Vocal stability and vocal tract configuration: an acoustic and electroglottographic investigation.

Previous studies have reported differences in vocal fundamental frequency perturbation (jitter) and amplitude perturbation (shimmer) measures as a function of vowel type. However, it is not clear from those studies whether these effects derive from modifications in the shape of the vocal tract or from intrinsic vowel differences in mean fundamental frequency and vocal amplitude. The present study sought to address this issue using simultaneously obtained acoustic and electroglottographic (EGG) signals. Ten normal adult men and 10 normal adult women prolonged three maximally stable productions of the vowels [symbol: see text]. Vocal sound pressure level was maintained at 74 +/- 4 dB, while mean fundamental frequency was maintained at 110 and 220 Hz +/- 0.5 st for the male and female subjects, respectively. Results indicated that when vocal frequency and intensity are controlled, acoustic and EGG measures of mean jitter and shimmer do not show a significant vowel effect.