Time-varying features of initial stop consonants in auditory running spectra: A first report

Kewley-Port (1983) recently demonstrated that place of articulation of initial voiced stops could be identified from time-varying features observed in visual displays of linear prediction smoothed spectra. The present study extends this method of analysis in several directions. First, both voiced and voiceless syllable-initial stops produced at three speaking rates-normal, fast, and slow-were examined. Second, a new rule for vocal tract size normalization was tested. Third, the earlier time-varying features were augmented in order to specify the burst and voicing as well as place of articulation. The four time-varying features were (1) an abrupt increase in energy at high frequencies, (2) the onset of a prominent low-frequency peak, (3) the relative tilt of voiceless energy at onset, and (4) the presence of extended midfrequency peaks. Finally, the visual displays were modified to incorporate filtering and other characteristics of processing of speech by the auditory system. Auditory running spectra were generated for stop consonant-vowel syllables read by two males and two females. Employing the four time-varying features, judges first located the burst and onset of voicing, and then identified place of articulation from the visual displays. Over all conditions, place of articulation was identified at an 86% level of accuracy. While these results constitute only a first step towards an automated analysis procedure, they nonetheless indicate that our new time-varying features are appropriate for identifying place of articulation across both voiced and voiceless stops produced by different speakers at different speaking rates.