MIDI Controllers
The term "MIDI controller" is used in two different ways. A MIDI controller can be defined as hardware or software that is able to transmit MIDI messages via a MIDI Out connector to other devices with MIDI In connectors. In the other, more technical sense, a MIDI controller is a parameter that can be controlled remotely through MIDI Control Change messages. For example, synthesizers commonly use controller number 74 to control a low-pass filter's frequency. If a user assigns a physical slider to transmit controller number 74, then all changes in the slider position will be transmitted as MIDI Control Change messages on controller number 74, and the synthesizer's filter frequency will change accordingly.
Read more about this topic: MIDI Usage And Applications