Musical Instrument Digital Interface (MIDI) is an industry standard protocol that instruments and computers use to communicate musical ideas with each other. The origins of MIDI started with a 1981 paper titled Universal Synthesizer Interface by Dave Smith and Chet Wood. There’s a wide world of exploration possible inside the MIDI protocol, but for the scope of this course we’ll limit our discussion to the basics of how it works.
Since MIDI works with computers and other digital interfaces it’s necessary to describe music a little differently. Instead of the scientific note descriptions like “A4” or “C6,” MIDI uses the numbers 0-127 to describe the notes. “C4” (aka middle C on the piano) is given the value of 60. Each note has its own number; a “C#4” is 61, a “C3” is 48, etc. Below is a handy graphic that maps all of the MIDI note values to keys on a piano.
Each MIDI note value is also paired with a velocity value ranging from 0-127. These values are the MIDI equivalent to dynamics. Another handy chart is included below to give you a rough approximation of how to map dynamics to MIDI velocity values.
MIDI is a time based protocol, meaning that all of the events are assigned a specific time to start and stop based on the MIDI timeclock. This may sound confusing at first, so let’s consider the MIDI timeclock as a score. Each part on the score gives the conductor and musicians information on when to play, what notes to play, and how loud to play them.
All MIDI notes need a note on and note off message to be complete! Without a note off message the note will be performed forever (or at least until you unplug your machine). Fortunately, most MIDI software and hardware are created to always include note off messages.