Subjective effects of anomalies in packetized speech transmission

Abstract

When speech is transmitted in a packet-switched network the variability in packet delays inherent in such a net tends to produce occasional anomalies or “glitches” in the output speech when packets fail to arrive at the destination in a timely fashion. While the frequency of occurrence of these anomalies can be minimized at the expense of buffering and increased overall speech delay, it is likely that a practical network design would represent a compromise which allowed some degradation of the output speech under worst case load conditions. To provide some basic data on the subjective effects of such anomalies a series of listening and communicability tests has been undertaken using speech in which anomaly effects have been introduced by simulation techniques. Anomalies resulting from packet losses due to delay dispersion as well as variation in average delay are introduced at controlled rates in simulated networks using a variety of speech encoding techniques and packetization strategies. Preliminary test results will be presented and a tape with examples of some anomaly effects will be played. [This work was sponsored by the Defense Communications Agency for the Department of Defense.]