Subjective effects of phase delay on synthesized speech

The contents of this paper describes the results of a study to determine the subjective effects of phase delay on synthesized speech. It is well known that synthesized speech is generally associated with a "machine-like" quality. Previously performed work in the speech processing field has shown that phase differentials over the speech spectrum in some cases improve the speech quality. However, no significant effort has been made to quantize these observations with respect to types and magnitude of phase shift versus listener acceptance. This paper summarizes a preliminary study which does relate these parameters. Independent agency scoring has provided a realistic correlation between phase shift and listener acceptability observations.