Effects of glottal and lip boundary conditions on vocal-tract area function estimates from speech signals

High-resolution vocal-tract area functions (VTAFs) can be derived from vocal-tract filters (VTFs) estimated from vowel sound signals with a wide bandwidth. However, the effects of open glottises and frequency-dependent lip reflection coefficients contained in the VTF estimates distort the VTAF estimates. Given VTF estimates obtained over closed glottal phases, we provide a method for eliminating the distortion effects of frequency-dependent lip reflection coefficients on the VTAF estimates. When the VTF estimates contain limited effects of incomplete glottal closures, this method can still obtain reasonable VTAF estimates if the vowel sounds are produced with large lip openings. The VTAF estimates obtained using our method from sounds /a/ produced by different subjects are very similar to that measured using the magnetic resonate imaging method. Theoretically, to eliminate both distortions caused by lip reflection coefficients and incomplete glottal closures in the VTAF estimates, lip-opening areas must be known.