Syllable structure and its acoustic effects on vowels

Vowel devoicing is a common phonological process in many languages and typically involves high vowels and schwa. High vowels and schwa are inherently short (Bell, 1978; Dauer 1980) and the process usually occurs when the vowels are either adjacent to, or surrounded by, voiceless consonants, during which the glottis is fully open. It is thought that vowel devoicing is a consequence of articulatory undershoot of the glottal movements. It also suggests that vowel devoicing processes are the results of the glottal gestural overlap between voiceless consonants and short vowels. The movements of glottal muscles for the short high vowels /i/ and /u/ blend with those of the adjacent voiceless sounds or a pause (Jun, 1993; Jun and Beckman, 1994). In many languages, the process is also considered to be part of the vowel neutralization and reduction processes in which vowels are first reduced in duration and centralized in quality, typically in the unaccented position, and then eventually devoiced and/or deleted in fast or casual speech (Hyman 1975, Wheeler 1979, Dauer 1980, Kohler 1990).