The Combined effect of speech codec quality and transmission delay on human performance during complex spoken interactions

This paper examines the effect of interaction between speech codec output quality and simulated satellite or VoIP transmission delay time on talker performance in a complex interaction. A hardware test codec (both single and tandem) was compared against a number of processed speech reference conditions to determine the relative subjective quality of the test codecs against conditions with known Mean Opinion Scores (MOS). The two codec conditions plus an additional higher quality condition were then used in an experiment that examined the effect of the interaction of transmitted speech quality and simulated transmission delay on a speech shadowing task and an accompanying error repair task involving two speakers. One person (the “reader”) read a passage. The second person (the “shadower”) shadowed the read passage by repeating immediately the words spoken by the reader. The reader, whilst reading, also listened for errors spoken by the shadower and repaired those errors by verbally reporting them to the shadower. A significant interaction between codec quality and transmission delay was found for the error repair task, but only for cases where the shadower made a significant number of errors. These results suggest that, for highly complex interactions which involve significant cognitive load, human performance will degrade more rapidly with increases in delay for transmission systems using speech codecs with lower quality output. This is assumed to be due to the additional demands upon working memory imposed by the transmission delay.22 page(s