Voice register in Khmu': experiments in production and perception.

Some Khmu' dialects have phonologically distinctive voice registers. Auditory observations have claimed a stable distinction between clear voice and high pitch for Register 1 and breathy voice and low pitch for Register 2 in the Khmu' Rawk dialect of northern Thailand. Word pairs distinguished only by register were recorded by 25 native speakers. Acoustic analysis yielded F0 and overall amplitude contours, frequencies of F1 and F2 in quasi-steady states of the vowels, relative intensities of higher harmonics to that of the first harmonic, and vowel durations. When circumstances caused early attention to perception testing, the words of only 8 speakers had been analyzed for properties other than amplitude and F0. Since the only significant factor that had emerged by then was F0 contour, the synthetic stimuli were made with just a series of seven contours. The labeling by 32 native speakers yielded two categories, demonstrating the sufficiency of F0 as an acoustic cue. The completed acoustic analysis showed a significant effect of one of the harmonic ratios for the women only, suggesting a conservative bias. The language has been shifting toward tonality and may have reached it.