Comparing the Contributions of Amplitude and Phase to Speech Intelligibility in a Vocoder-Based Speech Synthesis Model

Abstract

Vocoder-based speech synthesis model has been long used to assess the contribution of acoustic cue for speech recognition. This study compared the perceptual contributions of amplitude and phase by using two types of stimuli, i.e., amplitude-and phase-based vocoded stimuli. The amplitude-based vocoded stimuli were synthesized by preserving amplitude fluctuation cue but discarding phase cue (i.e., setting phase to zero), while the phase-based vocoded stimuli were synthesized by preserving phase cue and discarding amplitude cue (i.e., setting amplitude to unit). Listening experiments with normalhearing participants showed consistent findings with earlier studies that the intelligibility scores of both amplitude-and phase-based vocoded stimuli increased when using a large number of channels in vocoder-based speech synthesis. In addition, at all tested conditions, the intelligibility scores of amplitude-based vocoded stimuli were significantly larger than those of phase-based vocoded stimuli, suggesting that amplitude might carry more perceptual contribution than phase. This intelligibility advantage of amplitude over phase may be attributed to the difference in the amount of envelope information contained in the two types of vocoded stimuli.