15th International Congress of Phonetic Sciences (ICPhS-15)
Tone in Vietnamese is usually equated to pitch. There are eight tones in standard North Vietnamese: ngang (high level), huyen (low level), sac1 (rising), nang1 (dropping), nga (broken), hoi (falling-rising), sac2 (rising, short), and nang2 (falling, short). Phonologically, these tones are said to fall into two registers: high (ngang, sac1, hoi, and sac2) and low (huyen, nang1, nga, and nang2). However, there is a serious mismatch: phonologically, hoi is high but, phonetically, it is low, and nga, is the opposite, phonologically low but phonetically high. Experimental evidence from an acoustic study that examined phonation types shows that breathiness and creakiness rather than pitch height are the primary perceptual cues of tone. This study resolves the apparent anomaly with hoi and nga and casts serious doubts on the simple equation of tone to pitch.
Bibliographic reference. Pham, Andrea Hoa (2003): "The key phonetic properties of vietnamese tone: a reassessment", In ICPhS-15, 1703-1706.