MIDI

MIDI is essentially an electronic protocol for telling gear (software or hardware) what to do. The computer assigns a series of numbers from 1-127 to the different notes of the scale. This allows you to write a linear sequence of notes (often in the form of a piano or keyboard roll) in a sequencer. You can make the synthesizer or sampler play back what you want.

There are midi notes (keys or pads), and midi controllers (sliders and knobs). MIDI notes play synth notes, launch clips, and do other things that can be accomplished by a singular button press. MIDI controllers are used for things like faders, lfo speed, or filter cutoff frequency.

MIDI is a common way of sequencing songs. The composer writes midi notes in a sequence and the synth, drum machine, or sampler plays the song as composed.

It is important to distinguish between midi and audio. Midi unto itself does not make sounds, it is merely instructions for whatever it is being sent to. For example, you can feed the same midi information into different synth's and they will play the same notes with completely different sounds. This is an advantage to working with midi files because it allows more flexibility to change the tone of the melody, line, or beat as you retain the same pattern.