Method and apparatus for speech coding
View Patent ↗A method and apparatus for prediction in a speech-coding system extends a 1 st order long-term predictor (LTP) filter, using a sub-sample resolution delay, to a multi-tap LTP filter. From another perspective, a conventional integer-sample resolution multi-tap LTP filter is extended to use sub-sample resolution delay. Such a multi-tap LTP filter offers a number of advantages over the prior-art. Particularly, defining the lag with sub-sample resolution makes it possible to explicitly model the delay values that have a fractional component, within the limits of resolution of the over-sampling factor used by the interpolation filter. The coefficients (β i 's) of the multi-tap LTP filter are thus largely freed from modeling the effect of delays that have a fractional component. Consequently their main function is to maximize the prediction gain of the LTP filter via modeling the degree of periodicity that is present and by imposing spectral shaping.
1. A method for coding speech by a speech coder, the method comprising the steps of:
receiving, by the speech encoder, an input signal;
generating, by the speech encoder, a target vector based on the input signal;
generating, by the speech encoder, a plurality of weighted adaptive codebook vectors based on a single sub-sample resolution delay value, an adaptive codebook, and a weighted synthesis filter;
generating, by the speech encoder, a weighted fixed codebook (FCB) excitation vector based on the target vector and the plurality of weighted adaptive codebook vectors;
generating, by the speech encoder, a plurality of correlation terms based on the target vector, the plurality of weighted adaptive codebook vectors, and the weighted FCB excitation vector; and
selecting, by the speech encoder, a gain vector from a table in response to an error minimization criterion, wherein the gain vector is comprised of at least two adaptive codebook gains and one fixed codebook gain, and where the error minimization criterion is based on the plurality of correlation terms.
2. The method in claim 1 , wherein the adaptive codebook gains form a symmetric long-term filter.
3. The method of claim 1 , wherein each generated weighted adaptive codebook vector of the plurality of generated weighted adaptive codebook vectors is associated with a different delay value and wherein a spacing between a delay value associated with a generated weighted adaptive codebook vector of the plurality of generated weighted adaptive codebook vectors and a delay value associated with another generated weighted adaptive codebook vector of the plurality of generated weighted adaptive codebook vectors has a non-integer sample resolution.
4. A method for coding speech by a speech coder, the method comprising generating, by the speech encoder, a plurality of adaptive codebook vectors based on a single sub-sample resolution delay value and an adaptive codebook, wherein each generated adaptive codebook vector of the plurality of adaptive codebook vectors is associated with a delay value and wherein the spacing between at least two adjacent delay values, each corresponding to its respective generated adaptive codebook vector, is different than one sample and is predetermined.
5. The method in claim 4 wherein the spacing between at least two adjacent delay values, each corresponding to its respective adaptive codebook vector, is one of a fraction of a sample and a value with an integer and fractional part.
6. The method of claim 4 , further comprising:
generating, by the speech encoder, a plurality of weighted adaptive codebook vectors ( c ′ 0 (n) . . . c ′ K-1 (n)) based on plurality of adaptive codebook vectors and on delay values that are defined with sub-sample resolution;
receiving, by the speech encoder, an input signal s(n);
generating, by the speech encoder, a target vector p(n) based on the input signal;
generating, by the speech encoder, a plurality of correlation terms (R cc (i,j),R pc (i)) based on the target vector p(n) and the plurality of weighted adaptive codebook vectors; and
generating, by the speech encoder, a plurality of multi-tap long-term predictor filter coefficients (β i 's) based on the plurality of correlation terms (R cc (i,j),R pc (i)).
7. A speech coder comprising a processor that is configured to receive an input signal, generate a target vector based on the input signal, generate a plurality of weighted adaptive codebook vectors based on a single sub-sample resolution delay value, an adaptive codebook, and a weighted synthesis filter, generate a weighted fixed codebook (FCB) excitation vector based on the target vector and the plurality of weighted adaptive codebook vectors, generate a plurality of correlation terms based on the target vector, the plurality of weighted adaptive codebook vectors, and the weighted FCB excitation vector; and select a gain vector from a table in response to an error minimization criterion, wherein the gain vector is comprised of at least two adaptive codebook gains and one fixed codebook gain, and where the error minimization criterion is based on the plurality of correlation terms.
8. A speech coder comprising a processor that is configured to generate a plurality of adaptive codebook vectors based on a single sub-sample resolution delay value and an adaptive codebook, wherein each generated adaptive codebook vector of the plurality of adaptive codebook vectors is associated with a delay value and wherein the spacing between at least two adjacent delay values, each corresponding to its respective generated adaptive codebook vector, is different than one sample and is predetermined.