XLR connector

A plug and socket used in professional audio equipment, lighting controls (see DMX512) and other applications. It uses a balanced connection and locks into the socket. XLR connectors are twice the size of the standard RCA plugs and sockets found on consumer equipment.

Hot Plugging
The ground channel on the socket is designed to make contact with the ground pin on the plug before the other pins make contact. This avoids external signals and momentary distortion when cables are plugged in and out in a live session.

The XLR name comes from a particular X connector from Cannon, which was modified with a latch (the L) and a rubber compound (the R). See A/V ports and plugs & sockets.

XLR3 Connector

Although XLR connectors can have from two to six pins, this 3-pin XLR plug and socket is typically found on quality equipment for analog audio signals. Looking at the socket (left), the rightmost pin is ground; the leftmost is hot, and the bottom one is neutral.