A new speech processing scheme for ATM switching systems

From the viewpoint of speech communication services for the asynchronous transfer mode (ATM) network and in order to introduce the necessary conditions for speech processing over an ATM network, the authors have developed a novel speech-processing scheme applied at the end of the ATM network. For this speech processing, speech signals are processed basically by two techniques: silence deletion for speech compression and low-bit coding for 32-kb/s adaptive differential PCM (ADPCM). In order to reduce speech quality degradation caused by lost ATM cells in network congestion conditions, the authors propose a cell-reconstruction algorithm using waveform substitution for ADPCM-coded speech based on the pitch estimation method. In addition, to maintain good speech quality, some new algorithms for speech processing are introduced. It was confirmed through subjective evaluation tests that the proposed speech-processing scheme for the ATM network could provide good speech quality up to a cell loss rate of about 3%. Two kinds of custom LSIs for implementing these speech-processing algorithms are described