Modelling vocal-tract acoustics validated by flow experiments

Modelling the acoustic response of the vocal tract is a complex task, both from the point of view of acquiring details of its internal geometry and of accounting for the acoustic-flow interactions. A VOcal-tract ACoustics program (VOAC) has been developed [P. Davies, R. McGowan & C. Shadle, Vocal Fold Phys., ed. I. Titze, San Diego: Singular Pub., 93-142 (1993)], which uses a more realistic, aeroacoustic model of the vocal tract than classic electrical-analogue representations. It accommodates area and hydraulic radius profiles, smooth and abrupt area changes, incorporating end-corrections, side-branches, and net fluid flows, including turbulence losses incurred through jet formation. Originally, VOAC was tested by comparing vowel formant frequencies (i) uttered by subjects, (ii) predicted using classic electrical analogues, and (iii) predicted by VOAC. In this study, VOAC is further validated by comparing the predicted frequency response functions for a range of flow rates with measurements of the radiated sound from a series of mechanical models of unvoiced fricatives [C. Shadle, PhD thesis, MIT-RLE Tech. Rpt. 506 (1985)]. Results show VOAC is more accurate in predicting the complete spectrum at a range of flow rates. Finally, preliminary work is presented with VOAC used to simulate the sound generated at a sequence of stages during the release of a plosive