Effects of Speech Rate and Pitch Contour on the Perception of Synthetic Speech

Abstract

The increased use of voice-response systems has resulted in a greater need for systematic evaluation of the role of segmental and suprasegmental factors in determining the intelligibility of synthesized speech. Two experiments were conducted to examine the effects of pitch contour and speech rate on the perception of synthetic speech. In Experiment 1, subjects transcribed sentences that were either syntactically correct and meaningful or syntactically correct but semantically anomalous. In Experiment 2, subjects transcribed sentences that varied in length and syntactic structure. In both experiments a text-to-speech system generated synthetic speech at either 150 or 250 words/min. Half of the test sentences were generated with a flat pitch (monotone) and half were generated with normally inflected clausal intonation. The results indicate that the identification of words in fluent synthetic speech is influenced by speaking rate, meaning, length, and, to a lesser degree, pitch contour. The results suggest that in many applied situations the perception of the segmental information in the speech signal may be more critical to the intelligibility of synthesized speech than are suprasegmental factors.