Lynn Maxfield

Intraoral pressures produced by thirteen semi-occluded vocal tract gestures

Abstract The use of semi-occluded vocal tract (SOVT) exercises as habilitative and rehabilitative tools has grown substantially in the past two decades. As the use of these exercises has grown, so too has the number of variations of the phonatory gestures used to create oral semi-occlusions. While much of the research on SOVT exercises to this point has been conducted using straw phonation, there has been little discussion or investigation regarding how other phonatory gestures that are considered to be SOVT compare to one another. The current study sought to measure the intraoral pressure produced by 13 phonatory gestures generally thought of as oral semi-occlusions. Twenty subjects (10 male, 10 female) produced three tokens of each gesture, and intraoral pressure was recorded via a thin, flexible-cannula pressure transducer. Pressures ranged between 0.1 and 1.0 kPa, but varied significantly between gestures and between subjects.

New Evidence That Nonlinear Source-Filter Coupling Affects Harmonic Intensity and fo Stability During Instances of Harmonics Crossing Formants

The traditional source-filter theory of voice production describes a linear relationship between the source (glottal flow pulse) and the filter (vocal tract). Such a linear relationship does not allow for nor explain how changes in the filter may impact the stability and regularity of the source. The objective of this experiment was to examine what effect unpredictable changes to vocal tract dimensions could have on fo stability and individual harmonic intensities in situations in which low frequency harmonics cross formants in a fundamental frequency glide. To determine these effects, eight human subjects (five male, three female) were recorded producing fo glides while their vocal tracts were artificially lengthened by a section of vinyl tubing inserted into the mouth. It was hypothesized that if the source and filter operated as a purely linear system, harmonic intensities would increase and decrease at nearly the same rates as they passed through a formant bandwidth, resulting in a relatively symmetric peak on an intensity-time contour. Additionally, fo stability should not be predictably perturbed by formant/harmonic crossings in a linear system. Acoustic analysis of these recordings, however, revealed that harmonic intensity peaks were asymmetric in 76% of cases, and that 85% of fo instabilities aligned with a crossing of one of the first four harmonics with the first three formants. These results provide further evidence that nonlinear dynamics in the source-filter relationship can impact fo stability as well as harmonic intensities as harmonics cross through formant bandwidths.

An Oral Pressure Conversion Ratio as a Predictor of Vocal Efficiency

Voice production is an inefficient process in terms of energy expended versus acoustic energy produced. A traditional efficiency measure, glottal efficiency, relates acoustic power radiated from the mouth to aerodynamic power produced in the trachea. This efficiency ranges between 0.0001% and 1.0%. It involves lung pressure and hence would appear to be a useful effort measure for a given acoustic output. Difficulty in the combined measurement of lung pressure and tracheal airflow, however, has impeded clinical application of glottal efficiency. This article uses the large data base from Schutte (1980) and a few new measurements to validate a pressure conversion ratio (PCR) as a substitute for glottal efficiency. PCR has the potential for wide application because of low cost and ease of use in clinics and vocal studios.

Gender differences and speech accommodation in occupational settings

Nearly one quarter of the U.S. workforce depends on a healthy, versatile voice as a tool for their profession. These are individuals who, lose voice quality and/or vocal endurance, would not be able to perform their job effectively. These occupational voice users include professionals such as teachers, counselors, emergency dispatchers, air traffic controllers, performers, and telephone workers. Women tend to have a disproportionate incidence of reported voice problems compared to men. They also make up the majority of several of these high voice-use occupations (e.g., public school teachers, call center workers). This presentation will provide an overview of our current understanding of gender discrepancy in vocal health issues as well as a discussion of recent results identifying underlying causes, which may contribute to their heightened risk. Such results include compensatory adjustments women use in different communication environments, speech accommodation to stress, and the relationship between voc...

The relation between choir size and choir dynamics

If six distinct levels of choir dynamics ( pp p mp mf f ff ) are to be achieved over two octaves of fundamental frequency in a choir section, how distinct are these levels? The just noticeable difference for sound level in a free field environment is 1-2 dB, while a doubling of loudness requires a 10 phon increase (10 dB SL increase at 1000 Hz). Most singers cannot double their vocal loudness 5 times. Generally the dynamic levels are 3–6 dB apart, depending on the individual voice range profiles of the singers. Overall choir size has no effect on dynamic range, unless the size is varied dynamically by not all singers singing all the time. A few loud voices dominate ff if everyone sings. To achieve an effective choir pp, only a few voices who can sustain very soft notes should sing. The dynamic range can be significantly limited when choral blend for loudness is imposed on a non-homogeneous group of singers.

Acoustic factors affecting the dynamic range of a choir

Based on the assumption that individual sound intensities of singers are incoherent and add linearly to produce a combined choir intensity, a model of a voice range profile of a choir is produced. It is shown that this model predicts six distinct levels of choir dynamics (pp p mp mf f ff) over two octaves of fundamental frequency in a choir section. The levels are 3-6 dB apart, depending on the individual voice range profiles of the singers. Overall choir size has no effect on dynamic range, unless the size is varied dynamically by not all singers singing all the time. For a non-homogeneousn group of singers, a few loud voices dominate ff if everyone sings, while pp is not achieved effectively without suppressing all voices that cannot sing soft. Furthermore, the dynamic range can be significantly limited when choral blend for loudness is imposed on a non-homogeneous choir.

A Formant Range Profile for Singers

Vowel selection is important in differentiating between singing styles. The timbre of the vocal instrument, which is related to its frequency spectrum, is governed by both the glottal sound source and the vowel choices made by singers. Consequently, the ability to modify the vowel space is a measure of how successfully a singer can maintain a desired timbre across a range of pitches. Formant range profiles were produced as a means of quantifying this ability. Seventy-seven subjects (including trained and untrained vocalists) participated, producing vowels with three intended mouth shapes: (1) neutral or speech-like, (2) megaphone-shaped (wide open mouth), and (3) inverted-megaphone-shaped (widened oropharynx with moderate mouth opening). The first and second formant frequencies (F1 and F2) were estimated with fry phonation for each shape and values were plotted in F1-F2 space. By taking four vowels of a quadrangle /i, æ, a, u/, the resulting area was quantified in kHz2 (kHz squared) as a measure of the subjects ability to modify their vocal tract for spectral differences.

Acoustic and perceptual differences between novice and professional music theatre singers

Research examining contemporary commercial music (CCM) styles of singing has increased significantly over the last ten years. While acoustic analysis has helped define which characteristics define various vocal genres, discrepancy still exists in how those acoustic characteristics are perceived, described, and evaluated. The current study recorded novice and professional musical theatre singers performing belt, legit, and mix vocal samples. Three acoustic analyses were applied to the excerpted recordings from each singer using the Praat voice and speech analysis software: The spectral slope of the long term average spectrum (LTAS) was calculated, as well as the noise to harmonic ratio (NHR), and the dominant harmonic (1st, 2nd, or 3rd) was noted for each sample. Results were compared across pitch, style (belt v. legit), and training level (professional v. novice). Finally, raters listened to the recordings and rated each sample on the basis of style (belt v. legit), roughness (rough v smooth), and tone qu...

Nonlinear dynamics helps explain how vowel influences register stability

Highly trained singers know what a registration shift feels like, where in their ranges it is likely to occur, and how to make small adjustments to make it less abrupt. They also know that the location of register changes differs depending on vowel choice and the style in which they are performing. Changing registers while singing can result in a significant timbral shift and, if approached unexpectedly, an abrupt jump in f o . If the source and filter interact in a purely linear fashion, f o should not be influenced by the shape of the vocal tract (vowel). This paper will demonstrate how nonlinear source-filter coupling may explain the strong relationship between vowel and registration. Eight volunteers performed f o glides while altering the dimensions of their vocal tracts, predictably changing the formant frequencies. It was hypothesized that if the source and filter operated as a purely linear system, f o stability should not be perturbed by formant/harmonic crossings in a linear system. Acoustic ana...

The effect of compromised pulmonary function on speech production among female school teachers

Females face a significantly higher risk than males of developing long-term voice problems with lifetime instances occurring in 46% of females compared to 37% of males. The higher incidence of prolonged problems among women has been associated with a number of gender differences, including physiological differences in the laryngeal system, differences in the endocrine system, and differences in pulmonary usage. Additionally, inefficient pulmonary utilization and reduced lung volume have been linked with vocal health concerns. Our study sought to use established spirometry measures and a relatively new questionnaire, the Vocal Fatigue Index (VFI), to determine if there is a relationship between pulmonary function and vocal fatigue among teachers. Additionally, if there is a relationship, to determine if that relationship is stronger in females than in males. 122 (96 females, 26 males) elementary and middle school teachers from the Jordan School District in northern Utah participated in this research. For f...