The player makes a ribbon-shaped flow of air with his/her lips [421.1] or his/her breath is directed through a duct against an edge [421.2].

421.1 Flutes without duct – The player himself/herself creates a ribbon-shaped stream of air with his/her lips.

421.11 End-blown flutes – The player blows against the sharp rim at the upper open end of a tube.

421.111 Individual end-blown flutes.
421.111.1 Open single end-blown flutes – The lower end of the flute is open.

421.111.11 Without finger holes.
421.111.12 With finger holes.
421.111.2 Stopped single end-blown flutes – The lower end of the flute is closed.

421.111.21 Without finger holes.
421.111.22 With finger holes.

421.112 Sets of end-blown flutes or panpipes – Several end-blown flutes of different pitch are combined to form a single instrument.
421.112.1 Open panpipes.
421.112.11 Open or raft panpipes – The pipes are tied together in the form of a board, or they are made by drilling tubes in a board.
421.112.12 Open bundle or panpipes – The pipes are bundled together to form the instrument.
421.112.2 Stopped panpipes.
421.112.3 Mixed open and stopped panpipes.
421.12 Side-blown flutes – The player blows against the sharp rim of a hole in the side of the tube.

421.121 Single – side-blown flutes.
421.121.1 Open – side-blown flutes.
421.121.11 Without finger holes.
421.121.12 With finger holes – Western concert flute.
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.

421.121.3 Stopped side-blown flutes.
421.121.31 Without finger holes.
421.121.311 With fixed stopped lower end – [apparently non-existent].
421.121.312 With adjustable stopped lower end – piston flutes.
421.121.32 With finger holes.
421.122 Sets of side-blown flutes.

421.122.1 Sets of open slide-blown flutes.
421.122.2 Sets of stopped side-blown flutes.
421.13 Vessel flutes [without distinct fipple] – The body of the pipe is not tubular but vessel-shaped – Xun.

421.2 Flutes with duct or duct flutes – A narrow duct directs the air-stream against the sharp edge of a lateral orifice.
421.21 Flutes with external duct – The duct is outside the wall of the flute; this group includes flutes with the duct chamfered in the wall under a ring-like sleeve and other similar arrangements.

421.211 Single flutes with external duct.
421.211.1 Open flutes with external duct.
421.211.11 Without finger holes.
421.211.12 With finger holes.
421.211.2 Partly stopped flutes with external duct.
421.211.3 Stopped flutes with external duct.
421.212 Sets of flute with external duct.

421.22 Flutes with internal duct – The duct is inside the tube. 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).

421.221 Single flutes with internal duct.
421.221.1 Open flutes with internal duct.
421.221.11 Without finger holes – Whistle.
421.221.12 With finger holes – Recorder.
421.221.2 Partly stopped flute with internal duct.
421.221.3 Stopped flutes with internal duct.
421.221.31 Without finger holes.
421.221.311 With fixed stopped lower end.
421.221.312 With adjustable stopped lower end.

421.221.4 Vessel flutes with duct.
421.221.41 Without finger holes.
421.221.42 With finger holes – Ocarina.
421.222 Sets of flutes with internal duct.
421.222.1 Sets of open flutes with internal duct.
421.222.11 Without finger holes – Open flue pipes of the pipe organ.
421.222.12 With finger holes – Double flageolet.
421.222.2 Sets of partly stopped flutes with internal duct.
421.222.3 Sets of stopped flutes with internal duct.

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