Non-linear dynamics in mammalian voice production

Abstract

Animal vocalizations range from tonal sounds to irregular atonal sounds and are generated from non-linear oscillations of the vocal folds as well as from turbulent noise in the glottis. Comprehensive study on bioacoustic signals indicates the existence of a diversity of non-linear phenomena, such as limit cycles, subharmonics, biphonation, chaos, and bifurcations in animal vocalizations, which may provide keys to understanding animal communications. In this paper, we review the concept of nonlinear dynamics and its methodology as applicable to bioacoustics. Acoustical analysis of recorded sounds, simulation of a biomechanical model of the voice production system, and physical experiment of the vocal tract and vocal folds are presented to demonstrate non-linear features inherent in animal vocalizations. We focus on source–filter interaction as one of the main regulators of the non-linear property that can lead either to efficient vocalization or to voice instability in animal sounds. A combination of different approaches is suggested to be of great use for extracting the essential features of non-linear dynamics in animal vocalizations.