On the Relationship between Formant Bandwidths and Vocal-Tract Shape Features
Lloyd Rice, Sven E. G. Öhman · The Journal of the Acoustical Society of America · 1974
Theoretical and experimental studies by Borg, Pinson, Schroeder, Mermelstein, and Heinz have demonstrated that the formant frequencies of vocalic speech sounds do not uniquely determine the area function of the vocal tract. For instance, a constant area function corresponding to an idealized neutral vowel can be perturbed in infinitely many ways without changing the formant frequencies, provided that the perturbing function is sufficiently “small” and is symmetric about the midpoint of the glottis-to-lip midline. It will be shown that the acoustic import of the frequency invariant perturbations is systematically reflected in the bandwidths of the formants. This claim will be supported by data collected from model experiments in which the pressure response at the lips to a velocity impulse excitation at the glottis is computed for a variety of vocal tract shapes and analyzed by means of the fast Fourier transform. The frequencies and bandwidths of the formants observed in the amplitude spectra thus computed are determined through an analysis-by-synthesis technique and related to certain features of the perturbations. The results shed some light on the possible role of the band-widths in speech perception.