Patent Publication Number: US-7596492-B2

Title: Apparatus and method for concealing highband error in split-band wideband voice codec and decoding

Description:
FIELD OF THE INVENTION 
   The present invention relates to an apparatus and method for restoring a packet loss and a frame error in a spilt-band voice codec and a decoding system using the same; and, in particular, to an apparatus for restoring a voice corresponding to highband in a spilt-band wideband voice codec when an error packet or a lost packet are occurred. 
   DESCRIPTION OF RELATED ART 
   A technology for transmitting an analog voice as a digital streaming is generally used in not only a conventional public switched telephone network (PSTN) but a wireless network and a voice over internet protocol (VOIP) network getting popular in recent. If a voice is simply sampled and digitalized, for example, sampled in 8 kHz and coded in an 8 bit per sample, 64 kbit/s is required. However, if a proper voice analysis and coding scheme are used in voice compression, the transmission rate of the voice can be decreased. 
   As mentioned above, a voice codec is an apparatus for compressing a voice to a digital bit stream and expanding a digital bit stream to a voice. Currently, most conventional voice codecs are narrowband codec, and used for encoding and decoding a voice ranging from 300 Hz to 3,400 Hz. However, for providing better voice quality than that of the conventional narrowband voice codec, a wideband voice codec encoding and decoding the voice signal ranging from 50 Hz to 7000 Hz becomes prominent. Over the past few years, wideband voice codecs were standardized by International Telecommunication Union-Telecommunication (ITU-T), 3rd Generation Partnership Project (3GPP), 3rd Generation Partnership Project 2 (3GPP2), etc. A spilt-band wideband voice codec is one type of the wideband voice codecs, splits the overall bandwidth ranging from 50 Hz to 7,000 Hz of the voice signal into two bands as lowband and highband, and encodes each band separately. This type of voice codec can adopt different coding schemes for each band, e.g., Code-Excited Linear Prediction (CELP) coding for lowband and Transform coding for highband. 
     FIG. 1  is a block diagram illustrating a conventional spilt-band voice codec system. 
   As shown, in a transmitting part, an input voice signal  100  sampled in 16 kHz is split into a lowband voice signal and a highband voice signal which have the same sampling frequency as the input voice signal  100  by passing the input voice signal  100  through a low pass filter (LPF)  111  and a high pass filter (HPF)  121  respectively. A 16 kHz lowband voice signal is converted into an 8 kHz lowband voice signal by a down-sampler  112  and a 16 kHz highband voice signal is also converted into an 8 kHz highband voice signal by a down-sampler  122  in the same way. The 8 kHz lowband voice signal is encoded to a lowband bit stream by a lowband encoder  113  and the 8 kHz highband voice signal is encoded to a highband bit stream by a highband encoder  123 . The lowband bit stream and the highband bit stream are multiplexed into a wideband bit stream by a multiplexer  150  and the wideband bit stream  101  is transmitted through a channel  160 . 
   In the receiving part, the wideband bit stream  102  transmitted through the channel  160  is demultiplexed into a lowband bit stream and a highband bit stream by a demultiplexer  170 . The lowband bit stream is decoded to a 8 kHz lowband voice signal by a lowband decoder  131  and the highband bit stream is decoded to a 8 kHz highband voice signal by a highband decoder  141 . The 8 kHz lowband voice signal is converted into a 16 kHz lowband voice signal by an up-sampler  132  and the 8 kHz highband voice signal is converted into a 16 kHz voice signal by an up-sampler  142 . A highband component of the 16 kHz lowband voice signal is removed by a LPF  133  and a lowband component of the 16 kHz highband voice signal by a HPF  143 . Finally, the 16 kHz lowband and highband voice signals are combined by a combiner  180  thereby a synthesized voice signal  103  is generated. 
   The spilt-band wideband voice codec can adopt different coding scheme (e.g., Pulse Coded Modulation (PCM), CELP coding, Transform coding, etc) for each band independently. For example, a spilt-band wideband voice codec can use the CELP for the lowband and the transform coding for the highband. 
   Most of the conventional voice codecs adopt a packet loss concealment algorithm or a frame erasure concealment algorithm so that copes with the packet loss and the frame error. 
   However, these algorithms can be mostly applied to the narrowband voice codecs and depend on adopted voice encoding method. As mentioned above, the spilt-band wideband voice codec generally adopts different voice coding methods for the lowband and the highband. Therefore, the codec has a drawback of designing an additional error concealment method according to the adopted highband coding method. 
   SUMMARY OF THE INVENTION 
   It is, therefore, an object of the present invention to provide an apparatus and method for concealing a packet loss and a frame error in a highband of a spilt-band wideband voice codec so that provides a high quality voice communication and a bit stream decoding system using the same. 
   In accordance with an aspect of the present invention, there is provided an apparatus for concealing a highband error in a spilt-band wideband voice codec, the apparatus including: a lowband LPC coefficient extracting unit for extracting a lowband linear predictive coding (LPC) coefficient from a lowband voice signal passed by a lowband decoding unit; a highband excitation signal generating unit for generating a highband excitation signal based on the lowband voice signal and the lowband LPC coefficient; a highband LPC coefficient generating unit for generating a highband LPC coefficient based on the lowband LPC coefficient; a highband voice synthesizing unit for synthesizing a highband voice signal based on the highband excitation signal and the highband LPC coefficient; and a high pass filtering unit for removing a lowband component of the synthesized highband voice signal by the highband voice synthesizing unit and generating the synthesized highband voice signal. 
   In accordance with another aspect of the present invention, there is provided a method for concealing a highband error in spilt-band wideband voice codec, the method including the steps of: extracting a lowband linear predictive coding (LPC) coefficient from a lowband voice signal transmitted from a lowband decoding unit; generating a highband excitation signal based on the lowband voice signal and the lowband LPC coefficient; generating a highband LPC coefficient based on the lowband LPC coefficient; synthesizing a highband voice signal based on the highband excitation signal and the highband LPC coefficient; and removing a lowband component of the synthesized highband voice signal passed by the highband voice synthesizing unit and outputting the synthesized highband voice signal. 
   In accordance with still another aspect of the present invention, there is provided a bit stream decoding system using an apparatus for concealing a highband error, the system including: a packet loss detecting unit for detecting a packet loss of an input bit stream; a demultiplexing unit for demultiplexing the input bit stream into a highband bit stream and a lowband bit stream by analyzing the input stream for every frame; a lowband decoding unit for decoding the lowband bit stream passed from the demultiplexing unit into a lowband voice signal; a highband error detecting unit for detecting a highband error by checking the highband bit stream passed from the demultiplexing unit and determining whether the input bit stream has a error; a first selecting unit for selecting an apparatus to decode the highband bit stream based on outputs of the packet loss detecting unit and the highband error detecting unit; a highband error concealing unit for concealing an error in a highband frame or lost frame; a second selecting unit for selecting an apparatus to output a synthesized highband voice based on the outputs of the packet loss detecting unit and the highband error detecting unit; and a combining unit for outputting a synthesized wideband voice signal by combining the synthesized lowband voice signal and the synthesized highband voice signal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a block diagram showing a conventional spilt-band voice codec system; 
       FIG. 2  is a block diagram illustrating a bit stream decoding system using an apparatus for concealing a highband error in the spilt-band wideband voice codec in accordance with a preferred embodiment of the present invention; 
       FIG. 3  is a block diagram describing an apparatus for concealing a highband error in the spilt-band wideband voice codec in accordance with a preferred embodiment of the present invention; 
       FIGS. 4A and 4B  are block diagrams showing an highband excitation signal generator of the apparatus for concealing a highband error in accordance with a preferred embodiment of the present invention; and 
       FIG. 5  is a block diagram showing a highband LPC coefficient generator of the apparatus for concealing a highband error in accordance with a preferred embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Herein after, an apparatus for concealing highband error in spilt-band wideband voice codec and a method thereof will be described in detail with reference to the accompanying drawings. 
     FIG. 2  is a block diagram illustrating a bit stream decoding system using an apparatus for concealing a highband error in the spilt-band wideband voice codec in accordance with a preferred embodiment of the present invention. 
   As shown, the bit stream decoding system includes a packet loss detecting block  210 , a demultiplexing block  220 , a lowband decoding block  230 , a highband decoding block  240  and a combiner  250 . 
   The packet loss detecting block  210  detect whether the packet transmitted over the channel is lost or not. The packet loss detecting block  210  generates a Bad Frame Indicator for the Packet Loss (BFI_PL)  260 A signal based on the detecting result. The demultiplexing block  220  receives the input bit stream  200  and demultiplexes the input stream  200  into a lowband bit stream  201  and a highband bit stream  202  by analyzing the input stream  200  on a frame by frame basis. The lowband decoding block  230  receives the lowband bit stream  201  and the BFI_PL  260 A, and then decodes lowband bit stream into a lowband voice signal  206  or conceals lost and erroneous lowband frames thereby generates a synthesized lowband voice signal  203  and transmits the lowband voice signal  206  to a highband error concealer  247  of the highband decoding block  240 . The highband decoding block  240  receives the highband bit stream  202 , the BFI_PL  260 A and the synthesized lowband voice signal  206 , and then decodes the highband bit stream  202  into a highband voice signal or conceals lost and erroneous highband frames thereby generates a synthesized highband voice signal  204 . 
   The combiner  250  generates a synthesized wideband voice signal  205  by combining the synthesized lowband voice signal  203  and the synthesized highband voice signal  204 . 
   As shown, the packet loss detecting block  210  determines whether a packet is lost or not according to a state of the packet during a transmission of the packet. If the packet loss is occurred, the packet loss detecting block  210  sets a bad frame indicator for the packet loss signal (BFI_PL)  260 A to 1. If the packet loss doesn&#39;t occur, the packet loss detecting block  210  sets BFI_PL  260 A to 0. 
   The lowband decoding block  230  includes a lowband error detector  231 , a first switch  232 , a lowband decoder  233 , a lowband error concealer  237 , a second switch  234 , an up-sampler  235  and a low pass filter  236 . 
   The lowband error detector  231  determines whether an error is occurred in the lowband bit stream  201  or not by analyzing the lowband bit stream  201 . Conventionally, the analysis procedure is done by checking the Cyclic Redundancy Code CRC). If there is an error in the lowband bit stream  201 , the lowband bit stream detector  231  sets a bad frame indicator for lowband error signal (BFI_LE)  260 B to 1. If there is no error, the lowband bit stream detector  231  sets the BFI_BE  260 B to 0. 
   The first switch  232  operates based on values of the BFI_PL  260 A and the BFI_LE  260 B. If both of them are 0, i.e., there is no lowband error frame and no packet loss of the input bit stream  200 , the first switch  232  transmits the lowband bit stream  201  to the lowband decoder  232  and enables the lowband decoder  231 . Otherwise, i.e., if there is a lowband error frame or a packet loss of the input bit stream  200 , the first switch  232  enables the lowband error concealer  237 . 
   The lowband decoder  233  decodes the lowband bit stream  201  into a lowband voice signal  206  based on a predetermined decoding method and transmits the lowband voice signal  206  to a third switch  242  of the highband decoding block  240  for concealing the highband error of the input bit stream  200 . 
   The lowband error concealer  237  recovers the lowband voice signal  206  for the erroneous frame or lost frame using information stored from the previous frame. The lowband error concealer  237  transmits the restored lowband voice signal  206  to the third switch  242  of the highband decoding block  240  for concealing the highband error of the input bit stream  200 . 
   The second switch  234  selects one of the lowband voice signal  206  from the lowband decoder  233  and the restored lowband voice signal  206  from the lowband error concealer  237  based on the BFI_PL  260 A and the BFI_LE  260 B in the same switching manner of the first switch  232 . If both of the BFI_PL  260 A and the BFI_LE  260  B are 0, the second switch  234  transmits the lowband voice signal  203  to the up-sampler  235 . Otherwise, the second switch  234  transmits the restored lowband voice signal to the up-sampler  235 . 
   The up-sampler  235  receives the lowband voice signal  206  from the lowband decoder  233  or the lowband error concealer  237  and converts the sampling rate of the lowband voice signal from 8 kHz into 16 kHz. 
   The low pass filter  235  receives the 16 kHz lowband voice signal, removes an unnecessary highband component of the 16 kHz lowband voice signal and generates the synthesized lowband voice signal  203 . 
   The highband decoding block  240  includes a highband error detector  241 , a third switch  242 , a highband decoder  243 , a forth switch  244 , a second up-sampler  245 , a high pass filter  246  and a highband error concealer  247 . 
   The highband error detector  241  determines whether an error is occurred in the highband bit stream  202  or not by analyzing the highband bit stream  202 . This is usually done by the CRC check. If there is an error in the highband bit stream  202 , the highband bit stream detector  241  sets a bad frame indicator for highband error signal (BFI_HE)  260 C to 1. If there is no error, the highband error detector  241  sets BFI_HE  260 C to 0. 
   The third switch  242  selects block to be enabled based on the values of the BFI_PL  260 A and the BFI_HE  260 C. If both of them are 0, i.e., there is no highband error frame and no packet loss of the input bit stream  200 , the third switch  243  enables the highband decoder  242 . Otherwise, i.e., there is a highband error frame or a packet loss of the input bit stream  200 , the third switch  243  enables the highband error concealer  247 . 
   The highband error concealer  247  receives the lowband voice signal  206  from the lowband decoder  233  or the lowband error concealer  237 , recovers the highband voice signal from the lowband voice signal  206  and transmits the synthesized highband signal to the forth switch  244 . 
   The highband decoder  243  decodes the highband bit stream  202  into a highband voice signal based on the predetermined decoding method. 
   The second up-sampler  245  converts the sampling rate of the highband voice signal from 8 kHz into 16 kHz. 
   The high pass filter  246  removes an unnecessary lowband component of the 16 kHz highband voice signal and transmits the filtered highband voice signal to the forth switch  244 . 
   The forth switch  244  selects one of the restored highband voice signal of the highband error concealer  247  and the filtered highband voice signal of the high pass filter  246  based on the BFI_PL  260 A and the BFI_HE  260 C. If the BFI_PL  260 A and the BFI_HE  260 C are 0, the forth switch  244  transmits the filtered 16 kHz highband voice signal as the synthesized highband voice signal  204  to the combiner  250 . Otherwise, the forth switch  244  transmits the restored highband voice signal as the synthesized highband voice signal  204  to the combiner  250 . 
     FIG. 3  is a block diagram describing an apparatus for concealing a highband error in the spilt-band wideband voice codec in accordance with a preferred embodiment of the present invention. 
   As shown, the apparatus includes a lowband LPC coefficient extractor  360 , a highband LPC coefficient generator  330 , a highband excitation signal generator  320 , a LPC synthesizing filter  340  and a high pass filter  350 . 
   The lowband LPC coefficient extractor  360  extracts a lowband linear predictive coding (LPC) coefficient  311  from the lowband voice signal  206  transmitted from the lowband decoding block  230 . The highband LPC coefficient generator  330  receives the lowband LPC coefficient  311  and generates a highband LPC coefficient  312 , and then transmits the highband LPC coefficients to the LPC synthesis filter  340 . The highband excitation signal generator  320  receives the lowband voice signal  206  and the lowband LPC coefficient  311  and generates a 16 kHz highband excitation signal. The LPC synthesizing filter  340  receives the highband excitation signal and the highband LPC coefficient  312  and synthesizes a highband voice signal, and then transmits a synthesized highband voice signal to the high pass filter  350 . The high pass filter  350  removes an unnecessary lowband component of the synthesized highband voice signal and generates the synthesized highband voice signal  313 . 
   The LPC synthesizing filter  340  is generally expressed in Eq. 1 as below. 
   
     
       
         
           
             
               
                 
                   A 
                   ⁡ 
                   
                     ( 
                     z 
                     ) 
                   
                 
                 = 
                 
                   1 
                   
                     1 
                     + 
                     
                       
                         ∑ 
                         
                           i 
                           = 
                           1 
                         
                         p 
                       
                       ⁢ 
                       
                         
                           a 
                           i 
                         
                         ⁢ 
                         
                           z 
                           
                             - 
                             i 
                           
                         
                       
                     
                   
                 
               
             
             
               
                 Eq 
                 . 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
   
   Wherein α i  is an ith highband LPC coefficient and p is a LPC order. 
     FIGS. 4A and 4B  are block diagrams showing examples of the highband excitation signal generator  320  of the apparatus for concealing a highband error in accordance with a preferred embodiment of the present invention. The drawings illustrate processes of a spectral folding method and a nonlinear distortion method respectively for generating the highband excitation signal  402  from the lowband voice signal  206  by the highband excitation signal generator  320 . 
   Herein, both of the two methods are based on the fact that the highband of a voice is highly correlated to the lowband. Figures located between blocks describe a typical spectral form of each signal and a horizontal axis (f) means a frequency. 
     FIG. 4A  shows the highband excitation signal generator  320  using the spectral folding method. The highband excitation signal generator  320  includes a LPC analysis filter  410 , an up-sampler  420  and a high pass filer  430 . 
   The LPC analysis filter  410  is operated based on the lowband LPC coefficients  311 , generates an 8 kHz lowband excitation signal from the 8 kHz lowband voice signal  206  and is an inverse-filter of Eq. 1 as expressed as below. 
   
     
       
         
           
             
               
                 
                   B 
                   ⁡ 
                   
                     ( 
                     z 
                     ) 
                   
                 
                 = 
                 
                   1 
                   + 
                   
                     
                       ∑ 
                       
                         i 
                         = 
                         1 
                       
                       p 
                     
                     ⁢ 
                     
                       
                         b 
                         i 
                       
                       ⁢ 
                       
                         z 
                         
                           - 
                           i 
                         
                       
                     
                   
                 
               
             
             
               
                 Eq 
                 . 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
   
   Wherein b i  is an ith lowband LPC coefficient and p is a LPC order. 
   The spectrum of the 8 kHz lowband excitation signal has a flat shape in a frequency domain due to whitening process of the LPC analysis filter  410 . 
   The up-sampler  420  increases the sampling frequency of the lowband excitation signal from 8 kHz to 16 kHz. Consequently, the up-sampler  420  creates the mirror image folded at 4 kHz of the lowband spectrum in highband. 
   Finally, the high pass filter  430  removes an unnecessary lowband component of the up-sampled excitation signal and generates a highband excitation signal  402 . 
     FIG. 4B  is the highband excitation signal generator  320  using the nonlinear distortion method. The highband excitation signal generator  320  includes a LPC analysis filter  440 , an up-sampler  450 , a low pass filter  460 , a nonlinear distorter  470  and a high pass filter  480 . 
   The LPC analysis filter  440  is constructed using the lowband LPC coefficients  311 , generates a 8 kHz lowband excitation signal from the 8 kHz lowband voice signal  206  and is expressed as Eq. 2. The spectrum of the 8 kHz lowband excitation signal has a flat shape in a frequency domain. 
   The up-sampler  450  increases the sampling frequency of the lowband excitation signal from 8 kHz to 16 kHz. 
   The low pass filter  460  removes a highband component of the up-sampled excitation signal and generates a filtered lowband excitation signal. 
   The nonlinear distorter  470  adds a highband component to the filtered lowband excitation signal using the nonlinear functions like a square function or an absolute function, and generates a distorted excitation signal which is in phase with the lowband excitation signal and conserves a harmonic structure of the lowband excitation signal without a spectral distortion. 
   The high pass filter  480  removes a lowband component from the distorted excitation signal and generates a highband excitation signal  405 . 
     FIG. 5  is a block diagram showing a highband LPC coefficient generator  330  of the apparatus for concealing a highband error in accordance with an embodiment of the present invention and illustrating a process for extrapolating a highband LPC coefficient  502  from the lowband LPC coefficient  311 . 
   As shown, the highband LPC coefficient generator  330  includes a type converter A  510 , a lowband codebook searcher  520 , a highband codebook searcher  530 , a type converter B  540 , a lowband codebook  567 , and a highband codebook  577 . 
   The type converter A  510  converts the type of the lowband coefficients  311  from LPC to line spectral pair (LSP). The LSP is more convenient type for searching a codeword in a codebook. The lowband codebook searcher  520  searches a most similar codeword vector to the lowband LSP coefficients vector in the lowband codebook  567  and outputs its codeword index as a searched one. The highband codebook searcher  530  searches a highband LSP codeword corresponding to the searched index in a lowband codebook  577 . The type converter B  540  converts the highband LSP codeword searched by the highband codebook searcher  530  into highband LPC coefficients  502 . The lowband codebook  567  stores lowband LSP codeword vectors trained by the codebook training block  590 . The highband codebook  577  stores highband LSP codeword vectors trained by the codebook training block  590 . The codebook training block  590  trains the lowband LSP coefficient vectors and the highband LSP coefficient vectors simultaneously. 
   The detail operation of the highband LPC coefficient generator  330  will be described hereinafter. 
   The type converter A  510  converts the lowband LPC coefficient  311  into the same type of the codeword in the codebook. The LSP is used as a codeword in this embodiment and the type converter  510  converts the lowband LPC coefficient  311  into a lowband LSP coefficient. 
   The lowband codebook searcher  520  searches the nearest codeword with the converted lowband LSP coefficient in the lowband codebook  567  and outputs an index of the codeword. The method for searching a codebook is based on a distance measurement as Eq. 3 and selects a codeword having nearest distance value among all codewords existing in the codebook. 
   
     
       
         
           
             
               
                 index 
                 = 
                 
                   
                     
                       arg 
                       cw 
                     
                     ⁢ 
                     max 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       D 
                       ⁡ 
                       
                         ( 
                         
                           
                             l 
                             in 
                           
                           , 
                           
                             l 
                             cw 
                           
                         
                         ) 
                       
                     
                   
                   = 
                   
                     
                       arg 
                       cw 
                     
                     ⁢ 
                     max 
                     ⁢ 
                     
                       
                         ∑ 
                         
                           i 
                           = 
                           1 
                         
                         p 
                       
                       ⁢ 
                       
                         
                           ( 
                           
                             
                               l 
                               in 
                             
                             , 
                             
                               l 
                               cw 
                             
                           
                           ) 
                         
                         2 
                       
                     
                   
                 
               
             
             
               
                 Eq 
                 . 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
   
   Wherein, l in  is an input LSP coefficient vector with a order of p, l cw  is a codeword vector of a codebook with a order of p and p is a order of a vector. cw is a codeword index. 
   The codebook searcher  530  searches the highband codebook  577  in the highband codebook  577  corresponding to the index  501  searched by the lowband codebook searcher  520  and outputs a codeword corresponding to the highband LSP. 
   The type converter B  540  converts the highband LSP coefficient into a highband LPC coefficient  502 . 
   The lowband codebook  567  and the highband codebook  577  are trained beforehand in offline. 
   The codebook training block  590  includes a wideband voice data base (DB)  550 , a low pass filter  560 , a down-sampler  561 , a lowband voice DB  562 , a lowband LPC analyzer  563  a lowband type converter  564 , a lowband LSP DB  565 , a lowband vector quantizer  566 , a high pass filter  570 , a highband voice DB  572 , a highband LPC analyzer  573 , a highband type converter  574 , a highband LSP DB  575  and a highband vector quantizer  576 . 
   The detail operation of the codebook training block  590  will be described hereinafter. 
   The wideband voice DB  550  stores 16 kHz wideband voice materials. 
   The low pass filter  560  removes a highband component for every 16 kHz wideband voice samples and generates lowband voice samples in 16 kHz, and then passes the samples to the down-sampler  561 . 
   The down-sampler  561  converts a sampling frequency of the lowband voice samples from 16 kHz into 8 kHz and generates 8 kHz lowband voice samples. These 8 kHz lowband voice samples are stored in the lowband voice DB  562 . 
   The lowband LPC analyzer  563  performs a LPC analysis for lowband voice frames and generates lowband LPC coefficients for the frame. 
   The lowband type converter  564  converts the lowband LPC coefficients vector analyzed by the lowband LPC analyzer  563  into a lowband LSP vector which is a parameter type proper to vector quantization. By repeating the process from the lowband LPC analyzer  563  to the lowband type converter  564  for every frame of all the 8 kHz lowband voice samples in the lowband voice DB  562 , the lowband LSP DB  565  is created. The lowband LSP DB  565  stores the LSP coefficients vectors for all of the 8 kHz lowband voice samples in the lowband voice DB  562  as training set. 
   The lowband vector quantization (VQ) trainer  566  separates the lowband LSP DB  565 , the training data into groups representing classes and then calculates the representatives of the classes. The lowband codebook is the set of the representatives. A Linde, Buzo, Gray (LBG) algorithm or Liyod algorithm is generally used as a training algorithm. Class information corresponding to each LSP coefficient vector obtained additionally by the lowband VO trainer  566  are passed to the highband VO trainer  576 . 
   In similar to the process for generating the lowband codebook  567 , the high pass filter  570  removes a lowband component from the 16 kHz wideband voice samples and generates 16 kHz highband voice samples. The 16 kHz highband voice samples are stores at the highband voice DB  572 . 
   The highband LPC analyzer  573  performs a LPC analysis for highband voice frames and generates highband LPC coefficients for the frame. 
   The highband type converter  574  converts the highband LPC coefficients vector analyzed by the highband LPC analyzer  573  into a highband LSP vector which is a parameter type proper to vector quantization. By repeating the process from the highband LPC analyzer  573  to the highband type converter  574  for every frame of all the 16 kHz highband voice samples in the lowband voice DB  562 , the highband LSP DB  575  is created. The highband LSP DB  575  stores the LSP coefficients vectors for all of the 16 kHz highband voice samples in the highband voice DB as training set. 
   Each highband LSP coefficients vector in the highband LSP DB  575  is one-to-one mapped to each lowband LSP coefficients vector in the lowband LSP DB  565 . 
   The highband VO trainer  576  generates the highband codebook  577  by calculating a mean value of the LSP coefficient vectors corresponding to each class based on the class information passed from the lowband VO trainer  566 . The lowband codebook  567  and the highband codebook  577  can be queried by the identical index. The process for generating the highband LPC coefficient is based on the mutual correlation of the lowband information and the highband information of the voice signals. 
   As above-mentioned, the method of the present invention can be embodied as a program and stored in recording media readable by a computer, e.g., CD-ROM, RAM, floppy disk, hard disk, magneto-optical disk, etc. 
   The present invention decrease the voice quality degradation due to the packet loss and the frame error in highband of the spilt-band voice codec so that provides high quality wideband voice telecommunication and can be applicable to any kind of highband voice coding scheme e.g., CELP, Transform coding, and waveform coding, etc. 
   The present application contains subject matter related to Korean patent application no. 2003-97824, filed in the Korean Intellectual Property Office on Dec. 26, 2003, the entire contents of which being incorporated herein by reference. 
   While the present invention has been described with respect to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.