Bit rate reduction of the MELP coder using Lempel-Ziv segment quantization

We previously proposed a new segment quantization method called Lempel-Ziv segment quantization (LZSQ), which is a modified version of Lempel-Ziv (LZ) coding that can be applied to a continuous information source. In the present paper, LZSQ is applied to the mixed excitation linear prediction (MELP) coder, which is a standardized vocoder-type speech coder that operates at 2.4 kbit/s, in order to reduce the bit rate to below 2.4 kbit/s, while preserving the quality of the coded speech. LZSQ is applied to six coding parameters of the MELP coder to reduce the total bit rate as much as possible. As a result, the total bit rate of the modified MELP coder was reduced to 1.57 kbit/s, while the subjective quality of the modified MELP coder is equivalent to that of the previous MELP coder.