Pitch effects on vowel roughness and spectral noise for subjects in four musical voice classifications.

This study was designed to investigate the effects of vocal fo on vowel spectral noise level (SNL) and perceived vowel roughness for subjects in high- and low-pitch voice categories. The subjects were 40 adult singers (10 each sopranos, altos, tenors, and basses). Each produced the vowel /a/ in isolation at a comfortable speaking pitch, and at each of seven assigned pitches spaced at whole-tone intervals over a musical octave within his or her singing pitch range. The eight /a/ productions were repeated by each subject on a second test day. The SNL differences between repeated test samples (different days) were not statistically significant for any subject group. For the vowel samples produced at a comfortable pitch, a relatively large SNL was associated with samples phonated by the subjects of each sex who manifested the relatively low singing pitch range. Regarding the vowel samples produced at the assigned-pitch levels, it was found that both vowel SNL and perceived vowel roughness decreased as test-pitch level was raised over a range of one octave. The relationship between vocal pitch and either vowel roughness or SNL approached linearity for each of the four subject groups.

Relationship of spectral noise levels to psychophysical scaling of vowel roughness.

Direct magnitude estimation (DME) and equal-appearing interval (EAI) ratings of perceived roughness and spectral noise level (SNL) measurements of isolated sustained vowel samples (/a/ and /i/) were obtained. The linear and curvilinear relationships between the resulting roughness ratings and SNL were then examined. In the present study, the comparison between the two models resulted in conflicting evidence regarding the model that best described the relationship between roughness ratings and SNL measurements. In all comparisons, however, a significant linear component was indicated. Additionally, when a significant curvilinear component was indicated, the difference between the lines and curves that were fit to the data was minimal. The present findings suggest, therefore, that a high degree of linearity exists between both DME and EAI roughness ratings and SNL.

Direct magnitude estimation and equal appearing interval scaling of vowel roughness.

Direct magnitude estimation (DME) and equal-appearing interval (EAI) ratings of the perceived roughness of isolated sustained vowel samples (/a/ and /i/) were obtained. The linear and curvilinear relationship between the resulting EAI and DME ratings was then examined. That relationship was found to be more strongly curvilinear than linear, a characteristic of a prothetic continuum. The amount of variance accounted for by a curvilinear model of the relationship, however, was minimally more than that accounted for by a linear model. The findings thus suggest that the roughness continuum manifests no more than "a little" protheticness, if any. It does not seem clear from this initial study that there is greater validity associated with roughness ratings obtained by the DME than the EAI method. Rather, the findings suggest that a small degree of such advantage may exist, but it may be too small to be of practical consequence in many instances.

Spectral noise level measurements used to track voice improvement in one patient.

In this report we present one example of the utilization of an acoustic measurement to aid in describing voice roughness objectively in a clinical context. Vowel spectral noise level (SNL) and fundamental voice frequency (F0) measurements were acquired for five sustained vowels produced by one patient having bilateral vocal fold nodules. The measurements were obtained at specific time intervals while the patient underwent voice therapy. Clinically observed changes over the course of therapy included an improvement in perceived voice quality, a general reduction in vowel SNL, and an increase in vowel F0. These observations were accompanied by visually detected laryngeal tissue changes. The results suggest that acoustic SNL measurements can be employed clinically to verify and support perceptual judgments of voice quality.

Formant-frequency differences between isolated whispered and phonated vowel samples produced by adult female subjects.

This study was designed to investigate the formant frequencies of phonated and whispered productions of five test vowels (/i/, /u/, /ae/, /a/). Each test vowel was sustained twice in isolation--once phonated, one whispered--by 20 adult female subjects. The phoneme represented by each recorded production was identified independently by 11 listeners. Only those samples identified by 6 or more of the listeners as the vowel intended were retained for a further (acoustic) analysis. An acoustic spectrum of each retained sample was obtained to permit formant measurements. To provide the clearest formant delineation possible in our lab, the phonated samples were analyzed by broadband spectrography and the whispered samples by very narrow-band spectrography. This report presents the formant frequencies (F1-F3) of the test productions as measured from the acoustic vowel spectra and the formant-frequency differences between the phonated and whispered productions. In general, the results showed a trend for whispered vowel formants to be higher in frequency than phonated vowel formants, but that trend was only strongly evident for F1.

Airflow characteristics of stop-plosive consonant productions of normal-speaking children.

This study of children's speech was designed to investigate peak oral-nasal airflow during the production of stop-plosive consonants in isolated syllable contexts. The subjects were 30 normal-speaking children: five girls and five boys at each of three age levels (8, 9, and 10 years). Each subject produced each of six stop-plosive consonants (/p/, /b/, /t/, /d/, /k/, and /g/) in each of three syllable contexts (CV, VCV, and VC) with each of two vowels (/i/ and /a/). A pneumotachometer and an oscillographic recorder were used to obtain permanent airflow records of the test syllables. It was found that the peak flows varied according to the age of subjects, consonant voicing, place of consonant production, consonant position within the test syllable, and the vowel in combination with the test consonant. Results were compared to related findings previously obtained for children and adults.

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.

Harmonic levels and vowel roughness.

In this study the effects of vowel roughness on the level of harmonics in test vowel spectra were investigated. Twenty normal-speaking adult males sustained productions of each of the vowels (formula: see text) first normally and then with simulated abnormal vocal roughness, at one intensity. A tape recording of each production was rated for roughness on an equal-appearing intervals scale by 11 judges and was also analyzed to obtain its 3-Hz bandwidth amplitude-by-frequency acoustic spectrum. The median roughness rating, the level of the first five spectral harmonics, and the f0 of each production were obtained. It was found that the level of the first three harmonics for each test vowel diminished with an increase in roughness (as was hypothesized from earlier results), but the higher harmonics of /u/ and /i/ showed some reversals. A moderately large negative correlative relationship was shown between lower-harmonic levels and median vowel roughness. A possible explanation of the higher-harmonic reversals was offered. The results suggest that spectral noise level measurements may provide a more reliable acoustic index of vowel wave aperiodicity and vowel roughness than measurements of harmonic level.

Spectral noise levels and roughness severity ratings for vowels produced by male children.

This study investigated the relationship between spectral noise level (SNL) and perceived roughness in sustained vowels phonated by children. Twenty male children, ten presenting normal vocal quality and ten presenting vocal roughness associated with benign vocal cord lesions, served as subjects. The children individually sustained each of the vowels (Formula: see text) at one intensity and at two pitch levels (comfortable and high). Each vowel recording was analyzed to produce a 3-Hz bandwidth, amplitude-by-frequency acoustic spectrum. The levels of inharmonic (noise) components were measured for the range 100 to 2600 Hz within each vowel spectrum and the mean of those measures provided an index of vowel spectral noise level. Each recorded sample was also rated for degree of roughness, by 11 trained judges, using a five-point, equal-appearing intervals scale. The fundamental vocal frequency (fo) of each production also was measured. The results indicated that four subjects with vocal pathology phonated their vowel productions with a relatively extreme fo when compared to subjects with normal voice quality. It was also found that vowel roughness and SNL differed predictably for individual vowels and that, especially for normal-speaking subjects, roughness and SNL decreased with an increase in fo. Further, for both subject groups, SNL measures were correlated positively and moderately highly with perceived roughness.

Spectral noise and vocal roughness relationships in adults with laryngeal pathology.

Twenty adult males, presenting laryngeal pathology, each produced five vowels and two sentences for tape recording. Individual recordings were then rated for roughness on a 5-point equal-appearing intervals scale. Each vowel production was also analyzed spectrographically. High, positive correlations (multiple r) were obtained between vowel spectral noise measures (dB SPL) and median roughness ratings for the vowels and sentences. The findings, similar to those previously reported for subjects without pathology, suggest that the relationships shown are independent of laryngeal health. Vowel spectral noise measures appear to provide a useful quantitative index of vocal roughness in vowels and connected speech.

Some waveform and spectral features of vowel roughness.

Acoustic wave-period variation (jitter) and acoustic wave-amplitude variation (shimmer) associated with vowel phonations representing a range of vocal roughness were investigated. Twenty normal-speaking adult males phonated each of the vowels /u/, /i/, /v/, /a/, and /ae/, first normally and then with simulated abnormal vocal roughness. Twenty hoarse adult males, each presenting a medically diagnosed laryngeal pathology, also produced each of the five test vowels. To provide a measurable presentation of the frequency and amplitude variations of interest, each recorded vowel was band-pass filtered to isolate the fundamental frequency component. Relations of the jitter and shimmer indices (obtained from the filtered vowel waves) to acoustic spectral noise levels and to roughness ratings for the vowel phonations were studied. The findings supported the hypothesis that increases in vowel acoustic wave variability (estimated by period or amplitude variation or both) are associated with increases in vowel spectral noise levels and perceived vowel roughness. The findings also suggested, for most of the vowels studied, that cyclic peak amplitude variation may provide a better index of perceived roughness than cyclic period variation. Vowel spectral noise levels, however, may provide a more clinically useful indicant of vowel roughness than the waveform variability indices derived from the filtering procedure employed in this study.