T. V. Ananthapadmanabha
Voice and Speech Systems, 53, ``Girinivas,'' Temple St., Malleswaram, Bangalore 560 003, India
Quantal theory of Stevens [J. Phonetics 17, 3--45 (1989)] states that there appear to be ranges of the articulatory parameter for which there is very little change in the acoustic parameter and other ranges where the acoustic parameter is more sensitive to changes in articulation. This result has been arrived at using a three- or four-tube model and coupled resonator theory. In this paper, the above experiment is replicated using a more realistic frequency domain method for calculating the formant frequencies for a given area function which include the effect of yielding walls and radiation impedance. Further, the quantal theory of vowel production is studied using Steven's and Mermelstein's articulatory models. Nomograms have been generated for these models. The acoustic and perceptual effects of perturbing articulatory parameters centered around the target values for selected vowels are studied. Preliminary experiments show that (a) the so-called areas of stability (broad F2 maximum, F3 minimum) are, in fact, most sensitive for articulatory changes and (b) for a given change in articulation, while F2 is insensitive, F1 and/or F3 are highly sensitive. In view of these findings, the quantal theory may have to be restated.