Spectral Properties and Quantitative Evaluation of Hypernasality in Vowels

Abstract

A new technique for evaluating hypernasality using an acoustic approach is presented. In a preliminary study using this technique, nasal resonance was assessed in 17 normal subjects and 16 subjects judged to be hypernasal. Analyses of the one-third-octave power spectra revealed an increase in power level between the first and second formant, and a reduction in the power level in second and third formant regions among utterances judged to be hypernasal. Factor analysis of the perceptual ratings revealed that the consensus perception of hypernasality accounted for 71% of the total variance. An additional 8% was accounted for by individual differences. Multiple regression analysis revealed a high correlation between the consensus perception of hypernasality and the variance in two acoustic-power levels, these being the power level between the first and second formant and the power level of the second and third formant regions.

Spectral characteristics of hypernasality in maxillectomy patients 1

“…Acoustic analysis has provided valuable information regarding hypernasality ( Forner, 1983; Philips & Kent, 1984) and synthesized nasal speech ( Kingston & Macmillan, 1995), but involved difficulties in quantifying spectral characteristics. One method to simply demonstrate the spectral characteristics of hypernasality is to measure the amplitude of the spectra at 1/3‐octave intervals ( Kataoka, 1988; Kataoka et al ., 1996 ). This specific bandwidth was selected because, over a broad frequency range, it compares well with the critical bandwidth of the analysing mechanism utilized by the ear ( Pols, van der Kamp & Plomp, 1969).…”

“…The spectral characteristics of hypernasality demonstrated in the current study were nearly identical to the results obtained from the study of cleft palate patients ( Kataoka et al ., 1996 ), in which almost the same spectral analysis was used. Consequently, the spectrum of hypernasality is considered to be consistent, even though the causes of nasal resonances are physiologically different.…”

“…The speech samples were acoustically analysed by a modification of the method previously used for assessment of hypernasality in cleft palate patients ( Kataoka et al ., 1996 ). Briefly, each speech sample was low‐pass filtered below 8 kHz with a roll‐off of 84 dB per octave, and digitized at a sampling rate of 20 kHz using a 16‐bit analog‐to‐digital converter (Sound Master 3) for storage on floppy disk.…”

“…Several acoustic measurements have been conducted to quantitatively evaluate hypernasality in cleft palate patients ( Forner, 1983; Philips & Kent, 1984; Kataoka, 1988; Kataoka et al , 1996 ). However, the cause of hypernasality in maxillectomy patients physiologically differs from that in cleft palate patients: hypernasality in the former results from ineffective oronasal separation, while in the latter it results from velopharyngeal inadequacy.…”

“…We previously reported the correlation of spectral properties and quantitative evaluation of hypernasality in acoustic analysis of cleft palate children ( Kataoka et al ., 1996 ). This study was carried out to reveal acoustic characteristics associated with hypernasality in maxillectomy patients and to establish their correlation to the severity of hypernasality, by modification of the approach used for cleft palate patients.…”