Formant representation of parameters for a channel vocoder

Formant tracking and synthesis from formant information has been applied to a channel vocoder. The speech spectrum is first estimated with a 29 channel vocoder analyzer. Four crude formant values are obtained by processing the analyzer outputs. In the serial formant approach bandwidths and center frequencies for each formant are then computed by parabolic interpolation of neighboring channels. After normalization, bandwidths are recomputed so as to give a better match between measured and derived formant amplitudes. Finally, a spectrum derived from four formant frequencies, four formant bandwidths plus a single gain factor replaces the measured spectrum and the speech is synthesized by the spectrally flattened channel vocoder synthesizer. In the parallel formant approach, four formant frequencies, four formant amplitudes plus the amplitudes of the first and last channel are transmitted. The remaining channel signals are computed at the receiver by parabolic interpolation. Preliminary listening results indicate that these representations can be effective in reducing the bandwidth of a channel vocoder.