Adapting noise masking level in analysis-by-synthesis employing perceptual weighting

Analysis-by-synthesis speech coding method, comprising the following steps:

• linear prediction analysis of order p of a speech signal digitized as successive frames in order to determine parameters defining a short-term synthesis filter ;
• determination of excitation parameters defining an excitation signal to be applied to the short-term synthesis filter in order to produce a synthetic signal representative of the speech signal, some at least of the excitation parameters being determined by minimizing the energy of an error signal resulting from a filtering of a difference between the speech signal and the synthetic signal by at least one perceptual weighting filter having a transfer function of the form W(z)=A(z/.sub..gamma..sub.1)/A(z/.gamma..sub.2) where ##EQU12## the coefficients a.sub.i being linear prediction coefficients obtained in the linear prediction analysis step, and .gamma..sub.1 and .gamma..sub.2 denoting spectral expansion coefficients such that 0.ltoreq..gamma..sub.2 .ltoreq..gamma..sub.1 .ltoreq.1;
• and
• production of quantization values of the parameters defining the short-term synthesis filter and of the excitation parameters,
• wherein the value of at least one of the spectral expansion coefficients is adapted on the basis of spectral parameters obtained in the linear prediction analysis step.