Variable rate characteristic waveform interpolation speech coder based on phonetic classification

A variable-bit-rate characteristic waveform interpolation (VBR-CWI) speech codec with about 1.8 kbit/s average bit rate which integrates phonetic classification into characteristic waveform (CW) decomposition is proposed. Each input frame is classified into one of 4 phonetic classes. Non-speech frames are represented with Bark-band noise model. The extracted CWs become rapidly evolving waveforms (REWs) or slowly evolving waveforms (SEWs) in the cases of unvoiced or stationary voiced frames respectively, while mixed voiced frames use the same CW decomposition as that in the conventional CWI. Experimental results show that the proposed codec can eliminate most buzzy and noisy artifacts existing in the fixed-bit-rate characteristic waveform interpolation (FBR-CWI) speech codec, the average bit rate can be much lower, and its reconstructed speech quality is much better than FS 1016 CELP at 4.8 kbit/s and similar to G. 723.1 ACELP at 5.3 kbit/s.