ACOUSTIC COUPLING IN PHONATION AND ITS EFFECT ON ...

3methods incorrectly suppress ripples during the closed phase and distort the glottalairflow estimates due to subglottal coupling. This type of tract coupling has not beenexplored in the context of inverse filtering before.A different type of inverse filtering technique can be implemented through accelerationmeasured on the skin overlying the suprasternal notch to obtain estimates ofglottal parameters [35–38]. This technique has been shown of great importance forthe ambulatory assessment of vocal function. This subglottal inverse filtering requiresa different approach, as zeros are present in its impedance, making standard vocaltract based methods unapplicable. In addition, the acoustic coupling between thesubglottal system and the vocal tract is expected to be more pronounced in this casedue to the much larger impedance of the latter. Initial efforts have indicated thatthe estimation of glottal parameters by means of inverse filtering via the subglottalsystem is possible [35]. However, these attempts were limited by the partial understandingof the underlying physical phenomena and the factors that could distortthe estimates. Among them, the effects of incomplete glottal closure were suggestedto increase the acoustic coupling with the vocal tract and thus distort the estimatesof glottal airflow. The appropriate way to handle the coupling effects and obtainestimates of the “true glottal source” in this case thus remain unexplored.Incomplete glottal closure has been shown to be common in normal and disorderedvoices [25, 26, 39], and female voices can have no glottal contact at all [12, 13, 40].However, there have been only a few studies on the effects of incomplete closure onthe vocal folds dynamics. Only recently the influence of a posterior gap on the airflowand its net energy transferred was investigated using a driven synthetic model [41].However, no theoretical or numerical studies have explored the effects the incompleteclosure on the tissue dynamics and energy transfer. Further understanding of theunderlying physical phenomena during incomplete glottal closure can impact inversefiltering studies.The governing principles of acoustic interaction and its implications on the inversefiltering of speech sounds obtained from both oral airflow and neck surface acceler-