Algebraic code-excited linear prediction speech coding method
AssigneeFrance Telecom
InventorClaude Lamblin
Life of this patent
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Abstract
The method uses the technique of CELP coding with algebraic codebook. The search for the CELP excitation includes a calculation of certain components of the covariance matrix U=H.sup.T .multidot.H where H denotes a lower triangular Toeplitz matrix formed on the basis of the impulse response of a compound filter made up of synthesis filters and of a perceptual weighting filter. The memory-stored components of the covariance matrix are only those of the form U(pos.sub.i,p,pos.sub.i,p) and those of the form U(pos.sub.i,p, pos.sub.j,q), pos.sub.i,p and pos.sub.j,q respectively denoting position i and position j for the pulses p and q in the codes of the algebraic codebook.
Claims13
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.sub.k.sup.2 /.alpha..sub.k.sup.2, in which P.sub.k =D.multidot.c.sub.k.sup.T denotes the scalar product of a code c.sub.k from the codebook and a target vector D depending on the speech signal of the frame and on the synthesis parameters, and .alpha..sub.k.sup.2 denotes the energy in the frame of the code c.sub.k filtered by a compound filter made up of the synthesis filters and a perceptual weighting filter, calculating the energies .alpha..sub.k.sup.2 including calculating and storing in a memory components of a covariance matrix U=H.sup.T .multidot.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.ltoreq.p<N and those which are of the form:
- ##EQU17## pos.sub.i,p and pos.sub.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.
Dependencies are inferred from the claim text.