Tones in tonal languages are defined based on the characteristics of their fundamental frequencies. However, it has been shown that fundamental frequencies alone did not lead to good tone identification, both by human and machines. This paper reports a study based on tone perception experiments in which participants identified Thai tones from recorded mono-syllabic, bi-syllabic, and tri-syllabic stimuli as well as their modified counterparts. Stimuli were modified in various aspects so that effects of fundamental frequencies, syllable energy envelopes, and spectral shapes to tone perception can be observed. Results indicate that the spectral shape, especially in the vicinity of the first formant, contributes significantly to the participants' abilities to correctly identify tones and the contribution is more prominent with more syllables in the stimuli.

Index Terms: tone perception, Thai tones, formant frequencies, fundamental frequencies, pitches