High quality multi-pulse based CELP speech coding at 6.4 kb/s and its subjective evaluation

This paper proposes an MP-CELP (multi-pulse-based CELP) speech coding at 6.4 kb/s with a 10 ms frame. In MP-CELP, the amplitudes or signs of the multi-pulse excitation are simultaneously vector quantized (VQ). A combination search between the multiple pulse location candidates and the VQ codebook remarkably improves the quantization performance. In order to improve the speech quality for background noise conditions, an adaptive pulse location restriction method is developed. The subjective evaluation results show that the speech quality for 6.4 kb/s MP-CELP is higher than that for G.726 at 32 kb/s and is equivalent to that for 6.3 kb/s G.723.1 with a 30 ms frame in clean speech and tandem conditions. For background noise conditions, the adaptive pulse location restriction significantly improves the MOS value by 0.9. The speech quality is equivalent to that for G.723.1, but still does not reach that of 24 kb/s G.726, except under the interference talker condition