Keyboard Expression - Pressure Sensitivity

Pressure Sensitivity

The clavichord and some electronic keyboards also respond to the force with which a key is held down after the initial impact; they are pressure sensitive. This can be used by a skilled clavichord player to slightly correct the intonation of the notes when playing on a clavichord, and/or to play with a form of vibrato known as bebung. Unlike in a piano action, the tangent does not rebound from the string; rather, it stays in contact with the string as long as the key is held, acting as both the nut and as the initiator of sound. The volume of the note can be changed by striking harder or softer, and the pitch can also be affected by varying the force of the tangent against the string. When the key is released, the tangent loses contact with the string and the vibration of the string is silenced by strips of damping cloth.

By applying a rocking pressure up and down the key with the finger, a performer can slightly alter the vibrating length of the string itself, producing a vibrato quality known as Bebung. While the vibrato on fretless string instruments such as the violin typically oscillates in pitch both above and below the nominal note, clavichord Bebung can only produce pitches above the note. Bebung was often not explicitly indicated in sheet music; the assumption was that, like other ornaments, Bebung was to be applied at the performer's discretion. Where Bebung is indicated, it appears as a series of dots written above or below a note, with the number of dots indicating the number of movements of the finger.

On electronic keyboards and synthesizers, pressure sensitivity is sometimes called aftertouch. The aftertouch sensors detect whether the musician is continuing to exert pressure after the initial strike of the key. The aftertouch feature allows keyboard players to change the tone or sound of a note after it is struck, the way that singers, wind players, or bowed instrument players can do. On some keyboards, sounds or synth voices have a preset pressure sensitivity effect, such as a swell in volume (mimicking a popular idiomatic style of vocal performance with melodies) or the addition of vibrato. On some keyboards, the player can select which effects are applied when aftertouch is detected. This allows a performer to custom-tailor the effect that they desire. It may also facilitate the imitation of various non-keyboard instruments. For example, a keyboardist who wishes to imitate the sound of a heavy metal guitar solo could use a distortion guitar sound, and then set the aftertouch feature to apply a pitch bend to the note.