Development of high performance DCMS with 3-bit and 4-bit coding ADPCM

A digital circuit multiplication system (DCMS), which is equipped with an echo canceller to perform activity detection by applying reciprocal action between an echo canceller and a speech detector, is described. A high-quality speech detector, developed by introducing a hangover controller and linear predictive coding (LPC) analysis, and a trial model of the DCMS using advanced adaptive differential pulse-code modulation (ADPCM) which allowed 4-bit coding for voiceband data (VBD) signals, are presented. Efficiency improved by 10% using 4-bit coding for VBD.<>