A typical MIDI setup might consist of a digital piano keyboard which can send messages relaying information such as pitch, velocity (how loudly or softly a note is played), vibrato, volume, panning, modulation, and more to a sound synthesizer which converts that into audible sound. The keyboard could also send its signals to desktop music scoring software or a digital audio workstation (DAW) which could then convert the signals into written notation, save them as a sound file, and more.
MIDI is a fairly versatile protocol, too. In addition to playing and recording music, it has become a standard protocol in stage and theater applications, as well, where it is often used to relay cue information or control lighting equipment.
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