Patent Publication Number: US-8121850-B2

Title: Encoding apparatus and encoding method

Description:
TECHNICAL FIELD 
     The present invention relates to a encoding apparatus and encoding method used in a communication system for encoding and transmitting signals. 
     BACKGROUND ART 
     When speech/sound signals are transmitted in a packet communication system represented by Internet communication, mobile communication system and so on, compression/coding techniques are often used to improve the transmission efficiency of speech/sound signals. Furthermore, in the recent years, while speech/sound signals are being encoded simply at low bit rates, there is a growing demand for techniques for encoding speech/sound signals of wider band. 
     To meet this demand, studies are underway to develop various techniques for encoding wideband speech/sound signals without drastically increasing the amount of encoded information. For example, patent document 1 discloses a technique of generating features of the high frequency band region in the spectral data obtained by converting an input acoustic signal of a certain period, as side information, and outputting this information together with encoded information of the low band region. To be more specific, the spectral data of the high frequency band region is divided into a plurality of groups, and, in each group, regards the spectrum of the low band region that is the most similar to the spectrum of the group, as the side information mentioned above. 
     Furthermore, patent document 2 discloses a technique of dividing the high band signal into a plurality of subbands, deciding, per subband, the degree of similarity between the signal of each subband and the low band signal, and changing the configurations of side information (i.e. the amplitude parameter of the subband, position parameter of a similar low band signal, residual signal parameter between the high band the and the low band) according to the decision result. 
     Patent Document 1: Japanese Patent Application Laid-Open No. 2003-140692 
     Patent Document 2: Japanese Patent Application Laid-Open No. 2004-004530 
     DISCLOSURE OF INVENTION 
     Problems to be Solved by the Invention 
     However, although the techniques disclosed in above-described patent document 1 and patent document 2 decide a low band signal that correlates with or that is similar to a high band region to generate a high band signal (i.e. spectral data of a high band region), this is performed per subband (group) of the high band signal, and, as a result, the amount of processing of calculations becomes enormous. Furthermore, since the above-described processing is carried out on a per band basis, not only the amount of calculation, but also the amount of information required to encode side information increases. 
     Furthermore, the techniques disclosed in above-described patent document 1 and patent document 2 decide the degree of similarity of spectral data of the high band region of an input signal in the same way as spectral data of the low band region of the input signal, and, given that spectral data of the low band region is not taken into account if it is distorted by quantization, a severe sound quality degradation is anticipated when spectral data of the low band region is distorted by quantization. 
     It is therefore an object of the present invention to provide an encoding apparatus and encoding method that make it possible to encode spectral data of the high band region of a wideband signal based on spectral data of the low band region of the signal by reducing the number of samples to be processed and furthermore obtain a decoded signal of high quality even when a severe quantization distortion occurs in the spectral data of the low band region. 
     Means for Solving the Problem 
     The encoding apparatus of the present invention adopts a configuration including: a first encoding section that encodes an input signal to generate first encoded information; a decoding section that decodes the first encoded information to generate a decoded signal; a orthogonal transform section that orthogonal-transforms the input signal and the decoded signal to generate orthogonal transform coefficients for the signals; a second encoding section that generates second encoded information representing a high band part in the orthogonal transform coefficients of the decoded signal, based on the orthogonal transform coefficients of the input signal and the orthogonal transform coefficients of the decoded signal; and an integration section that integrates the first encoded information and the second encoded information. 
     The encoding method of the present invention includes: a first encoding step of encoding an input signal to generate first encoded information; a decoding step of decoding the first encoded information to generate a decoded signal; a orthogonal transform step of orthogonal-transforming the input signal and the decoded signal to generate orthogonal transform coefficients for the signals; a second encoding step of generating second encoded information representing a high band part of the orthogonal transform coefficients of the decoded signal based on the orthogonal transform coefficients of the input signal and the orthogonal transform coefficients of the decoded signal; and an integration step of integrating the first encoded information and the second encoded information. 
     Advantageous Effect of the Invention 
     In accordance with the present invention, it is possible to encode spectral data of the high band region of a wideband signal based on spectral data of the low band region of the wideband signal by reducing the number of samples to be processed and furthermore obtain a decoded signal of high quality even when a severe quantization distortion occurs in the spectral data of the low band region. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram showing a configuration of a communication system provided with a encoding apparatus and decoding apparatus according to Embodiments 1 and 2 of the present invention; 
         FIG. 2  is a block diagram showing a configuration of the encoding apparatus shown in  FIG. 1 ; 
         FIG. 3  is a block diagram showing an internal configuration of the low band encoding section shown in  FIG. 2 ; 
         FIG. 4  is a block diagram showing an internal configuration of the low band decoding section shown in  FIG. 2 ; 
         FIG. 5  is a block diagram showing an internal configuration of the high band encoding section shown in  FIG. 2 ; 
         FIG. 6  shows, conceptually, a similar-part search by the a similar-part search section shown in  FIG. 5 ; 
         FIG. 7  shows, conceptually, the processing in the amplitude ratio adjusting section shown in  FIG. 5 ; 
         FIG. 8  is a block diagram showing a configuration of the decoding apparatus shown in  FIG. 1 ; and 
         FIG. 9  is a block diagram showing an internal configuration of the high band decoding section shown in  FIG. 8 . 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Embodiments of the present invention will be explained below in detail with reference to the accompanying drawings. 
     Embodiment 1 
       FIG. 1  is a block diagram showing a configuration of a communication system with a encoding apparatus and decoding apparatus according to Embodiment 1 of the present invention. In  FIG. 1 , the communication system is provided with a encoding apparatus and decoding apparatus, which are able to communicate with each other via a channel. The channel may be wireless or wired or may be both wireless and wired. 
     Encoding apparatus  101  divides an input signal every N samples (N is a natural number), regards N samples one frame, and performs encoding per frame. Here, suppose the input signal to be encoded is expressed as “x n ” (n=0, . . . , N−1). n indicates the (n+1)-th signal element of the input signal divided every N samples. The encoded input information (i.e. encoded information) is transmitted to decoding apparatus  103  via channel  102 . 
     Decoding apparatus  103  receives the encoded information transmitted from encoding apparatus  101  via channel  102 , decodes the signal and obtains an output signal. 
       FIG. 2  is a block diagram showing an internal configuration of encoding apparatus  101  shown in  FIG. 1 . When the sampling frequency of the input signal is SR input , down-sampling processing section  201  down-samples the sampling frequency of the input signal from SR input  to SR base  (SR base &lt;SR input ), and outputs the down-sampled input signal to low band encoding section  202  as the down-sampled input signal. 
     Low band encoding section  202  encodes the down-sampled input signal outputted from down-sampling processing section  201  using a CELP type speech encoding method, to generate a low band component encoded information, and outputs the low band component encoded information generated, to low band decoding section  203  and encoded information integration section  207 . The details of low band encoding section  202  will be described later. 
     Low band decoding section  203  decodes the low band component encoded information outputted from low band encoding section  202  using a CELP type speech decoding method, to generate a low band component decoded signal, and outputs the low band component decoded signal generated, to up-sampling processing section  204 . The details of low band decoding section  203  will be described later. 
     Up-sampling processing section  204  up-samples the sampling frequency of the low band component decoded signal outputted from low band decoding section  203  from SR base  to SR input , and outputs the up-sampled low band component decoded signal to orthogonal transform processing section  205  as the up-sampled low band component decoded signal. 
     Orthogonal transform processing section  205  contains buffers buf  1   n  and buf  2   n  (n=0, . . . , N−1) in association with the aforementioned signal elements, and initializes the buffers using 0 as the initial value according to equation 1 and equation 2, respectively.
 
(Equation 1)
 
 buf 1 n =0( n= 0 , . . . , N− 1)  [1]
 
(Equation 2)
 
 buf 2 n =0 ( n= 0 , . . . , N− 1)  [2]
 
     Next, as for the orthogonal transform processing in orthogonal transform processing section  205 , the calculation procedures and data output to the internal buffers will be explained. 
     Orthogonal transform processing section  205  applies the modified discrete cosine transform (“MDCT”) to input signal x n  and up-sampled low band component decoded signal y n  outputted from up-sampling processing section  204  and calculates MDCT coefficients X k  of the input signal and MDCT coefficients Y k  of up-sampled low band component decoded signal y n  according to equation 3 and equation 4. 
     
       
         
           
             
               
                 
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     Here, k is the index of each sample in a frame. Orthogonal transform processing section  205  calculates x n ′, which is a vector combining input signal x n  and buffer buf  1   n , according to following equation 5. Furthermore, orthogonal transform processing section  205  calculates which is a vector combining up-sampled low band component decoded signal y n  and buffer buf  2   n , according to following equation 6. 
     
       
         
           
             
               
                 
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     Next, orthogonal transform processing section  205  updates buffers buf  1   n  and buf  2   n  according to equation 7 and equation 8.
 
(Equation 7)
 
 buf 1 n =x n  ( n= 0 , . . . N− 1)  [7]
 
(Equation 8)
 
 buf 2 n =y n  ( n= 0 , . . . N− 1)  [8]
 
     Orthogonal transform processing section  205  outputs the MDCT coefficients X k  of the input signal and MDCT coefficients Y k  of the up-sampled low band component decoded signal, to high band encoding section  206 . 
     High band encoding section  206  generates a high band component encoded information from the values of MDCT coefficients X k  of the input signal outputted from orthogonal transform processing section  205  and MDCT coefficients Y k  of the up-sampled low band component decoded signal, and outputs the high band component encoded information generated, to encoded information integration section  207 . The details of high band encoding section  206  will be described later. 
     Encoded information integration section  207  integrates the low band component encoded information outputted from low band encoding section  202  with the high band component encoded information outputted from high band encoding section  206 , adds, if necessary, a transmission error code and so on, to the integrated encoded information, and outputs the resulting code to channel  102  as encoded information. 
     Next, the internal configuration of low band encoding section  202  shown in  FIG. 2  will be explained using  FIG. 3 . Here, a case where low band encoding section  202  performs CELP type speech encoding, will be explained. Pre-processing section  301  performs high pass filter processing of removing the DC component, waveform shaping processing or pre-emphasis processing, with the input signal, to improve the performance of subsequent encoding processing, and outputs the signal (Xin) subjected to such processing to LPC analysis section  302  and addition section  305 . 
     LPC analysis section  302  performs a linear predictive analysis using Xin outputted from pre-processing section  301 , and outputs the analysis result (linear predictive analysis coefficient) to LPC quantization section  303 . 
     LPC quantization section  303  performs quantization processing of the linear predictive coefficient (LPC) outputted from LPC analysis section  302 , outputs the quantized LPC to synthesis filter  304  and also outputs a code (L) representing the quantized LPC, to multiplexing section  314 . 
     Synthesis filter  304  performs a filter synthesis on an excitation outputted from addition section  311  (described later) using a filter coefficient based on the quantized LPC outputted from LPC quantization section  303 , generates a synthesized signal and outputs the synthesized signal to addition section  305 . 
     Addition section  305  inverts the polarity of the synthesized signal outputted from synthesis filter  304 , adds the synthesized signal with an inverse polarity to Xin outputted from pre-processing section  301 , thereby calculating an error signal, and outputs the error signal to perceptual weighting section  312 . 
     Adaptive excitation codebook  306  stores excitation outputted in the past from addition section  311  in a buffer, extracts one frame of samples from the past excitation specified by the signal outputted from parameter determining section  313  (described later) as an adaptive excitation vector, and outputs this vector to multiplication section  309 . 
     Quantization gain generation section  307  outputs a quantization adaptive excitation gain and quantization fixed excitation gain specified by the signal outputted from parameter determining section  313 , to multiplication section  309  and multiplication section  310 , respectively. 
     Fixed excitation codebook  308  outputs a pulse excitation vector having a shape specified by a signal outputted from parameter determining section  313 , to multiplication section  310  as a fixed excitation vector. A vector produced by multiplying the pulse excitation vector by a spreading vector may also be outputted to multiplication section  310  as a fixed excitation vector. 
     Multiplication section  309  multiplies the adaptive excitation vector outputted from adaptive excitation codebook  306  by the quantization adaptive excitation gain outputted from quantization gain generation section  307 , and outputs the multiplication result to addition section  311 . Furthermore, multiplication section  310  multiplies the fixed excitation vector outputted from fixed excitation codebook  308  by the quantization fixed excitation gain outputted from quantization gain generation section  307 , and outputs the multiplication result to addition section  311 . 
     Addition section  311  adds up the adaptive excitation vector multiplied by the gain outputted from multiplication section  309  and the fixed excitation vector multiplied by the gain outputted from multiplication section  310 , and outputs an excitation, which is the addition result, to synthesis filter  304  and adaptive excitation codebook  306 . The excitation outputted to adaptive excitation codebook  306  is stored in the buffer of adaptive excitation codebook  306 . 
     Perceptual weighting section  312  assigns perceptual a weight to the error signal outputted from addition section  305 , and outputs the resulting error signal to parameter determining section  313  as the coding distortion. 
     Parameter determining section  313  selects the adaptive excitation vector, fixed excitation vector and quantization gain that minimize the coding distortion outputted from perceptual weighting section  312  from adaptive excitation codebook  306 , fixed excitation codebook  308  and quantization gain generation section  307 , respectively, and outputs an adaptive excitation vector code (A), fixed excitation vector code (F) and quantization gain code (G) showing the selection results, to multiplexing section  314 . 
     Multiplexing section  314  multiplexes the code (L) showing the quantized LPC outputted from LPC quantization section  303 , the adaptive excitation vector code (A), fixed excitation vector code (F) and quantization gain code (G) outputted from parameter determining section  313  and outputs the multiplexed code to low band decoding section  203  and encoded information integration section  207  as a low band component encoded information. 
     Next, an internal configuration of low band decoding section  203  shown in  FIG. 2  will be explained using  FIG. 4 . Here, a case where low band decoding section  203  performs CELP type speech decoding will be explained. 
     Demultiplexing section  401  divides the low band component encoded information outputted from low band encoding section  202  into individual codes (L), (A), (G) and (F). The divided LPC code (L) is outputted to LPC decoding section  402 , the divided adaptive excitation vector code (A) is outputted to adaptive excitation codebook  403 , the divided quantization gain code (G) is outputted to quantization gain generation section  404  and the divided fixed excitation vector code (F) is outputted to fixed excitation codebook  405 . 
     LPC decoding section  402  decodes the quantized LPC from the code (L) outputted from demultiplexing section  401 , and outputs the decoded quantized LPC to synthesis filter  409 . 
     Adaptive excitation codebook  403  extracts one frame of samples from the past excitation specified by the adaptive excitation vector code (A) outputted from demultiplexing section  401  as an adaptive excitation vector and outputs the adaptive excitation vector to multiplication section  406 . 
     Quantization gain generation section  404  decodes the quantization adaptive excitation gain and quantization fixed excitation gain specified by the quantization gain code (G) outputted from demultiplexing section  401 , outputs the quantization adaptive excitation gain to multiplication section  406  and outputs the quantization fixed excitation gain to multiplication section  407 . 
     Fixed excitation codebook  405  generates a fixed excitation vector specified by the fixed excitation vector code (F) outputted from demultiplexing section  401 , and outputs the fixed excitation vector to multiplication section  407 . 
     Multiplication section  406  multiplies the adaptive excitation vector outputted from adaptive excitation codebook  403  by the quantization adaptive excitation gain outputted from quantization gain generation section  404 , and outputs the multiplication result to addition section  408 . Furthermore, multiplication section  407  multiplies the fixed excitation vector outputted from fixed excitation codebook  405  by the quantization fixed excitation gain outputted from quantization gain generation section  404 , and outputs the multiplication result to addition section  408 . 
     Addition section  408  adds up the adaptive excitation vector multiplied by the gain outputted from multiplication section  406  and the fixed excitation vector multiplied by the gain outputted from multiplication section  407  to generate an excitation, and outputs the excitation to synthesis filter  409  and adaptive excitation codebook  403 . 
     Synthesis filter  409  performs a filter synthesis of the excitation outputted from addition section  408  using the filter coefficient decoded by LPC decoding section  402 , and outputs the synthesized signal to post-processing section  410 . 
     Post-processing section  410  applies processing for improving the subjective quality of speech such as formant emphasis and pitch emphasis and processing for improving the subjective quality of stationary noise, to the signal outputted from synthesis filter  409 , and outputs the resulting signal to up-sampling processing section  204  as a low band component decoded signal. 
     Next, an internal configuration of high band encoding section  206  shown in  FIG. 2  will be explained using  FIG. 5 . A similar-part search section  501  calculates the search result position t MIN  (t=t MIN ) by minimizing the error D between M samples of MDCT coefficients Y k  of the up-sampled low band component decoded signal outputted from orthogonal transform processing section  205  and MDCT coefficients X k  of the input signal outputted from orthogonal transform processing section  205 . Similar-part search section  501  may also calculate the gain β at t min . The error D and gain β can be calculated from equation 9 and equation 10, respectively. 
                   (     Equation   ⁢           ⁢   9     )                           D   =         ∑     i   =   0       M   -   1       ⁢           ⁢       X   i     ·     X   i         -         (       ∑     i   =   0       M   -   1       ⁢       X   i     ·     Y   t   i         )     2         ∑     i   =   0       M   -   1       ⁢       Y   t   i     ·     Y   t   i                     [   9   ]               (     Equation   ⁢           ⁢   10     )                           β   =         ∑     i   =   0       M   -   1       ⁢       X   i     ·     Y     t   MIN     i             ∑     i   =   0       M   -   1       ⁢       Y     t   MIN     i     ·     Y     t   MIN     i                   [   10   ]               
In equation 9 and 10, Y ti  is the t-th MDCT coefficients sample counting from the i-th sample of the index of MDCT coefficients Y; Y ti MIN  is the t MIN  MDCT coefficients sample counting from the i-th sample of the index of MDCT coefficients Y; D is the error between MDCT coefficients Y and MDCT coefficients X, as calculated by equation 9; M is the number of MDCT coefficients (e.g., the number of samples) to use to calculate the error D between Y ti  and X i . In addition, M is an integer equal to or greater than 2, t has a range from 0 to N−1 (i.e., similar to k as described in equation 3) and i has a range from 0 to M−1. Stated differently, according to equation 9, an error D is calculated error between MDCT coefficients Y ti  and X i  with respect to M samples (e.g., M samples may be taken from the beginning of a frame). The MDCT coefficients Y ti  varies by variable t in the calculation and D is calculated in accordance with the value of t. The minimum error (as calculated by D) between M samples is determined as t MIN —where Y itMIN  represents the t MIN -th MDCT coefficient samples among MDCT coefficients Y i . In equation 10, the t MIN -th MDCT coefficient samples are used to calculate gain β.
 
     Here,  FIG. 6A  and  FIG. 6B  conceptually show a similar-part search by a similar-part search section  501 .  FIG. 6A  shows an input signal spectrum, and shows the beginning part of the high band region (3.5 kHz to 7.0 kHz) of the input signal in a frame.  FIG. 6B  shows a situation in which a spectrum similar to the spectrum inside the frame shown in  FIG. 6A  is searched for sequentially from the beginning of the low band region of a decoded signal. 
     A similar-part search section  501  outputs MDCT coefficients X k  of the input signal, MDCT coefficients Y k  of the up-sampled low band component decoded signal, and calculated search result position t MIN  and gain β, to amplitude ratio adjusting section  502 . 
     Amplitude ratio adjusting section  502  extracts the part from search result position t MIN  to SR base /SR input ×(N−1) (if X k  becomes zero in the middle, the part up the position before X k  becomes zero), from MDCT coefficients Y k  of an up-sampled low band component decoded signal, and multiplies this part by gain β and designates the resulting value as copy source spectral data Z 1   k , expressed by equation 11.
 
(Equation 11)
 
 Z 1 k   =Y   k ·β ( k=t   MIN   , . . . , SR   base   /SR   input   ·N− 1)  [11]
 
     Next, amplitude ratio adjusting section  502  generates temporary spectral data Z 2   k  from copy source spectral data Z 1   k . To be more specific, amplitude ratio adjusting section  502  divides the length ((1−SR base /SR input )×N) of the spectral data of the high band component by the length (SR base /SR input ×N−1−t MIN ) of copy source spectral data Z 1   k , repeats copying the source spectral data Z 1   k  a number of times equaling the quotient such that source spectral data Z 1   k  continues from the part of k=SR base /SR input ×N−1 of temporary spectral data Z 2   k , and then copies copy source spectral data Z 1   k  for a number of samples equaling the samples of the remainder after dividing the length ((1−SR base /SR input )×N) of the spectral data of the high band component by the length (SR base /SR input ×N−1−t MIN ) of copy source spectral data Z 1   k , from the beginning of copy source spectral data Z 1   k , to the tail end of temporary spectral data Z 2   k . 
     Furthermore, suppose, when X k  becomes zero in the middle, amplitude ratio adjusting section  502  adds the length of the part where X k  is zero to the length ((1−SR base /SR input )×N) of the spectral data of the aforementioned high band component, and starts copying copy source spectral data Z 1   k  to temporary spectral data Z 2   k  from the part where X k  is zero in the middle. 
     Next, amplitude ratio adjusting section  502  adjusts the amplitude ratio of temporary spectral data Z 2   k . To be more specific, amplitude ratio adjusting section  502  divides MDCT coefficients X k  of the input signal and the high band component (k=SR base /SR input ×N, . . . , N−1) of temporary spectral data Z 2   k  into a plurality of bands first. 
     Here, a case where temporary spectral data Z 2   k  is copied from the part of k=SR base /SR input ×N in the aforementioned processing, will be explained. Amplitude ratio adjusting section  502  calculates amplitude ratio α j  for each band as expressed by equation 12 for MDCT coefficients X k  of the input signal and the high band component of temporary spectral data Z 2   k . In equation 12, suppose “NUM_BAND” is the number of bands and “band_index(j)” is the minimum sample index out of the indexes making up band j. 
     
       
         
           
             
               
                 
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                                 ⁢ 
                                 
                                   ( 
                                   j 
                                   ) 
                                 
                               
                             
                             
                               
                                 band_index 
                                 ⁢ 
                                 
                                   ( 
                                   
                                     j 
                                     + 
                                     1 
                                   
                                   ) 
                                 
                               
                               - 
                               1 
                             
                           
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             X 
                             k 
                           
                         
                         
                           
                             ∑ 
                             
                               k 
                               = 
                               
                                 band_index 
                                 ⁢ 
                                 
                                   ( 
                                   j 
                                   ) 
                                 
                               
                             
                             
                               
                                 band_index 
                                 ⁢ 
                                 
                                   ( 
                                   
                                     j 
                                     + 
                                     1 
                                   
                                   ) 
                                 
                               
                               - 
                               1 
                             
                           
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             Z 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               2 
                               k 
                             
                           
                         
                       
                     
                     ⁢ 
                     
                       ( 
                       
                         
                           j 
                           = 
                           0 
                         
                         , 
                         … 
                         ⁢ 
                         
                             
                         
                         , 
                         
                           NUM_BAND 
                           - 
                           1 
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   [ 
                   12 
                   ] 
                 
               
             
           
         
       
     
       FIG. 7  shows, conceptually, the processing in amplitude ratio adjusting section  502 .  FIG. 7  shows a situation in which the spectrum of the high band region is generated based on the similar-part searched from the low band region in  FIG. 6(   b ) (when NUM_BAND=5). 
     Amplitude ratio adjusting section  502  outputs amplitude ratio α j  for each band obtained from equation 12, search result position t MIN  and gain β to quantization section  503 . 
     Quantization section  503  quantizes amplitude ratio α j  for each band, search result position t MIN  and gain β outputted from amplitude ratio adjusting section  502  using codebooks provided in advance and outputs the index of each codebook, to encoded information integration section  207  as a high band component encoded information. 
     Here, suppose amplitude ratio α j  for each band, search result position t MIN  and gain β are quantized all separately and the selected codebook indexes are code_A, code_T and code_B, respectively. Furthermore, a quantization method is employed here whereby the code vector (or code) having the minimum distance (i.e. square error) to the quantization target is selected from the codebooks. However, this quantization method is in the public domain and will not be described in detail. 
       FIG. 8  is a block diagram showing an internal configuration of decoding apparatus  103  shown in  FIG. 1 . Encoded information division section  601  divides the low band component encoded information and the high band component encoded information from the inputted encoded information, outputs the divided low band component encoded information to low band decoding section  602 , and outputs the divided high band component encoded information to high band decoding section  605 . 
     Low band decoding section  602  decodes the low band component encoded information outputted from encoded information division section  601  using a CELP type speech decoding method, to generate a low band component decoded signal and outputs the low band component decoded signal generated to up-sampling processing section  603 . Since the configuration of low band decoding section  602  is the same as that of aforementioned low band decoding section  203 , its detailed explanations will be omitted. 
     Up-sampling processing section  603  up-samples the sampling frequency of the low band component decoded signal outputted from low band decoding section  602  from SR base  to SR input , and outputs the up-sampled low band component decoded signal to orthogonal transform processing section  604  as the up-sampled low band component decoded signal. 
     Orthogonal transform processing section  604  applies orthogonal transform processing (MDCT) to the up-sampled low band component decoded signal outputted from up-sampling processing section  603 , calculates MDCT coefficients Y′ k  of the up-sampled low band component decoded signal and outputs this MDCT coefficients Y′ k  to high band decoding section  605 . The configuration of orthogonal transform processing section  604  is the same as that of aforementioned orthogonal transform processing section  205 , and therefore detailed explanations thereof will be omitted. 
     High band decoding section  605  generates a signal including the high band component from MDCT coefficients Y′ k  of the up-sampled low band component decoded signal outputted from orthogonal transform processing section  604  and the high band component encoded information outputted from encoded information division section  601 , and makes this the output signal. 
     Next, an internal configuration of high band decoding section  605  shown in  FIG. 8  will be explained using  FIG. 9 . Dequantization section  701  dequantizes the high band component encoded information (i.e. code_A, code_T and code_B) outputted from encoded information division section  601  for the codebooks provided in advance, and outputs amplitude ratio α j  for each band produced, search result position t MIN  and gain β, to similar-part generation section  702 . To be more specific, the vectors and values indicated by the high band component encoded information (i.e. code_A, code_T and code_B) from each codebook are outputted to similar-part generation section  702  as amplitude ratio α j  for each band, search result position t MIN  and gain β, respectively. Here, suppose amplitude ratio α j  for each band, search result position t MIN  and gain β are dequantized using different codebooks as in the case of quantization section  503 . 
     Similar-part generation section  702  generates a high band component (k=SR base /SR input ×N, . . . , N−1) of MDCT coefficients Y′ from MDCT coefficients Y′ k  of the up-sampled low band component outputted from orthogonal transform processing section  604  and search position result t MIN  outputted from dequantization section  701  and gain β. To be more specific, copy source spectral data Z 1 ′ k  is generated according to equation 13.
 
(Equation 13)
 
 Z 1′ k   =Y′   k ·β ( k=t   MIN   , . . . , SR   base   /SR   input   ·N− 1)  [13]
 
     Furthermore, suppose, when Y′ k  is zero in the middle, copy source spectral data Z 1 ′ k  covers the part from the position where k is t MIN  up to the position before Y′ k  becomes zero, according to equation 13. 
     Next, similar-part generation section  702  generates temporary spectral data Z 2 ′ k  from copy source spectral data Z 1 ′ k  calculated according to equation 13. To be more specific, similar-part generation section  702  divides the length ((1−SR base /SR input )×N) of the spectral data of the high band component by the length (SR base /SR input ×N−1−t MIN ) of copy source spectral data Z 1 ′ k , repeats copying copy source spectral data Z 1 ′ k  a number of time equaling the quotient such that copy source spectral data Z 1 ′ k  continues from the part of k=SR base /SR input ×N−1 of temporary spectral data Z 2 ′ k , and then copies copy source spectral data Z 1 ′ k  for a number of samples equaling the samples of the remainder after dividing the length ((1−SR base /SR input )×N) of the spectral data of the high band component by the length (SR base /SR input ×N−1−t MIN ) of copy source spectral data Z 1 ′ k  from the beginning of copy source spectral data Z 1 ′ k  to the tail end of temporary spectral data Z 2 ′ k . 
     Furthermore, suppose, when Y′ k  becomes zero in the middle, similar-part generation section  702  adds the length of the part where Y′ k  is zero, to the length ((1−SR base /SR input )×N) of the spectral data of the aforementioned high band component, and starts copying copy source spectral data Z 1 ′ k  to temporary spectral data Z 2 ′ k  from the part where Y′ k  is zero in the middle. 
     Next, similar-part generation section  702  copies the value of the low band component of Y′ k  to the low band component of temporary spectral data Z 2 ′ k , expressed by equation 14. Here, a case where the temporary spectral data Z 2 ′ k  is copied from the part of k=SR base /SR input ×N in the aforementioned processing, will be explained.
 
(Equation 14)
 
Z2′ k =Y′ k ( k= 0 , . . . , SR   base   /SR   input   ·N− 1)  [14]
 
     Similar-part generation section  702  outputs the calculated temporary spectral data Z 2 ′ k  and amplitude ratio α j  per band, to amplitude ratio adjusting section  703 . 
     Amplitude ratio adjusting section  703  calculates temporary spectral data Z 3 ′ k  from temporary spectral data Z 2 ′ k  and amplitude ratio α j  for each band outputted from similar-part generation section  702 , expressed by equation 15. Here, α j  in equation 15 is the amplitude ratio of each band and band_index(j) is the minimum sample index in the indexes making up band j. 
     
       
         
           
             
               
                 
                   ( 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     15 
                   
                   ) 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     Z 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       3 
                       k 
                       ′ 
                     
                   
                   = 
                   
                     { 
                     
                       
                         
                           
                             Z 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               2 
                               k 
                               ′ 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               ( 
                               
                                 
                                   k 
                                   = 
                                   0 
                                 
                                 , 
                                 … 
                                 ⁢ 
                                 
                                     
                                 
                                 , 
                                 
                                   
                                     
                                       
                                         SR 
                                         base 
                                       
                                       / 
                                       
                                         SR 
                                         input 
                                       
                                     
                                     · 
                                     N 
                                   
                                   - 
                                   1 
                                 
                               
                               ) 
                             
                           
                         
                       
                       
                         
                           
                             Z 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               
                                 2 
                                 k 
                                 ′ 
                               
                               · 
                               
                                 
                                   α 
                                   j 
                                 
                                 ( 
                                 
                                   
                                     k 
                                     = 
                                     
                                       
                                         
                                           SR 
                                           base 
                                         
                                         / 
                                         
                                           SR 
                                           input 
                                         
                                       
                                       · 
                                       N 
                                     
                                   
                                   , 
                                   … 
                                   ⁢ 
                                   
                                       
                                   
                                   , 
                                   
                                     N 
                                     - 
                                     
                                       1 
                                       ⁢ 
                                       
                                         : 
                                       
                                     
                                   
                                 
                               
                             
                           
                         
                       
                       
                         
                           
                             
                               
                                 band_index 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 
                                   ( 
                                   j 
                                   ) 
                                 
                               
                               ≤ 
                               k 
                               &lt; 
                               
                                 band_index 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 
                                   ( 
                                   
                                     j 
                                     + 
                                     1 
                                   
                                   ) 
                                 
                               
                             
                             ) 
                           
                         
                       
                       
                         
                           
                             ( 
                             
                               
                                 j 
                                 = 
                                 0 
                               
                               , 
                               … 
                               ⁢ 
                               
                                   
                               
                               , 
                               
                                 NUM_BAND 
                                 - 
                                 1 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   15 
                   ] 
                 
               
             
           
         
       
     
     Amplitude ratio adjusting section  703  outputs temporary spectral data Z 3 ′ k  calculated according to equation 15 to orthogonal transform processing section  704 . 
     Orthogonal transform processing section  704  contains buffer buf′ k  and is initialized according to equation 16.
 
(Equation 16)
 
 buf′   k =0 ( k =0, . . . , N−1)  [16]
 
     Orthogonal transform processing section  704  calculates decoded signal Y″ n  using temporary spectral data Z 3 ′ k  outputted from amplitude ratio adjusting section  703 , according to equation 17. 
     
       
         
           
             
               
                 
                   ( 
                   
                     Equation 
                     ⁢ 
                     
                       
                           
                       
                       ⁢ 
                       
                           
                       
                     
                     ⁢ 
                     17 
                   
                   ) 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     Y 
                     n 
                     ″ 
                   
                   = 
                   
                     
                       2 
                       N 
                     
                     ⁢ 
                     
                       
                         ∑ 
                         
                           n 
                           = 
                           0 
                         
                         
                           
                             2 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             N 
                           
                           - 
                           1 
                         
                       
                       ⁢ 
                       
                         Z 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           3 
                           k 
                           ″ 
                         
                         ⁢ 
                         
                           cos 
                           ⁡ 
                           
                             [ 
                             
                               
                                 
                                   
                                     
                                       ( 
                                       
                                         
                                           2 
                                           ⁢ 
                                           
                                               
                                           
                                           ⁢ 
                                           n 
                                         
                                         + 
                                         1 
                                         + 
                                         N 
                                       
                                       ) 
                                     
                                   
                                 
                                 
                                   
                                     
                                       
                                         ( 
                                         
                                           
                                             2 
                                             ⁢ 
                                             
                                                 
                                             
                                             ⁢ 
                                             k 
                                           
                                           + 
                                           1 
                                         
                                         ) 
                                       
                                       ⁢ 
                                       
                                           
                                       
                                       ⁢ 
                                       π 
                                     
                                   
                                 
                               
                               
                                 4 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 N 
                               
                             
                             ] 
                           
                         
                         ⁢ 
                         
                           ( 
                           
                             
                               n 
                               = 
                               0 
                             
                             , 
                             … 
                             ⁢ 
                             
                                 
                             
                             , 
                             
                               N 
                               - 
                               1 
                             
                           
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   17 
                   ] 
                 
               
             
           
         
       
     
     Here, Z 3 ″ k  is a vector combining temporary spectral data Z 3 ′ k  and buffer buf′ k  and is calculated according to equation 18. 
     
       
         
           
             
               
                 
                   ( 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     18 
                   
                   ) 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     Z 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       3 
                       k 
                       ′ 
                     
                   
                   = 
                   
                     { 
                     
                       
                         
                           
                             buf 
                             k 
                             ′ 
                           
                         
                         
                           
                             ( 
                             
                               
                                 k 
                                 = 
                                 0 
                               
                               , 
                               
                                 
                                   … 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   N 
                                 
                                 - 
                                 1 
                               
                             
                             ) 
                           
                         
                       
                       
                         
                           
                             Z 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               3 
                               k 
                               ′ 
                             
                           
                         
                         
                           
                             ( 
                             
                               
                                 k 
                                 = 
                                 N 
                               
                               , 
                               
                                 
                                   … 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   2 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   N 
                                 
                                 - 
                                 1 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   18 
                   ] 
                 
               
             
           
         
       
     
     Next, orthogonal transform processing section  704  updates buffer buf′ k  according to equation 19.
 
(Equation 19)
 
 buf′   k =Z3′ k  ( k= 0, . . . , N−1)  [19]
 
     Orthogonal transform processing section  704  obtains decoded signal Y″ n  as an output signal. 
     In this way, in accordance with Embodiment 1, to generate spectral data of the high band region of a signal to be encoded based on spectral data of the low band region of the signal, a similar-part search is performed for a part (e.g. beginning part) in the spectral data of the high band region, in the quantized low band region, and spectral data of the high band region is generated based on the search result, so that it is possible to encode spectral data of the high band region of a wideband signal based on spectral data of the low band region with an extremely small amount of information and amount of calculation processing, and, furthermore, obtain a decoded signal of high quality even when a significant quantization distortion occurs in the spectral data of the low band region. 
     Embodiment 2 
     Embodiment 1 has explained a method of performing a similar-part search with respect to MDCT coefficients of up-sampled low band component decoded signal, and the beginning part of high band components of MDCT coefficients of an input signal, and calculating parameters for generating MDCT coefficients for the high band component at the time of decoding. Now, with embodiment 2, a weighted similar-part search method will be described, whereby, in high band components of the MDCT coefficients of an input signal, lower band components are regarded more important. 
     Since the communication system according to Embodiment 2 is similar to the configuration of Embodiment 1 shown in  FIG. 1 ,  FIG. 1  will be used, and furthermore, since the encoding apparatus according to Embodiment 2 of the present invention is similar to the configuration of Embodiment 1 shown in  FIG. 2 ,  FIG. 2  will be used and overlapping explanations will be omitted. However, in the configuration shown in  FIG. 2 , high band encoding section  206  has a function different from that in Embodiment 1, and therefore high band encoding section  206  will be explained using  FIG. 5 . 
     Similar-part search section  501  calculates a search result position t MIN  (t=t MIN ) when error D 2  between MDCT coefficients Y k  of an up-sampled low band component decoded signal outputted from orthogonal transform processing section  205  and M (M is an integer equal to or greater than 2) samples from the beginning of MDCT coefficients X k  of the input signal outputted from orthogonal transform processing section  205  becomes a minimum, and gain β 2  at that moment. Error D 2  and β 2  are calculated according to equation 20 and equation 21, respectively. 
     
       
         
           
             
               
                 
                   ( 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     20 
                   
                   ) 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     D 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                   = 
                   
                     
                       ( 
                       
                         
                           
                             ∑ 
                             
                               i 
                               = 
                               0 
                             
                             
                               M 
                               - 
                               1 
                             
                           
                           ⁢ 
                           
                             
                               X 
                               i 
                             
                             · 
                             
                               X 
                               i 
                             
                           
                         
                         - 
                         
                           
                             
                               ( 
                               
                                 
                                   ∑ 
                                   
                                     i 
                                     = 
                                     0 
                                   
                                   
                                     M 
                                     - 
                                     1 
                                   
                                 
                                 ⁢ 
                                 
                                   
                                     X 
                                     i 
                                   
                                   · 
                                   
                                     Y 
                                     t 
                                     i 
                                   
                                 
                               
                               ) 
                             
                             2 
                           
                           
                             
                               ∑ 
                               
                                 i 
                                 = 
                                 0 
                               
                               
                                 M 
                                 - 
                                 1 
                               
                             
                             ⁢ 
                             
                               
                                 Y 
                                 t 
                                 i 
                               
                               · 
                               
                                 Y 
                                 t 
                                 i 
                               
                             
                           
                         
                       
                       ) 
                     
                     · 
                     
                       W 
                       i 
                     
                   
                 
               
               
                 
                   [ 
                   20 
                   ] 
                 
               
             
             
               
                 
                   ( 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     21 
                   
                   ) 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     β 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                   = 
                   
                     
                       
                         ∑ 
                         
                           i 
                           = 
                           0 
                         
                         
                           M 
                           - 
                           1 
                         
                       
                       ⁢ 
                       
                         
                           X 
                           i 
                         
                         · 
                         
                           Y 
                           
                             t 
                             MIN 
                           
                           i 
                         
                       
                     
                     
                       
                         ∑ 
                         
                           i 
                           = 
                           0 
                         
                         
                           M 
                           - 
                           1 
                         
                       
                       ⁢ 
                       
                         
                           Y 
                           
                             t 
                             MIN 
                           
                           i 
                         
                         · 
                         
                           Y 
                           
                             t 
                             MIN 
                           
                           i 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   21 
                   ] 
                 
               
             
           
         
       
     
     Here, W i  in equation 20 is a weight having a value of about 0.0 to 1.0, and is multiplied when error D 2  (i.e. distance) is calculated. To be more specific, a smaller error sample index (that is, an MDCT coefficients of a lower band region), is assigned a greater weight. An example of W i  is shown in equation 22. 
     
       
         
           
             
               
                 
                   ( 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     22 
                   
                   ) 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     W 
                     i 
                   
                   = 
                   
                     
                       
                         - 
                         
                           0.5 
                           
                             M 
                             - 
                             1 
                           
                         
                       
                       ⁢ 
                       i 
                     
                     + 
                     
                       1.0 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         ( 
                         
                           
                             i 
                             = 
                             0 
                           
                           , 
                           … 
                           ⁢ 
                           
                               
                           
                           , 
                           
                             M 
                             - 
                             1 
                           
                           , 
                           
                             M 
                             ≥ 
                             2 
                           
                         
                         ⁢ 
                         
                             
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   [ 
                   22 
                   ] 
                 
               
             
           
         
       
     
     In this way, by calculating the distance using a greater weight for MDCT coefficients of lower band, it is possible to realize a search placing the emphasis on the distortion in the part connecting the low band component and the high band component. 
     The configurations of amplitude ratio adjusting section  502  and quantization section  503  are the same as those for the processing explained in Embodiment 1, and therefore detailed explanations thereof will be omitted. 
     Encoding apparatus  101  has been explained so far. The configuration of decoding apparatus  103  is the same as explained in Embodiment 1, and therefore detailed explanations thereof will be omitted. 
     In this way, in accordance with Embodiment 2, to generate spectral data of the high band region of a signal to be encoded based on spectral data of the low band region of the signal, the distance is calculated by assigning greater weights to smaller error sample indexes, a similar-part search for part (i.e. beginning part) of spectral data of the high band region is performed in spectral data of the quantized low band region and spectral data of the high band region is generated based on the result of the search, so that it is possible to encode spectral data of the high band region of a wideband signal in high perceptual quality based on spectral data of the low band region of the signal and furthermore obtain a decoded signal of high quality even when a significant quantization distortion occurs in the spectral data of the low band region. 
     The present embodiment has explained a case where, to generate spectral data of the high band region of a signal to be encoded based on spectral data of the low band region of the signal, a similar-part search for a part (i.e. beginning part) of the spectral data of the high band region is performed in the spectral data of the quantized low band region, so that the present invention is not limited to this and it is equally possible to adopt the above-described weighting in distance calculation for the entire part of the spectral data of the high band region. 
     Furthermore, although the present embodiment has explained a method of generating spectral data of the high band region of a signal to be encoded is generated based on spectral data of the low band region of the signal, by calculating the distance by assigning greater weights to smaller error sample indexes, performing a similar-part search for a part (i.e. beginning part) of the spectral data of the high band region in spectral data of the quantized low band region, and generating spectral data of the high band region based on the result of the search, but the present invention is by no means limited to this and may likewise adopt a method of introducing the length of copy source spectral data as an evaluation measure during a search. To be more specific, by making a search result that increases the length of the copy source spectral data, that is, by making an entry of a search position of a low band more likely to be selected, it is possible to further improve the quality of an output signal by reducing the number of discontinuous parts caused when the spectral data of the high band region is copied a plurality of times and placing the discontinuous parts in high frequency bands. 
     The above-described embodiments have explained that the index of the MDCT coefficients of the spectral data of the high band region generated starts from SR base /SR input ×(N−1), but the present invention is not limited to this, and the present invention is also applicable to cases where spectral data of the high band region is generated likewise from a part where low band spectral data becomes zero, irrespective of sampling frequencies. Furthermore, the present invention is also applicable to a case where spectral data of the high band region is generated from an index specified from the user and system side. 
     The above-described embodiments have explained the CELP type speech encoding scheme in the low band encoding section as an example, but the present invention is not limited to this and is also applicable to cases where a down-sampled input signal is coded according to a speech/sound encoding scheme other than CELP type. The same applies to the low band decoding section. 
     The present invention is further applicable to a case where a signal processing program is recorded or written into a mechanically readable recording medium such as a memory, disk, tape, CD, DVD and operated, and operations and effects similar to those of the present embodiment can be obtained. 
     Each function block employed in the description of each of the aforementioned embodiments may typically be implemented as an LSI constituted by an integrated circuit. These may be individual chips or partially or totally contained on a single chip. 
     “LSI” is adopted here but this may also be referred to as “IC”, “system LSI”, “super LSI”, or “ultra LSI” depending on differing extents of integration. 
     Further, the method of circuit integration is not limited to LSI&#39;s, and implementation using dedicated circuitry or general purpose processors is also possible. After LSI manufacture, utilization of an FPGA (Field Programmable Gate Array) or a reconfigurable processor where connections and settings of circuit cells within an LSI can be reconfigured is also possible. 
     Further, if integrated circuit technology comes out to replace LSI&#39;s as a result of the advancement of semiconductor technology or a derivative other technology, it is naturally also possible to carry out function block integration using this technology. Application of biotechnology is also possible. 
     The disclosures of Japanese Patent Application No. 2006-131852, filed on May 10, 2006, and Japanese Patent Application No. 2007-047931, filed on Feb. 27, 2007, including the specifications, drawings and abstracts, are incorporated herein by reference in their entirety. 
     INDUSTRIAL APPLICABILITY 
     The encoding apparatus and encoding method according to the present invention make it possible to encode spectral data of the high band region of a wideband signal based on spectral data of the low band region of the signal and produce a decoded signal of high quality even when a significant quantization distortion occurs in the spectral data of the low band region, and are therefore applicable for use in, for example, a packet communication system and mobile communication system.