Recovery of Missing Speech Packets Using the Short-Time Energy and Zero-Crossing Measurements

A waveform substitution technique using interpolation based on the slow varying speech parameters short-time energy and zero-crossing information is developed for a packetized speech communication system. The system uses 64 kbs conventional pulse code modulation (PCM) for encoding and takes advantage of active talkspurts and silence intervals to increase the utilization efficiency of a digital link. The short-time energy and information on the zero-crossings needed for the purpose of determining talkspurts are transmitted in a preceding packet. Hence, when a packet is pronounced "lost," its envelope and frequency characteristics are obtained from a previous packet and used to synthesize a substitution waveform which is free of annoying sounds that are due to abrupt changes in amplitude.