Reconstruction Algorithm of Band Pass Voicing Coefficients Based on Mode Transition and Codebook Mapping

High efficient quantization of band pass voicing coefficients (BPVC) for the super frame plays an important role in low-bit-rate speech coding algorithms based on mixed excitation linear prediction (MELP). A reconstruction algorithm of BPVC based on mode transition and codebook mapping is proposed in this paper. It defines the transition mode according to the quantization index for BPVC of the current super frame as well as the last one. A codebook should be constructed for the decoder part, each vector of which corresponds to one transition mode. Decoder would find the corresponding reconstruction BPVC in the codebook according to the quantization index of the current super frame as well as the last one. Test results show that the algorithm could reduce the quantization error of BPVC by 20% above and improve the synthesis speech quality accordingly.