Missing speech packet reconstruction based on the short-time energy and the zero-crossings

A waveform substitution technique using interpolation based on such slow varying parameters of speech as short-time energy and average zero-crossing rate is developed for a packetized speech communication system. The system uses 64 Kbps conventional PCM for encoding and takes advantage of active talkpurts and silence intervals to increase the utilization efficiency of a digital link. The short-time energy and average zero-crossing rates calculated for the purpose of determining talkpurts are transmitted in a preceeding packet. Hence, when a packet is pronounced "lost", its envelope and frequency characteristics are obtained from the previous packet and used to synthetize a substitution waveform which is free of annoying sounds that are due to abrupt changes in amplitude. Informal listening tests show that tolerable packet loss rate up to 40% are achievable with these procedures.