An acoustical study of American English diphthongs.

English diphthongs are usually produced with more than one vocal tract shape. This study attempts to collect acoustical data of English diphthongs published by Hillenbrand et al. (1995) online and to examine acoustic features of the diphthongs for phoneticians and English teachers. 63 American males and females were chosen after excluding those subjects with different target vowels or ambiguous formant tracks. The author used PRAAT to obtain the acoustical data systematically at 11 equidistant timepoints over the diphthongal segment. Results show that the formant trajectories of the diphthongs produced by the American males and females appeared quite similar. When the female formant values were uniformly normalized to those of the males, almost a perfect collapse occurred. Second, the diphthongal movements on the vowel space appeared not linear due to the coarticulatory gesture for the following consonant. Third, the average duration of the diphthongs produced by the females was 1.156 times longer than that of the males while the pitch ratio between the two groups turned out to be 1.746 with a similar contour over measurement points. The author concludes that English diphthongs produced by various groups can be compared systematically when the acoustical values are obtained at proportional timepoints.