In order to produce sound with these aerophones, the player makes a ribbon-shaped flow of air with their lips (421.1), or their breath is directed through a duct against an edge (421.2).
421.1 Flutes without duct – The player creates a ribbon-shaped stream of air with their lips.
421.11 End-blown flutes – The player blows against the sharp rim at the upper open end of a tube.
421.12 Side-blown flutes – The player blows against the sharp rim of a hole in the side of the tube.
421.121.12 With fingerholes 421.121.2 Partly stopped side-blown flutes - The lower end of the tube is a natural node of the pipe pierced by a small hole.
421.121.311 With fixed stopped lower end - (Apparently non-existent).
421.121.312 With adjustable stopped lower end 421.121.32 With fingerholes.
421.13 Vessel flutes (without distinct beak) The body of the pipe is not tubular but vessel-shaped.
This group includes flutes with the duct formed by an internal baffle (natural node, bock of resin) and an exterior tied-on cover (cane, wood, hide).
421.222.12 With fingerholes 421.222.2 Sets of partly stopped flutes with internal duct.