4 kb/s improved multi-pulse based CELP speech coding with multiple location codebook and post-processing

This paper proposes an improved MP-CELP (Multi-Pulse-based CELP) speech coding at 4 kb/s. In MP-CELP, amplitudes or signs of multi-pulse excitation are simultaneonsly vector quantized (VQ). In order to improve speech quality for voiced speech, a multiple pulse location codebook is stored to enhance the coverage of the location. The optimum combination among the pulse location codebook, pulse amplitude codevector and gain codevector is searched for and selected. In order to be robust against background noise, a post-processing efficiently reduces temporal fluctuation for the excitation signal. The subjective evaluation results show that speech quality for 4 kb/s improved MP-CELP is equivalent to that for ITU-T G.726 (32 kb/s) and G.729 (8 kb/s) for both M-IRS and flat clean speech. For background noise conditions, 4 kb/s speech quality is close to that for ITU-T G.726 (32 kb/s).