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. Changes in the position of the slider are transmitted along with "18" so that they are distinguished from changes in the value of other controllers.
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