Keyboard Expression - Displacement Sensitivity

Displacement Sensitivity

A third form of sensitivity is displacement sensitivity. Displacement sensitive keyboards are often found on organs. Most mechanical organs, and some electrically actuated organs, are displacement sensitive, i.e. when a key is pressed partway down, the corresponding note (pipe, reed, or the like) in the organ will produce a different, quieter sound than when the key is fully depressed. In some organs, the pitch and/or tone colour may also be altered. Small tabletop organs and accordions often respond similarly, with sound output increasing as keys are pressed further down. Even the small circular accompaniment ("one button chord") keys found on accordions and on some organs exhibit this phenomenon. Accordingly, some electrically actuated organs have retained this form of keyboard expression:

A 34-rank organ located in the Swiss village of Ursy is equipped with hi-tech features from Syncordia including what has been erroneously claimed to be the first non-mechanical action in history to directly control the opening of a pipe organs pallets in direct proportion to the movement of the keys, thus ostensibly combining the virtues of electric action with the intimate control of tracker action. However, Vincent Willis' 1884 patent Floating Lever pneumatic action also had this capability.

Other more sophisticated forms of sensitivity are common in organ keyboards. Both the Pratt Reed and Kimber Allen 61-key (5-octave) keyboards have provision for installing up to nine rails, so that they can sense various amounts of displacement, as well as velocity in various regimes of distance from the top to the bottom of the key travel of each key. Some modern instruments such as the Continuum, a MIDI controller for keyboards, have extremely sophisticated human interface schemes, allowing dynamic control in three dimensions. In principle, displacement can be differentiated to get velocity, but the converse is not entirely practical, without some amount of baseline drift. Thus a displacement sensing keyboard may have greater versatility when it is desired to have both organ and piano behaviour in an input device.