The recorder is a woodwind instrument that belongs to the group of longitudinal flutes. To generate sound, its head contains a core made of wood or plastic, which only leaves a narrow gap (the core gap) free. Recorders are usually made up of three parts and consist of a head piece, middle piece and foot piece. Sopranino, soprano and alto recorders are also built in two parts, with the middle and foot pieces made in one piece. Large recorders such as tenor, bass and large bass flutes are also built with an angled headjoint. Due to the kink, the instruments "sit" higher on the player's body and are therefore easy to play even for children or adults with short arms. Recorders usually have seven finger holes on the front and one on the back, which also functions as an overblow hole. The two lowest finger holes can be designed as double holes, which makes the relevant semitones easier to play. In the larger recorders, most of the tone holes are closed with keys because of their large gaps.