Acoustic Phonetic Study on Lao Tones

MASUKO Yukie, SUZUKI Reiko

This study attempts to examine the acoustic phonetic characteristics of Lao tones not to show that five tones contrast to one another on equal terms, but to show hierarchical contrast.

In order to scrutinize acoustic characteristics reflecting tonal contrast in various phonemic environments, we selected a set of monosyllabic and disyllabic words. As to monosyllabic words, minimal pairs are selected differing only in tones. By combining two monosyllabic words, we made morpho-syntactic phrases showing all the possible twenty-five combination of tones. We also selected twenty-five disyllabic words that show tonal contrast between the first and the second syllable.

Comparison of pitch patterns of the first and the second monosyllabic word or those of the first and the second syllable of disyllabic words shows no “typical” tonal patterns. Instead, we found two major types in pitch curves, fall-rise type and (rise-) fall type. The former comprises the forth and the fifth, and the latter, the first, the second and the third tones. Within each type, contrast between ‘marked’ and ‘unmarked’ can be effectively observed. In the fall-rise type, the fifth tone is ‘marked’ showing the lowest F0 of the speaker during its pitch curve while the forth tone is ‘unmarked’. In the (rise-)fall type, the second and the third tones are ‘marked’ showing the steep fall in the latter half of the pitch curve while the first tone are ‘unmarked’.

Whereas the marked tones show their characteristics positively, the unmarked tones, when located next to the marked one, try to avoid showing characteristics similar to the marked one, by bearing their variant form to add some prominence to its adjacent marked one. We claim the variant forms cannot be explained in terms of coarticulatory perturbation since they are realized such as contour with 20 Hz higher depending on their tonal environments.

We observed that the fifth tone is the marked one compared with the fourth tone within the fall-rise type. Among (rise-)fall type tones, however, it is still not clear whether the ‘unmarked’ first tone contrasts with the ‘marked’ second and third tones, since between the second and the third tones, ‘markedness’ of each is unique to the tone and the one appears indifferent to the characteristic of the other’s, to which further consideration is necessary.