A phonetic study of nasals and nasalization in Hong Kong Cantonese

Abstract

Nasal speech sounds occur in most of the world's languages (Maddieson, 1989). In Hong Kong Cantonese (HKC), seven long vowels [i, y, E, a, a, 3, u] and four short vowels [ I , e, e, u] can occur in a closed syllable with a nasal ending, i.e. [m, n, q]. Three objectives were pursued in this study. The first deals with the use of nasal and oral masks with a microphone for recording the nasal and oral airflows and analyzing the aerodynamic properties, including the airflow volume, rate/velocity, and duration for the nasals and the nasalized vowels in HKC with the help of a wideband spectrogram. The second was the investigation of the spectral properties of the nasalized vowels in the production of the CVN or CVN monosyllables. And, the last was the testing of the aerodynamic approach for determining the reduction in duration and nasal properties for the nasals and nasalized vowels in the bisyllables, compared to the monosyllables in HKC. Various methodologies have been employed for investigating the nasals and nasalization in different languages. One of the aims of this study was to determine the practicality of the airflow recording for gathering information about the phonetic correlates of nasality in speech as opposed to other previous methods. The PCquirer multi-channel acquisition system fitted with oral and nasal masks was chosen for airflow recording, simultaneously with the recording of speech signals. The nasal and oral airflow data were interpreted with reference to the waveform and wideband spectrogram. Airflow recordings for the four HKC speakers in their early twenties show that i) the percentage of vowel nasalization, i.e., the duration of the simultaneous occurrence of oral and nasal airflow during the acoustic period of the vowel in proportion to the overall vowel duration, and ii) the percentage of nasal airflow duration, i.e., the duration of vowel nasalization in proportion to the total duration of the nasal airflow, can act as an algorithm for quantifying the extent of nasality for different nasalized vowels in different nasal contexts. Based on the two percentage measurements made in this study, the long vowels are found to be more nasalized than short vowels. In addition to the vowel length effect, vowel height also has an effect the vowel nasality, with low vowels being more nasalized than the mid and high vowels. Tone type as well as the type of nasal ending trigger a slight effect on the nasalized vowel, with long vowels generally having a greater nasality in the context of [g] than in other two nasal contexts [m, n], especially when associated with the level tones, i.e., [55, 33,221. Some of these findings are in agreement with previous perceptual and physiological findings by other authors. However, the distribution of vowel and nasal nasality in the CV:N or CVN monosyllables has been found to be different in bisyllabic compounds production. The durations of the component segments, i.e., V and N, of a CVN syllable are much reduced in the bisyllables as opposed to the monosyllables. The duration reduction for the vowels is obvious in the presence of a long high vowel in the context of [m], while nasal duration reduction is obvious in the presence of a long low vowel in the context of [מ]. The production strategies for temporal reorganization of the component vowel and nasal of a bisyllable as opposed to a monosyllable are complex and speaker-independent. In addition to aerodynamic analysis, another approach is used for the analysis of the acoustics of vowel nasalization in HKC, by investigating the spectral properties of nasalized vowels at two different portions, both the non-nasalized and the nasalized portions, in comparison with their oral counterparts. As it is well known that the nasal tract configuration varies according to the speaker, speakers of HKC do not have to maintain the orality of oral vowels as strongly as they can, because of the lack of contrastive distinction between oral and nasal vowels in HKC. In general, the acoustic manifestation of nasal coupling depends mostly on the identity of the vowel to be nasalized, instead of other factors such as nasal contexts. It is possible to identify and describe different types of spectral modifications of all the vowels in HKC by focusing on the distribution of vowel formant frequencies. As for the contribution of the thesis, the main results obtained from the aerodynamic investigation are calibrated which in turn facilitate the cross-linguistic and cross-speaker comparisons upon the study of vowel nasalization. The aerodynamic studies were conducted with a vast language material for investigating the effect of all different vowel types and nasal endings on the vowel nasalization. It is an in-depth study of the phonetic properties, in terms of the aerodynamic, temporal and spechal characteristics, of the vowel nasalization in HKC. Besides, it helps develop and determine the phonetic correlates of nasality, in terms of (i) nasal airflow volume (Chapter 2), (ii) nasal airflow duration (Chapter 3) and (iii) nasal airflow rate (Chapter 4), for further perceptual study of vowel nasalization in HKC and other Chinese dialects in the future.