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Physics of Voice Production
Neuromuscular control of voice
Production and perception
Mechanical models of voice production
Computational models of voice production
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Characterization of the three-dimensional glottal flow field and its acoustical relevance
The glottal flow contains the sound source information which is eventually radiated into the speech signal we hear. The goal is to 1) identify the flow features that are important to voice production, and 2) to understand how these flow features vary at different laryngeal/voice conditions. To achieve this goal, we use several models of vocal fold vibration, including driven physical models, self-oscillating physical models, and excised human larynx models in our laboratory. The glottal flow field is quantified using high-speed 3D Digital Particle Imaging Velocimetry (DPIV).
In a first study (Neubauer et al., 2007), we measured the near field flow structures immediately downstream of a self-oscillating, physical model of the vocal folds, with a vocal tract attached. A spatio-temporal analysis of the structures
was performed using the method of empirical orthogonal eigenfunctions. Some of the observed flow structures included vortex generation, vortex convection, and jet flapping. Jet flapping was observed, presumably due to antisymmetric
(staggered) arrays of large-scale vortices in the streamwise direction in the turbulent region. In the transition region of the glottal jet, large-scale vortices were generated, presumably from the growing instability waves in the free shear layer surrounding the laminar core region.
In another study (Zhang and Neubauer, 2010) we attempted to experimentally quantify the influence of supraglottal flow structures on phonation by disturbing the supraglottal flow field with a cylinder and observing the consequences on vocal fold vibration and sound production. The hypothesis is that if the supraglottal flow structures are essential to the production of the low-frequency harmonic component of voice, significant changes in the low-frequency sound should be observed if these supraglottal flow structures are significantly altered. Our results showed little influence of the presence of the cylinder on phonation despite a significantly altered supraglottal flow field. This indicates that the many complex supraglottal flow structures (vortical structures, jet flapping, and turbulence) may only play a minor role in normal phonation. For practical applications, this suggests that a glottal flow model can be developed with reduced complexity but still capable of predications of reasonable accuracy, thereby significantly reducing computational cost.
Indeed, our numerical model based on a linear stability analyis and a one-dimensional flow model (Zhang et al., 2007; Zhang and Luu, 2012) has been very successful in qualitatively predicting experimental observations in physical model experiments regarding the dependence of phonation threshold pressure on vocal fold geometry and stiffness (Mendelsohn & Zhang, 2011; Zhang, 2010) and left-right difference in vibration amplitude and phase in left-right asymmetric vocal fold conditions (Zhang & Luu, 2012).
Neubauer, J., Zhang, Z., Miraghaie, R., Berry, D.A. (2007). Coherent structures of the nearfield flow in a self-oscillating physical model of the vocal folds, J. Acoust. Soc. Am., 121(2), 1102-1118. [pdf] [link]
Zhang, Z., Neubauer, J., Berry, D.A. (2007). Physical mechanisms of phonation onset: a linear stability analysis of an aeroelastic continuum model of phonation, J. Acoust. Soc. Am., 122(4), 2279-2295. [pdf] [link]
Zhang, Z. (2010). Dependence of phonation threshold pressure and frequency on vocal fold geometry and biomechanics, J. Acoust. Soc. Am., 127(4), 2554-2562. [pdf] [link]
Zhang, Z., Neubauer, J. (2010). On the acoustical relevance of supraglottal flow structures to low-frequency voice production, J. Acoust. Soc. Am., 128(6), EL378-EL383. [pdf] [link]
Mendelsohn, A., Zhang, Z. (2011). Phonation threshold pressure and onset frequency in a two-layer physical model of the vocal folds, J. Acoust. Soc. Am., 130, 2961-2968. [pdf] [link]
Zhang, Z., Luu, T.H. (2012). Asymmetric vibration in a two-layer vocal fold model with left-right stiffness asymmetry: Experiment and simulation, J. Acoust. Soc. Am., 132, 1626-1635. [pdf] [link]
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