XLR Audio Pinout
3-pin male connector, looking at the pins with the latch at the top. Check your board against its silkscreen before wiring power.
Balanced audio in one paragraph
Pins 2 and 3 carry the same signal with opposite polarity. The receiving end subtracts one from the other, doubling the wanted signal and cancelling the hum both wires picked up along the way. Pin 1 is the shield, bonded to the connector shell.
Pin 2 hot, always
AES14 fixes pin 2 as the positive leg and every piece of modern gear follows it. When soldering cables, run the shield to pin 1 at both ends. If you meet a ground loop, fix it with a proper ground-lift box, never by cutting pin 1 inside a cable where the next person will never find it.
Male and female are mirrors
This diagram shows a male connector from the front. On a female connector the same pin numbers appear mirrored left to right, which is exactly what makes a cable end-to-end straight through.
Sources and datasheets
This diagram was cross-checked against the manufacturer documentation below plus at least two independent references before publishing. When they disagreed, the manufacturer won.
More boards and plugs live on the pinouts index.