ACOUSTIC CUES OF VOWEL NASALIZATION: A SIMULATION STUDY.

Abstract

Acoustic correlates for vowel nasalization were investigated by means of speech synthesis using a realistic acoustic vocal-tract model including the nasal cavity system. This approach is characterized by high quality output speech signals, and the acoustic characteristics of the nasalized vowels can be calculated for any magnitude of the nasal cavity coupling. The relationships between the acoustic effect and the perceptual effect can be studied as a function of the coupling magnitude. It was found for the French vowels /i, a, and u/ that the acoustic and perceptual effects of the nasal coupling were vowel dependent. A global flattening of the spectra in the first and second formant region (from about 200 Hz to 2000 Hz) appeared to be a vowel independent cue of the nasalization. A proposed measure of spectral flatness explains the vowel dependent variation of the subjective degree of nasalization.