鍵盤表情
维基百科，自由的百科全书
通常以expression(表情)簡短表示鍵盤表情，代表鍵盤樂器對鍵盤回應音樂動態的能力。
例如：鋼琴可以顯著地反應出琴鍵一開始被壓下時的力量，這就是力度感應。一些早期鍵盤，例如大鍵琴，相對於鋼琴少了力度感應，這個關鍵是鋼琴的優點。
大鍵琴和一些電鋼琴同樣對鍵盤被壓下後持續不放的力量感應，稱為壓力感應。這項功能可以被超級大鍵琴手彈出輕微修正的音調，或/及 彈出一種稱為顫抖(bebung)的抖音表現。
有些人把力度感應當成同義字，而和壓力感應一詞有點混淆，為了避免這種混淆情況，某些時候會把壓力感應稱為後壓(aftertouch)。
不論力度和(真實)壓力感應，由MIDI規範分別單獨支援。
通常只有高階電鋼琴使真實的壓力感應生效，直到最近大部分(非全部)的電鋼琴也開始支援力度感應。部分劣等鍵盤是純粹力度感應的樂器，卻號稱為壓力感應，這導致生產商走向一種不幸的趨勢。
第三種感應轉移感應，這種轉移現象常見於風琴。大部分機械式風琴和部分的電子式風琴都是轉移感應，換言之，你可以把琴鍵分次按下，在風琴裡相對應的音(管風琴，腳踏式風琴，或相似)比完全按下的時候會產生一些少量的聲音。小型桌上風琴和手風琴對於琴鍵被按下時會增加聲音的輸出是很類似。在手風琴或少數的風琴，甚至可以發現小小的循環伴奏(單鍵和絃)鍵，因此，電子式風琴保留這項鍵盤表情：
A 34-rank organ located in the Swiss village of Ursy is equipped with hi-tech features from Syncordia including 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. http://www.ohscatalog.org/worlarorolun.html Other more sophisticated forms of sensitivity are common in organ keyboards. For example, 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. It should be noted that, 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.
