MIDI is a protocol used to transmit data about musical events.
A MIDI connector uses three pins: ground, +5V, and a data sink. It can be used over five-pin DIN, TRS, TS, or purely digitally. Although not standardised for a long while, manufacturers have used MIDI over TRS (most commonly 3.5mm) for a long time. There are three TRS variants.
|Pin function||DIN connector pin1||TRS A (standard)||TRS B||TS / TRS C|
|Data (current sink)||5||Tip||Ring||Tip|
|+5V (current source)||4||Ring||Tip||Sleeve|
DIN connector does not use pin 1 or 5. Whack! ↩