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