Biophysics of Vocal Production in Mammals

Abstract

Most mammals, including humans, produce sound in agreement with the myoelastic-aerodynamic theory (MEAD): by converting aerodynamic energy into acoustic energy via flow-induced self-sustaining oscillation of the vocal folds or other laryngeal tissue. The generated laryngeal sound is filtered by the vocal tract and radiated from the mouth and/or the nose. In this chapter, some basic biophysical principles of the MEAD theory are explained, mostly based on research done in humans. Empirical evidence and concepts for nonhuman mammals are provided when available and applicable. In particular, biomechanical properties of vibrating laryngeal tissue and respective vibratory modes are described, and the oscillatory components and forces necessary for flow-induced self-sustaining vibration are discussed. The notions of fundamental frequency and its control, periodicity, and irregularity are explored, followed by a basic description of nonlinear phenomena (NLP) such as bifurcations, subharmonics, or chaos. Subglottal pressure and glottal airflow are essential parameters of voice production, and their influence on the generated voice source spectrum is considered. Finally, linear and nonlinear effects of the vocal tract are reviewed, and the efficiency sound production is discussed.