Formant frequency estimates for abruptly changing area functions: a comparison between calculations and measurements.

Vocal tract area functions may contain quite abrupt changes in cross-sectional area. In formant frequency calculations for such area functions, an inner length correction (ILC) should be applied. The relevance of this correction was investigated by comparing acoustic measurements obtained from a physical model of the vocal tract with data gathered by means of computer simulations. Calculating formant frequencies without applying internal length corrections caused substantial errors, particularly for area functions representing apical stops just anterior to occlusion. Decentering and axial symmetry in the arrangement of the area elements of the physical model were briefly studied and found to have effects on the formant frequency values.