An Accordion is a musical instrument that belongs to the category of free reed aerophones. It consists of two wooden keyboards (for the right and left hands respectively), a bellows and various reed blocks mounted on a windchest inside. The reed blocks consist of metal tongues that vibrate to produce sound when air passes over them. By opening and closing the bellows, air is directed to the selected reed blocks. The performer uses the right hand keyboard to play the melody, while the left hand keyboard is commonly used for playing chords or accompaniment. Accordions also feature a number of buttons or levers that control various functions such as changing registers (sets of reeds) or adding effects.