Jan P. H. van Santen
John S. Coleman
Mark A. Randolph
AT&T Bell Labs., 600 Mountain Ave., P.O. Box 636, Murray Hill, NJ 07974-0636
Studies of the effects of contextual factors on segmental duration have been mostly restricted to overall duration and relatively few have paid attention to the internal time course of speech segments. However, fine-grained temporal analysis of speech segments is hindered by within-speaker variability and the unreliability of manual segmentation. In this paper, using new methods for reducing statistical ``noise'' in acoustic trajectories [mappings of the time domain into an appropriate acoustic parameter space, such as formants, cepstra, etc.], analyses are presented of the effects of postvocalic voicing on the internal time course of selected vowels and diphthongs preceding voiced and voiceless consonants in contrasting minimal word pairs [e.g., ``mend'' versus ``meant''] are presented. These methods include the computation of the centroid of a set of acoustic trajectories, the average of a set of time warps among minimal word pairs, and various smoothing techniques. The centroid trajectories of a minimal pair generally coincide closely. It was found that lengthening due to postvocalic voicing is nonuniform, with certain regions expanding more than others. The location of maximal expansion could be determined reliably in most vowels and diphthongs studied, and, except for /a[sup y]/, occurs towards the end of the vowel or diphthong. For /a[sup y]/, the maximal expansion occurs toward the beginning of /a/.