Method for searching an excitation codebook in a code excited linear prediction (CELP) coder
First Claim
1. In a linear prediction coder to provide synthesized speech in which short term and long term redundancies by a filter means having L taps wherein said filter means has an impulse response, h(n), are removed from a frame of N digitized speech samples resulting in a residual waveform of N samples, a method for encoding said residual waveform using k codebook vector, ck, comprising:
- convolving a target signal, x(n), and said impulse response, h(n) to provide a first convolution;
autocorrelating an impulse response matrix wherein said impulse response matrix is a lower triangular toeplitz matrix with diagonal h(0) where h(0) is the zeroth impulse response value and the lower diagonals h(1), . . . ,h(L-1) and wherein said impulse response autcorrelation is computed in accordance with the equation;
##EQU14## autocorrelating said synthesized speech in accordance with said autocorrelation of said impulse response matrix and said codebook vectors, ck to provide a synthesized speech autocorrelation, Eyy ;
cross correlating said synthesized speech and said target speech in accordance with said first convolution and said codebook vectors to provide a cross correlation Exy ; and
selecting a codebook vector in accordance with said cross correlation, Exy, and said synthesized speech autocorrelation, Eyy.
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Abstract
A method for selecting a code vector in an algebraic codebook wherein the analysis window for the coder is extended beyond the length of the target speech frame. By extending the analysis window, the two dimensional impulse response matrix can be stored as a one dimensional autocorrelation matrix greatly saving on the computational complexity and memory required for the search.
91 Citations
9 Claims
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1. In a linear prediction coder to provide synthesized speech in which short term and long term redundancies by a filter means having L taps wherein said filter means has an impulse response, h(n), are removed from a frame of N digitized speech samples resulting in a residual waveform of N samples, a method for encoding said residual waveform using k codebook vector, ck, comprising:
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convolving a target signal, x(n), and said impulse response, h(n) to provide a first convolution; autocorrelating an impulse response matrix wherein said impulse response matrix is a lower triangular toeplitz matrix with diagonal h(0) where h(0) is the zeroth impulse response value and the lower diagonals h(1), . . . ,h(L-1) and wherein said impulse response autcorrelation is computed in accordance with the equation;
##EQU14## autocorrelating said synthesized speech in accordance with said autocorrelation of said impulse response matrix and said codebook vectors, ck to provide a synthesized speech autocorrelation, Eyy ;cross correlating said synthesized speech and said target speech in accordance with said first convolution and said codebook vectors to provide a cross correlation Exy ; and selecting a codebook vector in accordance with said cross correlation, Exy, and said synthesized speech autocorrelation, Eyy. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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Specification