An efficient codebook search algorithm for EVRC

In this paper, a fast implementation algorithm for EVRC encoder is presented. Among the routines of CELP-type speech coders, the fixed codebook search is the most computationally demanding. The fast algorithm developed in this study mainly concerns the fixed codebook search procedure. For efficient codebook search, two efficient schemes are developed: limiting the number of possible combination of pulse positions, and using a reduced-tap FIR filter instead of the impulse response of the weighted synthesis filter. The proposed EVRC algorithm was implemented using a fixed-point DSP, and the new EVRC algorithm was subjectively evaluated. It was found that the new FCB search routine could be implemented with only 24.3 % of the original one. Informal subjective tests confirmed that the speech quality of the proposed algorithm was indistinguishable from the original EVRC.