Compound tones also occur: A falling tone is a combination of a high and a low toneme; a rising tone is a combination of a low and a high toneme. Compound tones are always analyzable, either synchronically or diachronically, and never contrast with single tones in lexical or grammatical semantics.
Source: nd
Source: Meeuwis 1998: 9
Source: Meeuwis 1998: 9