Abstract
Summary The purpose of this investigation was to obtain information about the relationship between vocal sound pressure level (SPL) and the magnitude of cycle-to-cycle vocal fundamental frequency (jitter) and amplitude (shimmer) perturbation. Ten normal adult men prolonged the vowel/a/ in a modal register phonation in three SPL ranges: 60–68 dB (“soft”), 70–78 dB (“moderate”), and 80–88 dB (“loud”). A consistent trend related percent jitter and shimmer to the sound pressure level of the subjects' voices, such that the degree of perturbation was inversely related to the acoustic amplitude of the vowel. However, the relationship was more variable and less pronounced for shimmer measures, as only differences between the soft and loud SPL conditions were significant. These results nonetheless indicate that mean vocal intensity must be controlled or accounted for to maintain the validity and reliability of voice perturbation measurements. Possible physiologic explanations of the results and potential clinical implications are discussed.
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