Analysis-by-synthesis speech coding method with truncation of the impulse response of a perceptual weighting filter

An analysis-by-synthesis speech coding method for coding a speech signal digitized into successive frames which are subdivided into sub-frames, each sub-frame having a predetermined number of samples, the method comprising the steps of:

• performing a linear prediction analysis of the speech signal for each frame in order to determine coefficients of a short-term synthesis filter;
• performing an open-loop analysis for each frame in order to determine a degree of voicing of the frame;
• and
• performing at least one closed-loop analysis for each sub-frame in order to determine an excitation sequence which, submitted to the short-term synthesis filter, produces a synthetic signal representative of the speech signal, each closed-loop analysis using an impulse response of a composite filter consisting of the short-term synthesis filter and of a perceptual weighting filter, said impulse response being truncated to a truncation length which does not exceed said predetermined number of samples per sub-frame and which depends on an energy distribution of said response and on the degree of voicing of the frame.