The flute is a woodwind instrument, but modern flutes are made of metal. It was made of wood a long time ago. It doesn't need lip vibration like brass instruments. Flute players hold it horizontally and make a sound by blowing their breath over the edge of the hole of flute's head. This makes the air vibrate. Flutes need the second most amount of air for an instrument, next to the tuba. Flautists can change the pitch by pushing buttons or changing the direction of the breath. These buttons are called keys. The breath also can change the tone or the volume. Flute has many variations of the sound. The sound of flute is high, so composers often express it as a bird. A flute matches with many instruments such as violin and piano, and is often part of an ensemble.