VARIABLE RATE SPEECH CODING METHOD AND DECODING METHOD

摘要

In a variable rate speech coding method for a CELP speech coding system, an adaptive sound source vector and a first noise source vector are selected from a sound source code book and a noise source code book so that a first synthesized speech signal is obtained which has a minimum distortion relative to an input speech signal. A virtual reference speech signal is generated using a sound source signal which is produced using the adaptive sound source vector. A second noise source vector corresponding to the adaptive sound source vector is selected so that a second synthesized speech signal is obtained which has a minimum distortion relative to the virtual reference speech signal. The sending of a noise source code book index corresponding to the first noise source vector is suspended according to the quality of the second synthesized speech signal.