Method of and device for speech signal coding and decoding by vector quantization techniques

Claim 1

A method of coding and decoding speech signals, comprising the steps of: (I) coding speech signals by: (a) subdividing each speech signal into a block of samples x(j), (b) subjecting each block of samples x(j) to linear-prediction inverse filtering with quantized filter coefficient vectors a h (i) selected from a codebook of said quantized filter coefficient vectors and with a vector of index h ott forming an optimum filter which minimizes a spectral-distance function d LR from among normalized-gain linear-prediction filters, and obtaining a residual signal R(j) subdivided into residual vectors R(k), (c) comparing each of said residual vectors R(k) with each vector of a codebook of quantized residual vectors R n (k), thereby obtaining N difference vectors E n (k) where (1≦n≦N); (d) subjecting the N difference vectors E n (k) obtained in step (I) (c) to filtering with a frequency weighting function W(z) and extracting filtered quantization error vectors E n (k) therefrom; (e) automatically computing a mean-square error mse n for each of the filtered quantization error vectors extracted in step (I) (d), and (f) forming the coded speech signal from indices n min of the quantized residual vectors R n (k) which have generated a minimum value of the mean-square error mse n computed in step (I) (e) and from the index h ott for each block of samples x(j); and (II) decoding coded speech signals by: (a) selecting quantized residual vectors R n (k) having an index n min from said codebook of quantized residual vectors R n (k), (b) subjecting the selected quantized residual vectors of step (II) (a) to a linear-prediction filtering, and (c) supplying as coefficients for the linear-prediction filtering of step (II) (b), vectors a h (i) having the index h ott to thereby obtain quantized digital samples x(j) of a reconstructed speech signal.

Claim 2

A method of coding and decoding speech signals, comprising the steps of: (I) coding speech signals by: (a) subdividing each speech signal into a block of samples x(j), (b) subjecting each block of samples x(j) to linear-prediction inverse filtering with quantized filter coefficient vectors a h (i) selected from a codebook of said quantized filter coefficient vectors and with a vector of index h ott forming an optimum filter which minimizes a spectral-distance function d LR from among normalized-gain linear-prediction filters, and obtaining a residual signal R(j) subdivided into residual vectors R(k), (c) comparing each of said residual vectors R(k) with each vector of a codebook of quantized residual vectors R n (k), thereby obtaining N difference vectors E n (k) where (1≦n≦N); (d) subjecting the N difference vectors E n (k) obtained in step (I) (c) to filtering with a frequency weighting function W(z) and extracting filtered quantization error vectors E n (k) therefrom; (e) automatically computing a mean-square error mse n for each of the filtered quantization error vectors extracted in step (I) (d), and (f) forming the coded speech signal from indices n min of the quantized residual vectors R n (k) which have generated a minimum value of the mean-square error mse n computed in step (I) (e) and from the index h ott for each block of samples x(j); and (II) decoding coded speech signals by: (a) selecting quantized residual vectors R n (k) having an index n min from said codebook of quantized residual vectors R n (k), (b) subjecting the selected quantized residual vectors of step (II) (a) to a linear-prediction filtering, and (c) supplying as coefficients for the linear-prediction filtering of step (II) (b), vectors a h (i) having the index h ott to thereby obtain quantized digital samples x(j) of a reconstructed speech signal.

Claim 6

An apparatus for the coding and decoding of speech signals, comprising: for coding of speech signals: (a) a low-pass filter receiving at an input thereof, analog speech signals to be encoded, (b) an analog-to-digital converter connected to an output of said low-pass filter to output blocks of digital samples x(j) representing said analog speech signals, (c) a first register unit connected to an output of said analog-to-digital converter for temporarily storing said blocks of digital samples x(j), (d) a first computing circuit connected to said first register unit and receiving samples therefrom for computing autocorrelation coefficient vectors C x (i) of digital samples of each block received from said first register unit, (e) a first read-only memory containing H autocorrelation coefficient vectors C a (i,h) of quantized filter coefficients a h (i), where (1≦h≦H), (f) a first minimum-value calculator connected to said first computing circuit and to said first read-only memory for determining a spectral distance function d LR for each vector of coefficients C x (i) received from said first computing circuit and for each vector of coefficients C a (i,h) received from said first read-only memory, and determining a minimum of H values of d LR obtained for each vector of coefficients C x (i) and supplying to an output of the first minimum-value calculator a corresponding index h ott , (g) a second read-only memory connected to said output of the first minimum-value calculator and containing a codebook of the quantized filter coefficients a h (i) and addressed by the indices h ott from said first minimum-value calculator, (h) a digital inverse first linear-prediction filter connected to an output of said first register unit and to an output of said second read-only memory for receiving said blocks of samples from said first register unit and vectors of coefficients a h (i) from said second read-only memory, for generating a residual signal R(j), (j) a second register unit connected to said first linear-prediction filter for temporarily storing residual signals R(j) generated by said first linear-prediction filter and outputting residual vectors R(k), (k) a third read-only memory containing a codebook of quantized residual vectors R n (k), (l) a subtracting circuit connected to said second register unit and to said third read-only memory for computing for each residual vector R(k) outputted by said second register unit a difference with respect to each vector supplied by said third read-only memory, (m) a digital second linear-prediction filter connected to said subtracting circuit and receiving said differences therefrom for frequency weighting of vectors received from said subtracting circuit, thereby outputting a vector E n (k) of filtered quantization error, (n) a second computing circuit connected to said second linear-prediction filter for calculating a mean-square error mse n for each vector of filtered quantization error outputted by said second linear-prediction filter, (o) a second minimum-value calculator connected to said second computing circuit and identifying for each residual vector R(k), a minimum mean-square error obtained from the second computing circuit and delivering to an output of the second minimum-value calculator a corresponding index n min , and (p) a third register unit connected to said first minimum-value calculator through a delay circuit and connected to said second minimum-value calculator for outputting a coded signal for each block of samples in the form of the respective indices n min and h ott ; and for decoding of speech signals: (q) a fourth register unit for receiving a coded speech signal to be decoded and connected to said second and third read-only memories for temporarily storing the coded speech signal to be decoded and supplying the indices h ott thereof as addresses to said second read-only memory and the indices n min thereof as addresses to said third read-only memory, (r) a digital third linear-prediction filter connected to said second and third read-only memories for receiving respectively vectors of the coefficients a h (i) and quantized residual vectors R n (k) as addressed by said fourth register unit and outputting corresponding digital samples, and (s) a digital-to-analog converter connected to said third linear-prediction filter and receiving the digital samples outputted thereby, for supplying decoded analog speech signals.

Claim 7

An apparatus for the coding and decoding of speech signals, comprising: for coding of speech signals: (a) a low-pass filter receiving at an input thereof, analog speech signals to be encoded, (b) an analog-to-digital converter connected to an output of said low-pass filter to output blocks of digital samples x(j) representing said analog speech signals, (c) a first register unit connected to an output of said analog-to-digital converter for temporarily storing said blocks of digital samples x(j), (d) a first computing circuit connected to said first register unit and receiving samples therefrom for computing autocorrelation coefficient vectors C x (i) of digital samples of each block received from said first register unit, (e) a first read-only memory containing H autocorrelation coefficient vectors C a (i,h) of quantized filter coefficients a h (i), where (1≦h≦H), (f) a first minimum-value calculator connected to said first computing circuit and to said first read-only memory for determining a spectral distance function d LR for each vector of coefficients C x (i) received from said first computing circuit and for each vector of coefficients C a (i,h) received from said first read-only memory, and determining a minimum of H values of d LR obtained for each vector of coefficients C x (i) and supplying to an output of the first minimum-value calculator a corresponding index h ott , (g) a second read-only memory connected to said output of the first minimum-value calculator and containing a codebook of the quantized filter coefficients a h (i) and addressed by the indices h ott from said first minimum-value calculator, (h) a digital inverse first linear-prediction filter connected to an output of said first register unit and to an output of said second read-only memory for receiving said blocks of samples from said first register unit and vectors of coefficients a h (i) from said second read-only memory, for generating a residual signal R(j), (j) a second register unit connected to said first linear-prediction filter for temporarily storing residual signals R(j) generated by said first linear-prediction filter and outputting residual vectors R(k), (k) a third read-only memory containing a codebook of quantized residual vectors R n (k), (l) a subtracting circuit connected to said second register unit and to said third read-only memory for computing for each residual vector R(k) outputted by said second register unit a difference with respect to each vector supplied by said third read-only memory, (m) a digital second linear-prediction filter connected to said subtracting circuit and receiving said differences therefrom for frequency weighting of vectors received from said subtracting circuit, thereby outputting a vector E n (k) of filtered quantization error, (n) a second computing circuit connected to said second linear-prediction filter for calculating a mean-square error mse n for each vector of filtered quantization error outputted by said second linear-prediction filter, (o) a second minimum-value calculator connected to said second computing circuit and identifying for each residual vector R(k), a minimum mean-square error obtained from the second computing circuit and delivering to an output of the second minimum-value calculator a corresponding index n min , and (p) a third register unit connected to said first minimum-value calculator through a delay circuit and connected to said second minimum-value calculator for outputting a coded signal for each block of samples in the form of the respective indices n min and h ott ; and for decoding of speech signals: (q) a fourth register unit for receiving a coded speech signal to be decoded and connected to said second and third read-only memories for temporarily storing the coded speech signal to be decoded and supplying the indices h ott thereof as addresses to said second read-only memory and the indices n min thereof as addresses to said third read-only memory, (r) a digital third linear-prediction filter connected to said second and third read-only memories for receiving respectively vectors of the coefficients a h (i) and quantized residual vectors R n (k) as addressed by said fourth register unit and outputting corresponding digital samples, and (s) a digital-to-analog converter connected to said third linear-prediction filter and receiving the digital samples outputted thereby, for supplying decoded analog speech signals.