A system for very low data rate speech communication

The system to be described processes the output of a 10th order LPC analyzer to obtain information characteristic of the four most prominent resonances in the LPC10 model spectra for voiced frames. Nonvoiced frames are specified by an LPC4 model. System operation for voiced frames depends upon the development of a set of reference clusters in the 4-dimensional spaces of resonance frequencies and spectral magnitudes; synthesis is performed with parallel resonators using the spectral representations for these clusters, with resonance bandwidths inserted according to rule. For nonvoiced frames clustering is done on log-area-ratios, with speech synthesized by a PARCOR filter. An extensive analysis of speech data was performed to obtain parameter quantization tables necessary for operation at rates from 1600 to 711 bits/sec. All critical computational processes have been demonstrated to operate in 16-bit arithmetic, and can be performed in real time on contemporary signal processing hardware.