Say Ah: Identifying Voice Pathologies by Studying Harmonic to Noise Ratios

Speech pathologists study human voice production with a particular interest in understanding disorders and what might be done to prevent, cure, or alleviate the communicative problems such disorders might cause. This study is highly interdisciplinary and requires an understanding of the physics of sound production, the anatomy and physiology of vocal folds (or chords), clinical decision making, and the technological aspects of measuring and working with digital signal processing (the primary tool for representing voice).

Underlying all of these disciplines is, of course, applied mathematics. From the trigonometry of pure tones to Fourier analysis of complex sounds, and from measures of central tendency and simple inferential statistics to analysis of harmonic-to noise ratios, mathematical ways of thinking are inseparable from speech pathology. Often, basic principles of mathematics find new applications that lead to an increased understanding of the phenomenon being studied.

One contemporary example is the use Qi and Hillman (1997) have found for harmonic-to-noise ratios in the study of voice quality.