Acoustic study of vowel nasalization in Thai

Abstract

Patterns of coarticulatory nasalization and segmental duration were investigated in Thai, a language with contrastive vowel length. Four Thai speakers produced multiple repetitions of real and nonsense CV(:)N items, where C=[b], V=/i e ae/, V:=/i: e: ae:/, and N=bilabial, alveolar, or velar nasal. Three temporal measures were taken: duration of V(:), N, and vowel nasalization. Acoustic onset of vowel nasalization was primarily identified from FFT spectra, sampled across the vowel in 10-ms increments, as onset of the nasal formant and/or broadening of formant bandwidth in the low-frequency region. Preliminary results from two speakers showed that long V: was nearly twice as long as short V, and final N was nearly two times longer following short V than long V: [A. S. Abramson, Int. J. Am. Linguist. 28 (1962)]. Vowel nasalization varied as a function of V(:)N duration: relative to N onset, nasalization started earlier in long V: than short V. However, long V: was proportionately less nasalized (44% for long V: vs 49% for short V). These results are compared to findings for English, and interpreted relative to look-ahead and coproduction models of coarticulation.