Vocal Instabilities in Untrained Female Singers.

Objectives: This study aimed to identify voice instabilities across registration shifts produced by untrained female singers and describe them relative to changes in fundamental frequency, airflow, intensity, inferred adduction, and acoustic spectra.

Study design: Multisignal descriptive study.

Methods: Five untrained female singers sang up to 30 repetitions of octave scales. They first produced these octave scales "naturally," followed by productions that were either deliberately smooth or deliberately unsteady. With all types of scale productions, participants sang with both /α/ and /i/ vowels, at two different dynamic levels, and across both the upper and lower predetermined register transitions. Recorded scales were categorized into three groups (Smooth, Middle, Unsteady) based on researcher-based perceptual smoothness of the auditory signals. These groups allowed for determination of salient features of unsteadiness based on observations and analyses of the acoustic, airflow, intensity, and electroglottography (EGG) waveforms.

Results: A total of 13 different types of instabilities were observed. The number of instabilities within a single scale ranged from zero to fourteen. Most Smooth scales had zero to three instabilities, most Middle scales had four to six, and most Unsteady scales had six or more instabilities within the scale. More obvious instabilities, such as aphonic segments, were present only in Unsteady scales, while more subtle instabilities, such as those related to EGG signal changes, were common in all scale categories, including Smooth scales.

Conclusions: This study revealed that untrained singers can sing smoothly throughout octave scales, and the primary unsteadiness variable was an aphonic segment and corresponding abrupt and large intensity reduction. Particular instabilities may be related to subtle aspects of register change and vocal control. Some objective measures appear to be more visually and numerically salient than auditorily perceived events relative to unsteadiness in the production of scales.