Sensitivity of Source-Filter Interaction to Specific Vocal Tract Shapes.

A systematic variation of length and cross-sectional area of specific segments of the vocal tract (trachea to lips) was conducted computationally to quantify the effects of source-filter interaction. A one-dimensional Navier-Stokes (transmission line) solution was used to compute peak glottal airflow, maximum flow declination rate, and formant ripple on glottal flow for Level 1 (aero-acoustic) interactions. For Level 2 (tissue movement) interaction, peak glottal area, phonation threshold pressure, and deviation in fo were quantified. Results show that the ventricle, the false-fold glottis, the conus elasticus entry, and the laryngeal vestibule are the regions to which acoustic variables are most sensitive. Generally, any narrow section of the vocal tract increases the degree of interaction, both in terms of its length and its cross-sectional area. The closer the narrow section is to the vocal folds, the greater the effect.