A 600 bps LPC voice coder

The authors describe a 600 bit/s vocoder that is based on the LPC-10 (linear prediction coding) vocoder model. The coder operates on the principle of selecting a point on the 600 bit/s rate distortion bound that is optimal given the rate of spectral change within a four-frame superframe of speech. The authors describe the tradeoffs in spectral coding, pitch coding, voice encoding, RMS encoding, synchronization, and forward error correction. The perceptual weighting criteria used are shown to select reasonable operating points on the rate distortion bound as speech spectra change from quasi-stationary to rapidly dynamic