Identification of normal and abnormally rough vowels by spectral noise level measurements.

Our goal in this study was to learn whether vowel spectral noise level (SNL) measurements might differentiate between normal and abnormally rough test vowel samples. The vowel samples studied were obtained originally for two previous investigations. In one study, 20 normal-speaking subjects phonated in isolation each of five test vowels both normally and with simulated abnormal vocal roughness. In the other, 20 subjects who individually presented a laryngeal pathology phonated each of the same test vowels in isolation. The 300 test samples available from the two studies were obtained at one intensity and mouth-to-microphone distance (75 dB SPL at 15 cm). From the original studies, narrow-band (3-Hz) acoustic spectra of the vowel samples and SNL measurements were available. For this study, a mean of 25 noise level measurements per vowel sample served as an SNL index for each test production. Additionally, for this study, the test samples were individually classified dichotomously as normal or as abnormally rough in quality by a panel of nine listeners. Data analysis resulted in the identification of an SNL mean value (termed the SNL "criterion") that appeared to differentiate effectively between the perceptually normal and abnormally rough samples of each test vowel. In general, the findings appeared to support the hypothesis that vowel SNL measurements could be used to identify normal and abnormally rough vowel samples.