Rule-based speech analysis and application of CELP coding

An approach is presented for efficiently encoding speech signals at low bit rates, by exploiting a combination of various speech analysis and compression techniques cooperating via a rule-based reasoning system. A front-end analyzer compresses speech events at nonuniformly spaced time intervals, by resorting to dynamic and static variable-frame-rate methods relevant to perception models. Then a codebook-excited-linear-predictive (CELP) coder performs a perceptually meaningful identification and quantization of the excitation parameters, to provide an optimal rendition of the original signal. This coding scheme can reduce the transmission rate down to 2.4-2.8 kb/s, while retaining a very good quality. The main applications are in voice response systems and voice mail.>