Variable rate speech coding with phonetic segmentation

A speech coder based on variable rate phonetic segmentation (VRPS), operating at an average rate of 3 kbit/s and applicable to code division multiple access (CDMA) digital cellular systems, is presented. An improved version of the voice activity detection scheme used in the GSM (Group Special Mobile) full-rate cellular standard tracks the bursty character of active speech. Each frame of active speech is classified into one of a set of four phonetic categories. A distinct coding configuration and bit-rate are applied to each category. The tradeoff between subjective quality and average bit rate of VRPS for both clean speech and speech corrupted with vehicle noise is superior to that obtained by QCELP, a proposed TIA speech coding standard for wideband digital cellular networks. The average bit-rate of VRPS is generally lower than that of QCELP for the same input signals.<>