Chin music = mouth music. Known in Gaelic speaking Scotland as Port-a-beul, and in Ireland as lilting, jigging, gob-music or puss-music.
It is the singing of dance tune tunes using vocables.
Used as a memory aid for musicians, but has become an art in itself and has been used for dancing to, especially when there were no instruments available. This was particularly useful during the times in Ireland when the church took against traditional music and dancing and broke up house and crossroads dances, often smashing or confiscating the instruments.
Possibly the highest form of mouth music in Scotland was canntaireachd, used for remembering pipe tunes
Jim Carroll