Today the organ is still a wind instrument controlled by one or more keyboards. When a key is pressed, it opens a valve under a pipe or pipes. The wind enters the pipe, causing a tone that is constant in pitch and volume until the key is released. Both the attack and the release of the tone are controlled by the player. This is different from the piano, whose tone has a natural decay. Continuous tone is the organ's most important characteristic. (The history of the organ has always been about an ongoing attempt to control wind.)