Molly L. Erickson

The Effect of an Artificially Lengthened Vocal Tract on Estimated Glottal Contact Quotient in Untrained Male Voices

The use of hard-walled narrow tubes, often called resonance tubes, for the purpose of voice therapy and voice training has a historical precedent and some theoretical support, but the mechanism of any potential benefit from the application of this technique is not well understood. Fifteen vocally untrained male participants produced a series of spoken /a/ vowels at a modal pitch and constant loudness, before and after a minute of repeated phonation into a 50-cm hard-walled glass tube at the same pitch and loudness targets. Electroglottography was used to measure the glottal contact quotient (CQ) during each phase of the experiment. Single-subject analysis revealed statistically significant changes in CQ during tube phonation, but with no discernable pattern across the 15 participants. These results indicate that the use of resonance tubes can have a distinct effect on glottal closure, but the mechanism behind this change remains unclear. The implication is that vocal loading techniques such as this need to be studied further with specific attention paid to the underlying mechanism of any measured changes in glottal behavior, and especially to the role of instruction and feedback in the therapeutic and pedagogical application of these techniques.

Dissimilarity and the classification of female singing voices: a preliminary study.

Traditionally, timbre has been defined as that perceptual attribute that differentiates two sounds when pitch and loudness are equal and thus is a measure of dissimilarity. By such a definition, each voice possesses a set of timbres, and the identity of any voice or voice category across different pitch-loudness-vowel combinations must be due to an abstraction of the pattern of timbre transformation. Using stimuli produced across the singing range by singers from different voice categories, this study sought to examine how timbre and pitch interact in the perception of dissimilarity. This study also investigated whether listener experience affects the perception of timbre as a function of pitch. The resulting multidimensional scaling (MDS) representations showed that for all stimuli and listeners, dimension 1 correlated with pitch, whereas dimension 2 correlated with spectral centroid and separated vocal stimuli into the categories mezzo-soprano and soprano. Dimension 3 appeared highly idiosyncratic depending on the nature of the stimuli and on the experience of the listener. Inexperienced listeners appeared to rely more heavily on pitch in making dissimilarity judgments than did experienced listeners. The resulting MDS representations of dissimilarity across pitch provide a glimpse of the timbre transformation of voice categories across pitch.

A Comparison of Two Methods of Formant Frequency Estimation for High-Pitched Voices

This study sought to compare formant frequencies estimated from natural phonation to those estimated using two methods of artificial laryngeal stimulation: (1) stimulation of the vocal tract using an artificial larynx placed on the neck and (2) stimulation of the vocal tract using an artificial larynx with an attached tube placed in the oral cavity. Twenty males between the ages of 18 and 45 performed the following three tasks on the vowels /a/ and /i/: (1) 4 seconds of sustained vowel, (2) 2 seconds of sustained vowel followed by 2 seconds of artificial phonation via a neck placement, and (3) 4 seconds of sustained vowel, the last two of which were accompanied by artificial phonation via an oral placement. Frequencies for formants 1-4 were measured for each task at second 1 and second 3 using linear predictive coding. These measures were compared across second 1 and second 3, as well as across all three tasks. Neither of the methods of artificial laryngeal stimulation tested in this study yielded formant frequency estimates that consistently agreed with those obtained from natural phonation for both vowels and all formants. However, when estimating mean formant frequency data for samples of large N, each of the methods agreed with mean estimations obtained from natural phonation for specific vowels and formants. The greatest agreement was found for a neck placement of the artificial larynx on the vowel /a/.

Can Listeners Hear Who is Singing? What is the Pitch Bandwidth of Singer Discrimination in Untrained Listeners?

OBJECTIVE/HYPOTHESIS This study sought to determine the pitch bandwidth of singer discrimination based on singer gender, pitch range, and same-different voice category. STUDY DESIGN Repeated measures factorial design. METHODS This study used a forced-choice paradigm, where listeners heard two different singers (singer 1 and singer 2) producing /ɑ/ at an identical pitch and an unknown singer (either singer 1 or singer 2) producing /ɑ/ at a different pitch. It was the listeners task to identify which singer (singer 1 or singer 2) was the unknown singer. Two baritones and two tenors were recorded producing /ɑ/ at the pitches C3, E3, G3, B3, D4, and F4. Two sopranos and two mezzo-sopranos were recorded producing /ɑ/ at the pitches C4, E4, G4, B4, D5, and F5. For each group of stimuli, male and female, all possible pairs of singers were constructed for the lowest pitch (C2 or C3, respectively) and highest pitch (F4 or F5, respectively). The unknown singer was varied across the remaining pitches. RESULTS For between category comparisons, the ability to discriminate singers diminished monotonically with pitch interval, reaching below chance levels between the intervals of the 9th and 11th. For within category comparisons, it was much harder to discriminate singers across pitch, particularly when the voices were female. CONCLUSION Timbre is not perceived as invariant across the entire singing range, and the bandwidth of this timbre invariance depends on multiple factors, including pitch range, gender, and same-different voice category.

The Traditional/Acoustic Music Project: A Study of Vocal Demands and Vocal Health

OBJECTIVE/HYPOTHESIS The Traditional/Acoustic Music Project seeks to identify the musical and performance characteristics of traditional/acoustic musicians and determine the vocal demands they face with the goals of (1) providing information and outreach to this important group of singers and (2) providing information to physicians, speech-language pathologists, and singing teachers who will enable them to provide appropriate services. STUDY DESIGN Descriptive cross-sectional study. METHODS Data have been collected through administration of a 53-item questionnaire. The questionnaire was administered to artists performing at local venues in Knoxville, Tennessee and also to musicians attending the 2008 Folk Alliance Festival in Memphis, Tennessee. RESULTS Approximately 41% of the respondents have had no vocal training, whereas approximately 34% of the respondents have had some form of formal vocal training (private lessons or group instruction). About 41% of the participants had experienced a tired voice, whereas about 30% of the participants had experienced either a loss of the top range of the voice or a total loss of voice at least once in their careers. Approximately 31% of the respondents had no health insurance. Approximately 69% of the respondents reported that they get their information about healthy singing practices solely from fellow musicians or that they do not get any information at all. CONCLUSION Traditional/acoustic musicians are a poorly studied population at risk for the development of voice disorders. Continued research is necessary with the goal of a large sample that can be analyzed for associations, identification of subpopulations, and formulation of specific hypotheses that lend themselves to experimental research. Appropriate models of information and service delivery tailored for the singer-instrumentalist are needed.

The effect of change in spectral slope and formant frequencies on the perception of loudness

OBJECTIVE/HYPOTHESIS This study attempts to understand how changes in spectral slope and formant frequency influence changes in perceived loudness. It was hypothesized that voices synthesized with steeper spectral slopes will be perceived as less loud than voices synthesized with less steep spectral slopes, in spite of the fact that they are of equal root mean square (RMS) amplitude. It was also hypothesized that stimuli with higher formant patterns will be perceived as louder than those with lower formant patterns, in spite of the fact that they are of equal RMS amplitude. STUDY DESIGN Repeated measures factorial design. METHODS For the pitches A3, C4, B4, and F5, three different source signals were synthesized with varying slopes of -9, -12, and -15 dB/octave using a frequency vibrato rate of 5.6 Hz and a frequency vibrato extent of 50 cents. Each of the three source signals were filtered using two formant patterns, a lower formant pattern typical of a mezzo-soprano (pattern A) and a higher formant pattern typical of a soprano (pattern B) for the vowel /a/. For each pitch, the six stimuli were combined into all possible pairs and normalized to equal RMS amplitude. Listeners were presented with 120 paired stimuli (60 pairs repeated twice). The listeners task was to indicate whether the first or second stimulus in the pair was louder. RESULTS Generally, as the spectral slope decreased, perceived loudness increased, with the magnitude of the perceived difference in loudness being related to the degree of difference in spectral slope. Likewise, at all pitches except A3, perceived loudness increased as formant frequency increased. CONCLUSION RMS amplitude is an important predictor of loudness perception, but many other factors also affect the perception of this important vocal parameter. Spectral composition is one such factor and must be considered when using loudness perception in the process of clinical diagnostics.