High quality MP-CELP speech coding at 12 kb/s and 6.4 kb/s

This paper proposes an MP-CELP (multi-phase-based CELP) speech coding, at bit rates of 12 kb/s and 6.4 kb/s, which is the higher and lower bit rates extension to ITU-T G.729. In MP-CELP, the amplitudes or signs of the multi-pulse excitation are simultaneously vector quantized (VQ). A combination search between pulse locations and the VQ codebook enhances the quantization performance. By restricting the pulse locations based on the algebraic structure, the location search complexity and the transmission bits are reduced. Further, in order to improve the LSP VQ performance at 6.4 kb/s, a combination search between multiple candidates of th LSP VQ codevectors and closed-loop lag candidates is developed. The speech quality for 12 kb/s and 6.4 kb/s MP-CELP is higher than that for G.726 at 32 kb/s and G.726 at 24 kb/s, respectively, in clean speech conditions.