A new variable rate speech coder based on fuzzy phonetic classification and CS-ACELP structure

This paper presents a new variable bit-rate CELP speech coder based on fuzzy phonetic classification and CS-ACELP structure. The codec exploits new robust algorithms of multilevel phonetic classification and efficient activity/inactivity speech coding models. It uses 8 operating modes ranging from 0 to 8 kbit/s with an average bit rate of 4 kbit/s and an algorithmic delay of 15 ms. Subjective listening tests, performed in several acoustic noise conditions, demonstrate that performance is better than that of the GSM full-rate codec at 13 kbit/s and similar to that of the latest ITU-T standard for speech coding at 8 kbit/s, both in the discontinuous transmission mode.