Tracing the mechanisms that generate tonal content in voiced speech

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Voice disorders are of high social and economic relevance as it affects many people in our society. Consequently, concerned patients suffer from increased physiological and psychological stress as reduced quality of life.The normal voice of a healthy human is the result of a complex fluid-structure-acoustic interaction. The structural motion of the vocal folds intensely modulates the flow through the glottis, which generates the main portion of the sound. Thereby, normal and healthy phonation is characterized by a strong harmonic content. The vocal tract downstream of the vocal folds is a key factor for acoustic back-coupling on the vocal fold motion as well as the flow. Hence, in addition to creating formants, we hypothesize that the vocal tract also impacts the generation of higher harmonics in the resulting voice signal, which is crucial for a healthy voice. The central objective of the research project is to advance the understanding of tonal sound generation during phonation based on a fully-coupled experimental investigation of the underlying mechanisms. The experimental setup in our laboratory replicates the fully-coupled phonation process in a well-established larynx model. We aim to further extend its functionality by integrating geometry-variable simplified channels as well as an MRI-based vocal tract shape for experiments. This enables us to separately investigate the different mechanisms during phonation as influenced by a vocal tract. The project incorporates three innovative aspects. (1) The focus is set on the harmonic content and acoustic back-coupling in a fully-coupled experimental approach that represents the basic mechanisms of the phonatory process. (2) With our state-of-the-art PIV-based technique, a direct experimental determination of the acoustic source field and sound radiation is enabled. (3) A comprehensive description of the vocal fold motion and its structure interaction is generated by laser vibrometer measurements with a strong focus on its harmonic content, as well.Finally, this yields the mechanisms responsible for harmonic sound generation, which interacts with back-coupling of the vocal tract.