US 5,444,816 A · Dynamic codebook for efficient speech coding based on algebraic codes

Abstract

A method of encoding a speech signal is presented. This method improves the excitation codebook and search procedure of the conventional Code Excited Linear Prediction (CELP) speech encoders. Use is made of a dynamic codebook (201, 202) based on the combination of two modules: a sparse algebraic code generator (201) associated to a filter (202) having a transfer function varying in time. The generator (102) is a structured codebook with codewords having very few non zero components. The filter (202) shapes the spectral characteristics whereby the resulting excitation codebook (201, 202) exhibits favorable perceptual properties. The search complexity in finding the best codeword is greatly reduced by bringing the search back to the algebraic code domain thereby allowing the sparsity of the algebraic code to speed up the necessary computations.

Claims18

Dependent claims

A method of producing an excitation signal to be used by a sound signal synthesis means to synthesize a sound signal, comprising the steps of:

generating a codeword signal in response to an index signal associated to said codeword signal, said signal generating step using an algebraic code to generate said codeword signal;
and
prefiltering the generated codeword signal to produce said excitation signal, said prefiltering step comprising processing the codeword signal through an adaptive prefilter having a transfer function varying in time in relation to parameters representative of spectral characteristics of said sound signal to thereby shape frequency characteristics of the excitation signal so as to damp frequencies perceptually annoying a human ear.

A dynamic codebook for producing an excitation signal to be used by a sound signal synthesis means to synthesize a sound signal, comprising:

means for generating a codeword signal in response to an index signal associated to said codeword signal, said means for generating a codeword signal using an algebraic code to generate said codeword signal;
and
means for prefiltering the generated codeword signal to produce said excitation signal, said prefiltering means comprising an adaptive prefilter having a transfer function varying in time in relation to parameters representative of spectral characteristics of said sound signal to thereby shape frequency characteristics of the excitation signal so as to damp frequencies perceptually annoying a human ear.

Dependencies are inferred from the claim text.

Dynamic codebook for efficient speech coding based on algebraic codes

Life of this patent

Dynamic codebook for efficient speech coding based on algebraic codes

Life of this patent

Abstract

Claims18