A musical keyboar is the set of adjacent depressible levers or keys on a musical instrument, particularly the piano. Keyboards typically contain keys for playing the twelve notes of the Western musical scale, with a combination of larger, longer keys and smaller, shorter keys that repeats at the interval of an octave. Depressing a key on the keyboard causes the instrument to produce sounds, either by mechanically striking a string or tine (piano,electric piano); plucking a string (harpsichord, clavichord); causing air to flow through a pipe ( organ); or strike a bell ( carillon). On electric and electronic keyboards, depressing a key connects a circuit ( Hammond organ, digital piano, synthesizer). Since the most commonly encountered keyboard instrument is the piano, the keyboard layout is often referred to as the "piano keyboard."