What is MIDI Aftertouch?

MIDI Aftertouch is a type of MIDI control message that is sent after a key on a MIDI controller is pressed and held down. It measures how much additional pressure is applied to the key and allows performers to control sound parameters in real time without releasing the note.

When a musician presses a key on a MIDI keyboard and continues to apply pressure, the controller can transmit aftertouch data. This information can be used to modify aspects of the sound such as vibrato, filter cutoff, volume, or modulation, depending on how the instrument or software is programmed.

There are two main types of aftertouch: channel aftertouch and polyphonic aftertouch. Channel aftertouch applies the same pressure value to all notes being played on a MIDI channel, while polyphonic aftertouch sends separate pressure data for each individual key, allowing more detailed expressive control.

MIDI aftertouch is supported by many synthesizers and virtual instruments inside digital audio workstations such as Ableton Live, FL Studio, and Logic Pro. When used effectively, it allows performers to add expressive changes to sounds during a performance without needing additional knobs or controllers.