Variable-rate harmonic speech coder with efficient spectral quantization

This paper presents a high quality harmonic coder for variable-rate speech coding. An efficient variable-rate quantization technique is adopted for the quantization of the speech spectrum envelope. In this technique, the line spectrum pair (LSP) parameters of each speech frame are split and the prediction residuals of the LSP parameters are subsequently quantized by using the variable-dimension vector quantization (VQ) method. The splitting of LSP parameters is based on a voiced/unvoiced (V/UV) transition frequency. This V/UV transition frequency is determined from the closed-loop minimization of a V/UV matching error in the frequency domain. The proposed coder achieves good quality for speech communications at an average bit rate of about 1.9 kbps.