Nonlinear Acoustic Analysis of Voice Production

Abstract

Voice production involves motion of the vocal folds, which act as a pair of coupled oscillators. Specifically, the vocal folds and glottal airstream form a mechanical system, where energy from the airstream can be imparted to the vocal fold tissue; with enough energy, the vocal folds will begin to self-oscillate and columns of air will pass through the glottis, creating phonation. The signal produced by this airflow is then filtered by the vocal tract and heard as voice. Supraglottic structures such as the supraglottic larynx, lips, tongue, palate, pharynx, and nasal cavity then act as resonators to produce the sound that is heard as voice. Small changes in supraglottic structures can affect voice quality. The voice signal produced through vocal fold oscillation is modulated by other sources of internal motion such as respiration, heartbeat, action potentials, and air turbulence, as well as sub- and supraglottal anatomical structures. Evaluating the quality of voice is an important aspect of vocal health assessment as it is a simple and noninvasive method for judging the outcomes of surgical procedures and following someone’s progress over the course of therapy. Two main options for analyzing a voice are through perceptual methods and computational signal processing.