A novel variable-rate MELP speech coder

In MELP coder, LPC coefficients are quantized to 25 bit/frame by MSVQ. The overall bit of MELP is 54 bit/frame, so more than 45% of the required bandwidth is spent on transmission of LPC coefficients. In this paper, based on LPC adaptive forward-backward quantization, a novel variable-rate MELP coder is proposed, in which linear prediction is done by using either the currently (forward LPC) or previously decoded (backward LPC) speech frame. The backward LPC scheme shall be applied, i.e., the LPC coefficients based on the previously decoded optimal speech frame are used to encode the current frame and only the time delay shall be transmitted to the decoder, so, average LPC bit number becomes smaller. Computer simulation shows significant average overall bit rate reduction is achieved without compromising the decoded speech quality