Detection of synchronization of the voice source and vocal tract in connected speech.

The purpose of this study was to investigate the degree to which the coupling between the oscillating sound source and the vocal tract filter occurs in connected speech samples, and to provide insight into how humans may choose to deploy this coupling for intelligibility, intensity, or both. A technique was developed to extract, from minutes-long speech samples, the time-dependent fundamental frequency (fo) and the first two formant frequencies (F1 and F2) to permit an analysis that determines whether a talker aligns a voice source harmonic with a vocal tract resonance, and also measures a normalized vowel space area. The accuracy of the processing method was validated by applying it to a set of audio samples generated via speech simulation that provided "ground-truth" data. It was then applied to a 41-talker database of clear and conversational speech. Results indicated that talkers make adjustments for different speaking styles that include not only increased vowel space area but also alignment of harmonics and formant frequencies, although future work is needed to determine whether these adjustments are directed toward maximizing transfer of information or transfer of acoustic power.