosed in, for example, Japanese Patent Application Laid-Open No. 2006-325162. 
     In addition, for BC parameters, g L , g R , θ L  and θ R  can also be used, and compressed coded g L , g R , θ L  and θ R  can also be used. Further, for BC parameters, the coefficients h 11 , h 12 , h 21 , and h 22  can also be directly used, or can also be compressed and coded, and used. 
     [Description of Processing of Speech Processing Apparatus] 
       FIG. 14  is a flowchart for describing decoding processing of the speech processing apparatus  100  in  FIG. 9 . This decoding processing is started when multiplexed coded data supplied from the coding apparatus  10  in  FIG. 1  is input to the speech processing apparatus  100 . 
     In step S 11  in  FIG. 14 , the inverse multiplexing unit  101  inversely multiplexes the multiplexed coded data supplied from the coding apparatus  10  in  FIG. 1 , and obtains the coded data and the BC parameters. Further, the inverse multiplexing unit  101  further inversely multiplexes this coded data, and the quantized and entropy-coded frequency spectrum coefficients and the quantization information. Furthermore, the inverse multiplexing unit  101  supplies the quantized and entropy-coded frequency spectrum coefficients, to the entropy decoding unit  52 , and supplies the quantization information to the spectrum inverse quantization unit  53 . Still further, the inverse multiplexing unit  101  supplies the BC parameter to the generation parameter calculation unit  104 . 
     In step S 12 , the entropy decoding unit  52  performs entropy decoding such as Huffman decoding or arithmetic decoding of the frequency spectrum coefficients supplied from the inverse multiplexing unit  101 , and restores the quantized frequency spectrum coefficients. The entropy-decoding unit  52  supplies the frequency spectrum coefficients to the spectrum inverse quantization unit  53 . 
     In step S 13 , the spectrum inverse quantization unit  53  inversely quantizes the quantized frequency spectrum coefficients supplied from the entropy decoding unit  52  based on the quantization information supplied from the inverse multiplexing unit  101 , and restores the frequency spectrum coefficients. Further, the spectrum inverse quantization unit  53  supplies the frequency spectrum coefficients to the uncorrelated frequency-time transform unit  102 . 
     In step S 14 , the uncorrelated frequency-time transform unit  102  generates the monaural signal X M  and the signal X D ′ which are two uncorrelated time domain signals from the frequency spectrum coefficient of the monaural signal X M  obtained as a result of inverse quantization by the spectrum inverse quantization unit  53 . Further, the uncorrelated frequency-time transform unit  102  supplies the monaural signal X M  and the signal X D ′ to the stereo synthesis unit  103 . 
     In step S 15 , the stereo synthesis unit  103  synthesizes the monaural signal X M  and the signal X D ′ supplied from the uncorrelated frequency-time transform unit  102  using the generation parameters supplied from the generation parameter calculation unit  104 . 
     In step S 16 , the generation parameter calculation unit  104  interpolates the BC parameter of a predetermined frame supplied from the inverse multiplexing unit  101 , and calculates the BC parameter of each frame. 
     In step S 17 , the generation parameter calculation unit  104  generates the coefficients h 11 , h 12 , h 21  and h 22  as generation parameters using the BC parameter of a current processing target frame, and supplies the generation parameters to the stereo synthesis unit  103 . 
     In step S 18 , the stereo synthesis unit  103  synthesizes the monaural signal X M  and the signal X D ′ supplied from the uncorrelated frequency-time transform unit  102  using the generation parameters supplied from the generation parameter calculation unit  104 , and generates a stereo signal. Further, the stereo synthesis unit  103  outputs the stereo signal, and processing ends. 
     As described above, the speech processing apparatus  100  generates the monaural signal X M  and the signal X D ′ by performing two types of transform such that the base is orthogonal to the frequency spectrum coefficient of the monaural signal X M . That is, the speech processing apparatus  100  can generate the signal X D ′ using the frequency spectrum coefficient of the monaural signal X M . Consequently, the speech processing apparatus  100  can prevent delay caused by a reverb signal generation unit  71  in  FIG. 7  and an increase in the computation amount and buffer resources compared to the conventional decoding apparatus  40  in  FIG. 4  which has the audio signal decoding unit  42  in  FIG. 5  and the stereo signal generation unit  44  in  FIG. 7 . 
     Further, the IMDCT unit  54  of the conventional decoding apparatus  40  can be reutilized as part of the uncorrelated frequency-time transform unit  102 , so that it is possible to minimize addition of new functions and prevent an increase in a circuit scale and required resources. 
     Second Embodiment 
     Configuration Example of Speech Processing Apparatus According to Second Embodiment 
       FIG. 15  is a block diagram illustrating a configuration example of a speech processing apparatus to which the present invention is applied according to a second embodiment. 
     The same configuration illustrated in  FIG. 15  as the configuration in  FIG. 9  will be assigned the same reference numerals. Overlapping description will be adequately skipped. 
     The configuration of a speech processing apparatus  200  in  FIG. 15  differs from the configuration in  FIG. 9  mainly in that a band division unit  201 , an IMDCT unit  202 , an adder  203  and an adder  204  are additionally provided. 
     The speech processing apparatus  200  decodes, for example, coded data for which the same spatial coding as in a coding apparatus  10  in  FIG. 1  which has an audio signal coding unit  13  in  FIG. 2  is performed, and on which the BC parameter of a high band is multiplexed, and stereo-codes only the monaural signal X M  in a high band. 
     More specifically, the band division unit  201  (division unit) of the speech processing apparatus  200  divides the frequency spectrum coefficient obtained by a spectrum inverse quantization unit  53 , into two groups of high band frequency spectrum coefficients and low band frequency spectrum coefficients according to frequencies. Further, the band division unit  201  supplies the low band frequency spectrum coefficients to the IMDCT unit  202 , and supplies the high band frequency spectrum coefficients to an uncorrelated frequency-time transform unit  102 . 
     The IMDCT unit  202  (third transform unit) performs IMDCT of the low band frequency spectrum coefficients supplied from the band division unit  201 , and obtains a monaural signal X M   low  (third time domain signal) which is a low band time domain signal. The IMDCT unit  202  supplies the low band monaural signal X M   low  to the adder  203  as a low band left audio signal, and to the adder  204  as the low band right audio signal. 
     The adder  203  receives an input of a high band left audio signal X L   High  obtained as a result of processing the high band frequency spectrum coefficient output from the band division unit  201  in the uncorrelated frequency-time transform unit  102  and the stereo synthesis unit  103 . The adder  203  adds the high band left audio signal X L   High  and the low band monaural signal X M   low  supplied from the IMDCT unit  202  as the low band left audio signal, and generates an entire frequency band left audio signal X L . 
     The adder  204  receives an input of a high band right audio signal X R   High  obtained as a result of processing the high band frequency spectrum coefficient output from the band division unit  201  in the uncorrelated frequency-time transform unit  102  and the stereo synthesis unit  103 . The adder  204  adds the high band right audio signal X R   High  and the low band monaural signal X M   low  supplied from the IMDCT unit  202  as the low band right audio signal, and generates an entire frequency band right audio signal X R . 
     [Description of Processing of Speech Processing Apparatus] 
       FIG. 16  is a flowchart for describing decoding processing of the speech processing apparatus  200  in  FIG. 15 . This decoding processing is started when coded data for which the same spatial coding as in the coding apparatus  10  in  FIG. 1  which has the audio signal coding unit  13  in  FIG. 2  is performed and on which a BC parameter of a high band is multiplexed is input to the speech processing apparatus  200 . 
     Steps S 31  to S 33  in  FIG. 16  are the same as processing in steps S 11  to S 13  in  FIG. 14 , and will not be repeatedly described. 
     In step S 34 , the band division unit  201  divides frequency spectrum coefficients obtained by the spectrum inverse quantization unit  53 , into two groups of high band frequency spectrum coefficients and low band frequency spectrum coefficients according to frequencies. Further, the band division unit  201  supplies the low band frequency spectrum coefficients to the IMDCT unit  202 , and supplies the high band frequency spectrum coefficients to the uncorrelated frequency-time transform unit  102 . 
     In step S 35 , the IMDCT unit  202  performs IMDCT of the low band frequency spectrum coefficients supplied from the band division unit  201 , and obtains the monaural signal X M   low  which is a low band time domain signal. The IMDCT unit  202  supplies the low band monaural signal X M   low  to the adder  203  as the low band left audio signal, and to the adder  204  as the low band right audio signal. 
     In step S 36 , stereo signal generation processing is performed for high band frequency spectrum coefficients supplied from the band division unit  201  by the uncorrelated frequency-time transform unit  102 , the stereo synthesis unit  103 , and the generation parameter calculation unit  104 . More specifically, the uncorrelated frequency-time transform unit  102 , the stereo synthesis unit  103  and the generation parameter calculation unit  104  perform processing in steps S 14  to S 18  in  FIG. 14 . The resulting high band left audio signal X L   High  and high band right audio signal X R   High  are input to the adder  203  and the adder  204 , respectively. 
     In step S 37 , the adder  203  adds the low band monaural signal X M   low  supplied from the IMDCT unit  202  as a low band left audio signal and the high band left audio signal X L   High  supplied from the uncorrelated frequency-time transform unit  102 , and generates an entire frequency band left audio signal X L . Further, the adder  203  outputs the entire frequency band left audio signal X L . 
     In step S 38 , the adder  204  adds the low band monaural signal X M   low  supplied from the IMDCT unit  202  as the low band right audio signal and the high band right audio signal X R   High  supplied from the uncorrelated frequency-time transform unit  102 , and generates the entire frequency band right audio signal X R . Further, the adder  204  outputs this entire frequency band right audio signal X R . 
     As described above, the speech processing apparatus  200  decodes coded data of the entire frequency band monaural signal X M , and stereo-codes only the high band. Consequently, it is possible to prevent sound from being unnatural due to stereo coding of the low band monaural signal X M . 
     In addition, although, with the speech processing apparatus  200 , the band division unit  201  divides frequency spectrum coefficients into high band frequency spectrum coefficients and low band frequency spectrum coefficients, the band division band unit  201  may divide frequency spectrum coefficients into predetermined frequency band frequency spectrum coefficients and other frequency band frequency spectrum coefficients. That is, whether or not stereo coding is performed may be selected depending on whether a frequency band is a predetermined frequency band or other frequency bands instead of whether a frequency band is a low band or a high band. 
     Third Embodiment 
     Configuration Example of Speech Processing Apparatus According to Third Embodiment 
       FIG. 17  is a block diagram illustrating a configuration example of a speech processing apparatus to which the present invention is applied according to a third embodiment. 
     The same configuration illustrated in  FIG. 17  as the configurations in  FIGS. 4 ,  6  and  9  will be assigned the same reference numerals. Overlapping description will be adequately skipped. 
     A configuration of a speech processing apparatus  300  in  FIG. 17  differs from a configuration of a decoding apparatus  40  in  FIG. 4  which has an audio signal decoding unit  42  in  FIG. 6  and a stereo signal generation unit  44  in  FIG. 7  mainly in that an inverse multiplexing unit  301  is provided instead of an inverse multiplexing unit  41  and an inverse multiplexing unit  61 , IMDCT units  304 - 1  to  304 -(N−1) are provided instead of IMDCT unit  64 - 1  to IMDCT unit  64 -(N−1), a stereo coding unit  305  is provided instead of an IMDCT unit  64 -N and a stereo signal generation unit  44  and a generation parameter calculation unit  104  and a synthesis filter bank  306  are provided instead of a generation parameter calculation unit  43  and a synthesis filter bank  65 . 
     The speech processing apparatus  300  in  FIG. 17  decodes, for example, coded data for which the same spatial coding as in a coding apparatus  10  in  FIG. 1  which has an audio signal coding unit  13  in  FIG. 3  is performed, and on which a BC parameter of a predetermined subband signal is multiplexed. 
     More specifically, the inverse multiplexing unit  301  of the speech processing apparatus  300  corresponds to the inverse multiplexing unit  41  in  FIG. 4  and the inverse multiplexing unit  61  in  FIG. 6 . That is, the inverse multiplexing unit  301  receives an input of coded data for which the same spatial coding as in the coding apparatus  10  in  FIG. 1  which has the audio signal coding unit  13  in  FIG. 3  is performed, and in which a BC parameter of a predetermined subband signal is multiplexed. The inverse multiplexing unit  301  inversely multiplexes the input coded data, and obtains the coded data and the BC parameter of the predetermined subband signal. Further, the inverse multiplexing unit  301  supplies the BC parameter of the predetermined subband signal to the generation parameter calculation unit  104 . 
     Furthermore, the inverse multiplexing unit  301  inversely multiplexes the coded data, and obtains quantized and entropy-coded frequency spectrum coefficients of N subband signals and quantization information. The inverse multiplexing unit  301  supplies the quantized and entropy-coded frequency spectrum coefficients of the N subband signals to the entropy decoding unit  62 , and supplies the quantization information to the spectrum inverse quantization unit  63 . 
     The IMDCT units  304 - 1  to  304 -(N−1) (third transform unit) and the stereo coding unit  305  receive an input of the frequency spectrum coefficients of the N subband signals restored by the spectrum inverse quantization unit  63  one by one. 
     The IMDCT units  304 - 1  to  304 -(N−1) each perform IMDCT of the input frequency spectrum coefficient, and transform the frequency spectrum coefficient into a subband signal X M   i  (i=1, 2, . . . and N−1) of the monaural signal X M  which is a time domain signal. The IMDCT units  304 - 1  to  304 -(N−1) each supply the subband signal X M   i  to the synthesis filter bank  306  as a left audio signal X L   i  and a right audio signal X R   i . 
     The stereo coding unit  305  includes an uncorrelated frequency-time transform unit  102  and a stereo synthesis unit  103  in  FIG. 9 . The stereo coding unit  305  generates a subband signal X L   A  of a left audio signal and a subband signal X R   A  of a right audio signal which are time domain signal, from frequency spectrum coefficients of the predetermined subband signal input from the spectrum inverse quantization unit  63 , using the generation parameters generated by the generation parameter calculation unit  104 . Further, the stereo coding unit  305  supplies the left subband signal X L   A  and the right subband signal X R   A  to the synthesis filter bank  306 . 
     The synthesis filter bank  306  (addition unit) includes a left synthesis filter bank for synthesizing a subband signal of a left audio signal, and a right synthesis filter bank for synthesizing a subband signal of a right audio signal. The left synthesis filter bank of the synthesis filter bank  306  synthesizes left subband signals X L   1  to X L   N-1  from the IMDCT units  304 - 1  to  304 -(N−1), and the left subband signal X L   A  from the stereo coding unit  305 . Further, the left synthesis filter bank outputs the entire frequency band left audio signal X L  obtained as a result of synthesis. 
     Furthermore, the right synthesis filter bank of the synthesis filter bank  306  synthesizes right subband signals X R   1  to X R   N-1  from the IMDCT units  304 - 1  to  304 -(N−1), and the right subband signal X R   A  from the stereo coding unit  305 . Still further, the right synthesis filter bank outputs the entire frequency band right audio signal X R  obtained as a result of synthesis. 
     In addition, although the speech processing apparatus  300  in  FIG. 17  stereo-codes one subband signal alone, the speech processing apparatus  300  can stereo-codes a plurality of subband signals. Further, a subband signal which is stereo-coded may be dynamically set on a coding side instead of being set in advance. In this case, for example, information for specifying a subband signal which is a stereo coding target is included in a BC parameter. 
     [Description of Processing of Speech Processing Apparatus] 
       FIG. 18  is a flowchart for describing decoding processing of the speech processing apparatus  300  in  FIG. 17 . This decoding processing is started when, for example, coded data for which the same spatial coding as in the coding apparatus  10  in  FIG. 1  which has the audio signal coding unit  13  in  FIG. 3  is performed, and on which a BC parameter of a predetermined subband signal is multiplexed is input to the speech processing apparatus  300 . 
     In step S 51  in  FIG. 18 , the inverse multiplexing unit  301  inversely multiplexes the input multiplexed coded data, and obtains the coded data and the BC parameter of the predetermined subband signal. Further, the inverse multiplexing unit  301  supplies the BC parameter of the predetermined subband signal to the generation parameter calculation unit  104 . Furthermore, the inverse multiplexing unit  301  inversely multiplexes the coded data, and obtains quantized and entropy-coded frequency spectrum coefficients of N subband signals and quantization information. The inverse multiplexing unit  301  supplies the quantized and entropy-coded frequency spectrum coefficients of the N subband signals to the entropy decoding unit  62 , and supplies the quantization information to the spectrum inverse quantization unit  63 . 
     In step S 52 , the entropy decoding unit  62  entropy-decodes the frequency spectrum coefficients of the N subband signals supplied from the inverse multiplexing unit  101 , and supplies the frequency spectrum coefficients to the spectrum inverse quantization unit  63 . 
     In step S 53 , the spectrum inverse quantization unit  63  inversely quantizes the frequency spectrum coefficients of the N subband signals supplied from the entropy decoding unit  62  and obtained as a result of entropy decoding, based on the quantization information supplied from the inverse multiplexing unit  301 . Further, the spectrum inverse quantization unit  63  supplies the resulting restored frequency spectrum coefficients of the N subband signals, to the IMDCT units  304 - 1  to  304 -(N−1) and the stereo coding unit  305  one by one. 
     In step S 54 , the IMDCT units  304 - 1  to  304 -(N−1) each perform IMDCT of the frequency spectrum coefficient supplied from the spectrum inverse quantization unit  63 . Further, the IMDCT units  304 - 1  to  304 -(N−1) each supply the resulting subband signal X M   i  (i=1, 2, . . . and N−1) of a monaural signal to the synthesis filter bank  306  as the subband signal X L   i  of the left audio signal and the subband signal X L   i  of the right audio signal. 
     In step S 55 , the stereo coding unit  305  performs stereo signal generation processing of the frequency spectrum coefficient of a predetermined subband signal supplied from the spectrum inverse quantization unit  63 , using the generation parameters supplied from the generation parameter calculation unit  104 . Further, the stereo coding unit  305  supplies the resulting subband signal X L   A  of the left audio signal and subband signal X R   A  of the right audio signal which are time domain signals, to the synthesis filter bank  306 . 
     In step S 56 , the left synthesis filter bank of the synthesis filter bank  306  synthesizes all subband signals of left audio signals supplied from the IMDCT units  304 - 1  to  304 -(N−1) and the stereo coding unit  305 , and generates the entire frequency band left audio signal X L . Further, the left synthesis filter bank outputs this entire frequency band left audio signal X L . 
     In step S 57 , the right synthesis filter bank of the synthesis filter bank  306  synthesizes all subband signals of right audio signals supplied from the IMDCT units  304 - 1  to  304 -(N−1) and the stereo coding unit  305 , and generates the entire frequency band right audio signal X R . Further, the right synthesis filter bank outputs this entire frequency band right audio signal X R . 
     Fourth Embodiment 
     Configuration Example of Speech Processing Apparatus According to Fourth Embodiment 
       FIG. 19  is a block diagram illustrating a configuration example of a speech processing apparatus to which the present invention is applied according to a fourth embodiment. 
     The same configuration illustrated in  FIG. 19  as the configuration in  FIG. 15  will be assigned the same reference numerals. Overlapping description will be adequately skipped. 
     The configuration of a speech processing apparatus  400  in  FIG. 19  differs from the configuration in  FIG. 15  mainly in that a spectrum separation unit  401  is provided instead of a band division unit  201 , IMDCTs  402  and  403  are provided instead of an IMDCT unit  202 , and an adder  404  and an adder  405  are provided instead of an adder  203  and an adder  204 . 
     The speech processing apparatus  400  decodes coded data for which intensity coding is performed, and on which a BC parameter at a frequency equal to or more than an intensity start frequency Fis is multiplexed instead of a conventional level ratio of inter-channel frequency spectrum coefficients. 
     That is, the coded data decoded by the speech processing apparatus  400  is generated by a coding apparatus which detects the BC parameter by, for example, downmixing a coding target stereo signal to a monaural signal X M  and extracting the resulting monaural signal X M  and a component at a frequency equal to or more than the intensity start frequency Fis of the coding target stereo signal by means of, for example, a bypass filter. 
     The spectrum separation unit  401  (separation unit) of the speech processing apparatus  400  obtains frequency spectrum coefficients restored by a spectrum inverse quantization unit  53 . The spectrum separation unit  401  separates this frequency spectrum coefficient into a frequency spectrum coefficient of a stereo signal at a frequency lower than the intensity start frequency Fis and a frequency spectrum coefficient of a monaural signal X M   high  at a frequency equal to or more than the intensity start frequency Fis. The spectrum separation unit  401  supplies the frequency spectrum coefficient of the left audio signal X L   low  of the stereo signal at a frequency lower than the intensity start frequency Fis, to the IMDCT unit  402 , and supplies the frequency spectrum coefficient of the right audio signal X R   low  to the IMDCT unit  403 . Further, the spectrum separation unit  401  supplies the frequency spectrum coefficient of the monaural signal X M   high  to an uncorrelated frequency-time transform unit  102 . 
     The IMDCT unit  402  (third transform unit) performs IMDCT of the frequency spectrum coefficient of the left audio signal X L   low  supplied from the spectrum separation unit  401 , and supplies the resulting left audio signal X L   low  to the adder  404 . 
     The IMDCT unit  403  (third transform unit) performs IMDCT of the frequency spectrum coefficient of the right audio signal X R   low  supplied from the spectrum separation unit  401 , and supplies the resulting right audio signal X R   low  to the adder  405 . 
     The adder  404  (addition unit) adds the left audio signal X L   high  which is generated by the stereo synthesis unit  103  and which is a time domain signal at a frequency equal to or more than an intensity start frequency Fis, and the left audio signal X L   low  supplied from the IMDCT unit  402 . The adder  404  outputs the resulting audio signal as the entire frequency band left audio signal X L . 
     The adder  405  (addition unit) adds the right audio signal X R   high  which is generated by the stereo synthesis unit  103  and which is a time domain signal at a frequency equal to or more than the intensity start frequency Fis, and the right audio signal X R   low  supplied from the IMDCT unit  402 . The adder  405  outputs the resulting audio signal as the entire frequency band right audio signal X R . 
     As described above, the speech processing apparatus  400  stereo-codes a component of the frequency equal to or more than the intensity start frequency Fis monaural-coded by intensity coding, using the BC parameter multiplexed on intensity-coded data. Consequently, it is possible to restore a stereophonic effect of the component of the frequency equal to or more than the intensity start frequency Fis compared to an intensity decoding apparatus which performs stereo-coding using a conventional level ratio of inter-channel frequency spectrum coefficients. 
     [Description of Processing of Speech Processing Apparatus] 
       FIG. 20  is a flowchart for describing decoding processing of the speech processing apparatus  400  in  FIG. 19 . This decoding processing is started when, for example, coded data which is intensity-coded and on which the BC parameter of the frequency equal to or more than the intensity start frequency Fis is multiplexed is input. 
     Processing in steps S 71  to S 73  in  FIG. 20  are the same as the processing in steps S 31  to S 33  in  FIG. 16 , and therefore will not be described. 
     In step S 74 , the spectrum separation unit  401  separates the frequency spectrum coefficients restored by the spectrum inverse quantization unit  53  into frequency spectrum coefficients of stereo signals at a frequency lower than the intensity start frequency Fis and the frequency spectrum coefficient of the monaural signal X M   high  at a frequency equal to or more than the intensity start frequency Fis. The spectrum separation unit  401  supplies the frequency spectrum coefficient of the left audio signal X L   low  of the stereo signal at a frequency lower than the intensity start frequency Fis, to the IMDCT unit  402 , and the frequency spectrum coefficient of the right audio signal X R   low  to the IMDCT unit  403 . Further, the spectrum separation unit  401  supplies the frequency spectrum coefficient of the monaural signal X M   high  to the uncorrelated frequency-time transform unit  102 . 
     In step S 75 , the IMDCT unit  402  performs IMDCT of the frequency spectrum coefficient of the left audio signal X L   low  supplied from the spectrum separation unit  401 . Further, the IMDCT unit  402  supplies the resulting left audio signal X L   low  to the adder  404 . 
     In step S 76 , the IMDCT unit  403  performs IMDCT of the frequency spectrum coefficient of the right audio signal X R   low  supplied from the spectrum separation unit  401 . Further, the IMDCT unit  403  supplies the resulting right audio signal X R   low  to the adder  405 . 
     In step S 77 , the uncorrelated frequency-time transform unit  102 , the stereo synthesis unit  103  and the generation parameter calculation unit  104  perform stereo signal generation processing of the frequency spectrum coefficient of the monaural signal X M   high  from the spectrum separation unit  401 . The resulting left audio signal X L   high  which is a time domain signal is supplied to the adder  404 , and the right audio signal X R   high  is supplied to the adder  405 . 
     In step S 78 , the adder  404  adds the left audio signal X L   low  at a frequency lower than the intensity start frequency Fis from the IMDCT unit  402  and the left audio signal X L   high  at a frequency equal to or more than the intensity start frequency Fis from the stereo synthesis unit  103 , and generates the entire frequency band left audio signal X L . Further, the adder  404  outputs this left audio signal X L . 
     In step S 79 , the adder  405  adds the right audio signal X R   low  at a frequency lower than the intensity start frequency Fis from the IMDCT unit  403  and the right audio signal X R   high  at a frequency equal to or more than the intensity start frequency Fis from the stereo synthesis unit  103 , and generates the entire frequency band right audio signal X R . Further, the adder  405  outputs this right audio signal X R . 
     In addition, although, with the above description, a speech processing apparatus  100  ( 200 ,  300  and  400 ) decodes coded data which is time-frequency transformed by MDCT, and therefore IMDCT is performed upon frequency-time transform, IMDST is performed upon frequency-time transform when coded data which is time-frequency transformed by MDST is decoded. 
     Further, although, with the above description, the uncorrelated time-frequency transform unit  102  uses IMDCT transform and IMDST transform where bases are orthogonal to each other, other lapped orthogonal transform such as sine transform or cosine transform may be used. 
     [Description of Computer to which Present Invention is Applied] 
     Next, a series of the above processing can be executed by hardware or by software. When a series of the processing are executed by software, a program configuring this software is installed to, for example, a general-purpose computer. 
       FIG. 21  illustrates a configuration example of a computer in which a program for executing a series of the above processing are installed according to an embodiment. 
     The program can be recorded in advance in a memory unit  508  or a ROM (Read Only Memory)  502  which is a recording medium built in the computer. 
     Alternatively, the program can be stored (recorded) in a removable media  511 . This removable media  511  can be provided as so-called package software. Meanwhile, the removable media  511  includes, for example, a flexible disc, a CD-ROM (Compact Disc Read Only Memory), a MO (Magneto Optical) disc, a DVD (Digital Versatile Disc), a magnetic disc and a semiconductor memory. 
     In addition, the program can be installed to a computer from the above removable media  511  through a drive  510 , and, in addition, may be downloaded to a computer through a communication network or a broadcasting network or installed in the built-in memory unit  508 . That is, the program can be wirelessly transferred, for example, from a download site to a computer through a digital satellite broadcasting satellite, or can be transferred to a computer by way of a wire through a network such as LAN (Local Area Network) or Internet. 
     The computer has a built-in CPU (Central Processing Unit)  501 , and the CPU  501  is connected with an input/output interface  505  through a bus  504 . 
     The CPU  501  executes the program stored in the ROM  502  according to a command when receiving an input of the command according to, for example, a user&#39;s operation of an input unit  506  through the input/output interface  505 . Alternatively, the CPU  501  loads the program stored in the memory unit  508  to a RAM (Random Access Memory)  503  and executes the program. 
     Thus, the CPU  501  executes processing according to the above flowchart or processing executed by the configuration in the above block diagram. Further, the CPU  501  outputs this processing result from an output unit  507  through the input/output interface  505 , transmits the processing result from a communication unit  509  or records the processing result in the memory unit  508 . 
     In addition, the input unit  506  includes a keyboard, a mouse or a microphone. Further, the output unit  507  includes a LCD (Liquid Crystal Display) or speakers. 
     Meanwhile, in this description, processing executed by the computer according to the program does not necessarily need to be executed in a chronological order disclosed as a flowchart. That is, the processing executed by the computer according to the program include processing (such as parallel processing or processing by an object) executed in parallel or individually. 
     Further, the program may be processed by one computer (processor) or processed in a distributed manner by a plurality of computers. Furthermore, the program may be transferred to a distant computer and executed. 
     The present invention is applicable to a pseudo stereo coding technique for audio signals. 
     The embodiments of the present invention are by no means limited to the above embodiments, and can be variously modified within a scope which does not deviate from the spirit of the present invention. 
     REFERENCE SIGNS LIST 
     
         
           54  IMDCT unit 
           100  Speech processing apparatus 
           101  Inverse multiplexing unit 
           103  Stereo synthesis unit 
           111  IMDST unit 
           121  Spectrum inversion unit 
           122  IMDCT unit 
           123  Sign inversion unit 
           200  Speech processing apparatus 
           201  Band division unit 
           202  IMDCT unit 
           203 ,  204  Adder 
           300  Speech processing apparatus 
           301  Inverse multiplexing unit 
           304 - 1  to  304 -N IMDCT unit 
           305  Stereo coding unit 
           306  Synthesis filter bank 
           400  Speech processing apparatus 
           401  Spectrum separation unit 
           402 ,  403  IMDCT unit 
           404 ,  405  Adder