Contextual Variation of the Vowel Voice Source as a Function of Adjacent Consonants

The contextual effects of voiced/voiceless stops on the voice source of an adjacent vowel were examined for the first vowel in 'CVCV utterances in German, English, Swedish, French, and Italian. The principal analysis technique involved interactive inverse filtering and parameterisation of the glottal waveform in terms of a four-parameter voice source model (the LF-model). This analysis procedure was supplemented by measures from narrow-band spectral sections of the speech output and by oral airflow recordings which allow inferences about the relative timing of glottal and supraglottal gestures. Results indicated that the voiced/voiceless nature of the consonant does yield differences in the voice source of the vowel. The most striking effects were found in the context of voiceless consonants, and cross-language differences did emerge in terms of directionality and degree. Extensive anticipatory effects were found for Swedish and for some speakers of English. Preceding the voiceless stop the vowel becomes increasingly breathy-voiced, and it would appear that the glottal abduction gesture is anticipated very early in the course of the vowel. Italian exhibited a similar tendency, though to a considerably lesser degree. The German data, on the other hand, showed certain strong carryover effects: Following the voiceless aspirated stop there was extensive breathy voicing. French showed little contextual variation in either direction. Rather surprisingly, the observed effects were not directly correlated with, or predictable from, the phonetic categories involved (voiced, voiceless unaspirated, and voiceless postaspirated). These results yield insights into the control parameters which may be involved in regulating voicing oppositions in these languages. Whereas the anticipatory effects observed might be consistent with a "timing" model of glottal control, the carryover effects cannot be explained in terms of timing alone and suggest that differences in tension settings of the laryngeal musculature may also be implicated.