Journal of Speech and Hearing Research, Volume 35, 53-67, February 1992 Vocal Tract Area Function Estimation From Midsagittal Dimensions With CT Scans and a Vocal Tract Cast: Modeling the Transition With Two Sets of Coefficients Pascal Perrier Louis.Jean Bo6 Rudolph Sock Institut de la Communication Parle URA CNRS 368 INPG & Universit Stendhal Grenoble, France The generation of area functions from measurements of the sagittal section is an important step in the study of the relation between vocal tract geometry and speech acoustics. We present a new model to perform this transformation, inspired by the cAp model of Heinz & Stevens (1965). Our model is based on analysis of a vocal tract cast for large sagittal dimensions and for small sagittal dimensions on CT scans of the vocal tract constriction zones for the three cardinal vowels [i, a, ul of French. We extracted two sets of coefficients, appropriate for large and small sagittal dimensions respectively. We then compared the predictions of the model with those of other models from the literature. Finally, the usefulness of this dual coefficient procedure for the acoustic simulation of vowels was tested using sagittal sections generated by an acoustic model of the vocal tract. KEY WORDS: vocal tract modeling, vocal tract area function, vocal tract morphology, CT scans In speech production studies, the midsagittal section is one of the most convenient representations of articulatory data. This basic display has allowed many laboratories to refine their knowledge of articulatory phenomena in speech, and has been at the root of many articulatory models (see, in particular, Maeda, 1979; 1988). These models generate a midsagittal view from parameters associated with the lips, the tongue, the jaw, and the larynx (on this point see also Harshman, Ladefoged, & Goldstein, 1977; Lindblom & Sundberg, 1971). However, in order to study the relations between the geometry of the vocal tract and its acoustics, the midsagittal view must be transformed into an area function, which is the necessary input to an acoustic analog of the vocal tract. This area function represents thus a principled link in the transition from articulatory configurations to the acoustic output, and requires sufficient precision for its estimation. Unfortunately, such data cannot be obtained by direct measurements. Numerous studies on the midsagittai view of the vocal tract (see Dart, 1987, and Simon, 1967, for a historical review) prompted the development of X-ray techniques; however, there remains a relative scarcity of area function data. This explains the need for a model that converts the midsagittal dimensions of the vocal tract into area functions. This article presents and evaluates a model we have developed to accomplish this 0 1992, American Speech-Language-Hearing Association 53 0022-4685/92/3501 -0053$01.00/0