The effect of waveform substitution on the quality of PCM packet communications

Missing packets are a major cause of impairment in packet voice networks. While it is easiest to allow these gaps in received speech to appear as silent intervals in reconstructed speech, speech quality is improved by filling the gaps with estimates of the transmitted waveform. Several estimation techniques have been investigated for packets containing 16 ms of speech in a pulse-code-modulation format. The simplest method, packet repetition, extends from 2% to 5%, the acceptable ratio of missing packets. Here, acceptability is defined as a mean opinion score midway between fair and good on a five-point opinion scale. The most effective estimation technique (although not the most complex) is pitch waveform replication. It extends the acceptable ratio of missing packets to 10%