A multi-pulse LPC speech codec using digital signal processors

A full-duplex 16 or 9.6 k bits/sec speech codec based on the multi-pulse excited LPC coding technique has been developed. Cross-correlation analysis was used for the pulse search method. The codec was implemented by using five NEC 7720 Digital Signal Processor LSI chips ; four DSPs for the coder and one DSP for the decoder. A general purpose microprocessor was also used for system control. Reconstructed speech was quite natural and almost undiscernible from original speech at 16 k bits/sec and still quite good at 9.6 k bits/sec. Signal to noise power ratio for a sine wave signal was 30 dB at 16 k bits/sec.