The sound from an organ comes from of a set of pipes of different lengths, through which air is blown. The instrument is controlled by a keyboard resembling a piano keyboard. Large organs usually have two keyboards and a set of foot pedals arranged in the same manner as the piano keys. Traditional church organs used mechanical bellows to generate the wind, but modern ones use electric fans.
Organ keyboards are called manuals, and the foot pedals are called the pedal-board. Traditional organs also have a set of stops, which are knobs connected via levers to sliders which open or close ranks (or groups) of pipes. In this way, depressing a single key on one manual may sound several pipes simultaneously. Different stops open different combinations of pipes, creating differing sound qualities or timbres.
Since the invention of the electronic oscillator, modern electric organs have been developed which simulate the sounds of traditional pipe organs quite successfully. Even more realistic today are the sampled organ sounds used by modern digital keyboards and digital synthesizers.