Spectral characteristics of hypernasality in maxillectomy patients.

To reveal the acoustic characteristics associated with hypernasality and to ascertain their correlation to the severity of hypernasality, 30 speech samples produced by 15 maxillectomy patients were acoustically analysed with and without an obturator prosthesis in place. The isolated, sustained Japanese vowel /i/ was used as the stimulus for acoustic measurement and perceptual judgment to evaluate the severity of hypernasality. Normalized 1/3-octave spectral analysis demonstrated the spectral characteristics of hypernasality as a rise in amplitude between the first and second formants around the 1 kHz region, and a reduction in amplitude of the frequencies higher than the second formant. High correlation was shown between the perceptual ratings and the predicted values derived from stepwise regression analysis.