Modulation frequency and modulation level owing to vocal microtremor.

Vocal microtremor designates a normal slow modulation of the vocal cycle lengths of speakers who do not suffer from pathological tremor of the limbs and whose voices are not perceived as tremulous. Vocal microtremor is therefore distinct from pathological vocal tremor. The objective is to report data about the modulation frequency and modulation level owing to vocal microtremor. The modulation data have been obtained for vowels [a], [i], and [u] sustained by normophonic and mildly dysphonic male and female speakers. The results are the following. First, modulation frequencies and relative modulation levels do not differ significantly for male and female speakers, normophonic and mildly dysphonic speakers, as well as for vowel timbres [a], [i], and [u]. Second, the typical interquartile intervals of the modulation frequency and modulation level are equal to 2.0-4.7 Hz and 0.4%-1.3%, respectively. Third, dissimilarities between data reported by different studies are due to different cutoff frequencies below which spectral peaks are considered not to contribute to vocal microtremor.