A fipple is a constricted mouthpiece common to many end-blown flutes, such as the tin whistle and the recorder. These instruments are known variously as fipple flutes, duct flutes or tubular-ducted flutes.

For example, in a recorder, a wooden fipple plug, with a ducted flue windway above it in the mouthpiece of the instrument, compresses the player's breath so that it travels along the windway. Exiting from the windway, the breath is directed against a hard bladed edge called a labium lip. The air flowing over the voicing mouth creates a flow-controlled valve, or 'air reed'. Interaction between the air reed and the air column in the body of the instrument excites standing waves in the air column, which determines the pitch of the sound. This oscillation results in the whistle sound in ducted flue instruments.

A distinct tone colour, determined by the dimensions of the instrument and the voicing mouth, is then slightly modified by the player's technique or embouchure. In instruments such as the recorder, the player can vary the pitch of the resulting musical note by opening or closing finger holes along the bore of the instrument, thus changing the effective length.