MIDI controller

MIDI controller is used in two senses. In one sense, a controller is hardware or software which generates and transmits MIDI data to MIDI-enabled devices. In the other more technical sense, a MIDI controller is an abstraction of the hardware used to control a performance, but which is not directly related to note-on/note-off events. A slider assigned to open and close a low-pass filter on a synthesizer may be assigned to controller 18, for example.