On direct aeroacoustics calculations of the vocal tract

Authors: Schickhofer, L., Dahlkild, A. A., Mihaescu, M
Document Type: Conference
Pubstate: Accepted
Journal: Proceedings of the 11th ERCOFTAC Workshop on Direct and Large-Eddy Simulation
Year: 2017


Voice production and the verbal expression by speech are crucial components of human communication. The human voice is not just conveying information directly through words, but also indirectly as paralinguistic information such as the speaker's emotional state through tonality. As such voice is generated through a two-part process: First, a source signal is produced by the vocal folds that are pulsating the lung pressure and volumetric flow rate in a particular frequency through periodic opening and closing. Second, the vocal tract causes an attenuation or amplification of this source signal at certain frequencies depending on its specific shape. The voice generation process can therefore be described by a source-filter model with the vocal folds acting as the source and the vocal tract as an acoustic filter. Thus, we are able to produce different vowels and sounds as we manipulate the vocal tract during phonation. However, the ability to speak can be compromised due to clinical conditions affecting the opening between the vocal folds (i.e. glottis) or the vocal tract. Certain voice disorders such as partial or total vocal fold paralysis and laryngeal cancer are known to affect the source signal and its waveform considerably. Nevertheless, the actual cause-effect relations between physiological changes in the vocal tract on the far-field acoustic pressure are unclear. An additional factor in voice production is the shedding of intraglottal vortical structures. The sound output generated by vortices becomes important in cases of incomplete glottal closure or paralysed vocal folds. However, its overall effect on the propagated acoustic signal has not been quantified yet. By varying parameters of the glottal waveform such as base frequency and glottal opening quotient, their impact on the formant positions, voice loudness, and intelligibility, as well as flow instabilities is assessed. This further develops the knowledge of cause-effect relations in phonation and opens up new therapeutic options for vocal tract disorders. Answering this research question will be essential for the advancement of therapeutic methods and targeted therapy when dealing with patients suffering from vocal tract disorders.