What are contour tones in Hmong-Mien languages?

In the context of Hmong-Mien languages, contour tones are tones characterized by a change in pitch during the production of a syllable. Unlike level tones, which maintain a relatively steady-state pitch, contour tones involve pitch movements such as rises, falls, or more complex patterns like rise-falls.12

These tones are a fundamental component of the phonology of Hmong-Mien languages, where they contribute to word identification alongside consonants and vowels. Some languages within this family, such as Longmo Bunu and Zongdi Hmong, feature large and complex tonal inventories that include both level and contour tones. While some Hmong-Mien languages are noted for having a high number of level tone distinctions, the presence of contour tones is a defining feature of many languages in Southeast Asia.12