page_title: Keyboard expression
section_title: Pressure sensitivity or aftertouch
hierarchical_section_title: Keyboard expression / Pressure sensitivity or aftertouch
caption_attribution_description: English: Synthesizers Português: Sinterizador Yamaha
context_page_description: Keyboard expression is the ability of a keyboard musical instrument to change tone or other qualities of the sound in response to velocity, pressure or other variations in how the performer depresses the keys of the musical keyboard. Expression types include:
  Velocity sensitivity—how fast or hard the keys are pressed
  Aftertouch, or pressure sensitivity — the amount of pressure on a key, once already held down
  Displacement sensitivity—distance that a key is pressed down
  Keyboard instruments offer a range of expression types. Acoustic pianos, such as upright and grand pianos, are velocity-sensitive—the faster the key strike, the harder the hammer hits the strings. Baroque-style clavichords and professional synthesizers are aftertouch-sensitive—applied force on the key after the initial strike produces effects such as vibrato or swells in volume. Tracker pipe organs and electronic organs are displacement-sensitive—partly depressing a key produces a quieter tone.
context_section_description: The clavichord and some electronic keyboards also respond to the amount of force applied after 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 root note, clavichord bebung only produces pitches above the note.
  Sheet music does not often explicitly indicate bebung. Composers generally let players apply bebung at their discretion. When sheet music does indicate bebung, it appears as a series of dots above or below a note; the number of dots indicates the number of finger movements.
  On electronic keyboards and synthesizers, pressure sensitivity is usually called aftertouch. The vast majority of such instruments use only channel aftertouch: that is, one level of pressure is reported across the entire keyboard, which affects either all notes pressed (even ones not being pushed into aftertouch) or a subset of the active notes in some instruments that allow this level of control. A minority of instruments have polyphonic aftertouch, in which each individual note has its own sensor for pressure that enables differing usage of aftertouch for different notes. 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 - a good example of such an instrument being Yamaha's richly-programmable cult-status synthesiser-workstation, the Yamaha EX5 - the player can select the effects to which aftertouch applies. 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.
caption: A 2000s-era digital keyboard
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