A Variable Low Bit Rate Speech Coder Based on Melp for Wireless Communications

Abstract

This paper proposes a novel variable low bit rate speech coding algorithm based on mixed excitation linear predictive (MELP) coder. This coder use a superframe structure and joint quantization methods to reduce the inter-frame redundancy of the parameters. In each superframe, the similarity of the linear prediction filter denoted by LSF parameters is imposed to reduce the bit rate by variable rate speech coding. A new distance measurement for LSF is proposed to describe the difference between two sets of LSF parameter. And the coding rate is decided by the distance measures of different LSF parameters in every superframe. Objective test results of synthesized speech quality show that the proposed speech coder is capable of maintaining acceptable speech quality at the rates 560 bps and 800 bps.