Three approaches to the classification of American English diphthongs

Various investigations of diphthongs suggest that they can be effectively classified in terms of (1) the pattern of fundamental frequency and formants at the onset and offset of the production, (2) the onset formant pattern and the F2 rate of transition or (3) the onset formant pattern and the direction of formant movement in an acoustic space. These three hypotheses were assessed in (a) a log F1 × log F2 space and (b) an “auditory–perceptual space” in which the dimensions are based on ratios between pairs of formants and between F1 and a reference value related to the vowel’s average formant frequency. Values for relevant parameters were obtained for a corpus of 768 tokens of six American English diphthongs produced in two contexts ([b_d], [h_d]) at two tempos (slow, fast) with differing stress (stressed, unstressed). The hypotheses were evaluated in respect to classification performance using a statistical pattern recognition procedure. All three hypotheses produced correct classification of the corpus exceeding 90%, although highest correct classification was obtained by specification of onset and offset formant patterns (an average of 96%). Slightly higher percent correct classifications were obtained for each hypothesis when parameters are specified in the auditory–perceptual space rather than in the log F1 × log F2 space.