CELP CODING AT VARIABLE-RATE

This paper describes the general principle of variable rate applied to CELP coding and presents an algorithm conceived for mobile applicatio ns based on CDMA technique. The speech coder operates at an average ra te of around 6 kbit/s with a peak rate of 16 kbit/s, providing a quali ty close to the one of the G.728 standard. The algorithm is based on a multi-rate CELP whose operating mode is selected by a combination of open-loop speech classification and closed-loop quality evaluation. Th e scheme is not fully optimized for the average rate, but attention ha s mainly been paid to the classification algorithm having the constrai nt to keep the algorithmic delay equal to 10 ms.