Algebraic code-excited linear prediction speech coding method

Claim 1

In a code-excited linear prediction (CELP) speech coding method, comprising the steps of: digitizing a speech signal as successive frames of L samples; adaptively determining synthesis parameters defining synthesis filters, and excitation parameters including, for each frame, pulse positions in an excitation code of L samples belonging to a predetermined algebraic codebook and an associated excitation gain; and transmitting quantization values representative of the determined parameters, wherein the algebraic codebook is defined on the basis of at least one group of N sets of possible pulse positions in codes of at least L samples, a code from the codebook being represented by N pulse positions belonging respectively to the N sets of positions of a group, wherein determining the excitation parameters relating to a frame includes selecting a code from the codebook which maximizes a quantity P k 2 /α k 2 , in which P k =D·c k T denotes the scalar product of a code c k from the codebook and a target vector D depending on the speech signal of the frame and on the synthesis parameters, and α k 2 denotes the energy in the frame of the code c k filtered by a compound filter made up of the synthesis filters and a perceptual weighting filter, calculating the energies α k 2 including calculating and storing in a memory components of a covariance matrix U=H T ·H, where H denotes a lower triangular Toeplitz matrix with L rows and L columns, formed from the impulse response h(0), h(1), . . . , h(L-1) of said compound filter; the improvement comprising, for at least one group of N sets, storing in the memory only those components of the covariance matrix which are of the form: ##EQU16## with 0≦p<N and those which are of the form: ##EQU17## pos i ,p and pos j ,q respectively denoting the positions of order i and j in the sets of said group containing possible positions for the pulses p and q of the codes from the codebook.