The two main audio connectors in DJ rigs: RCA (unbalanced, consumer) and XLR (balanced, professional, used for long runs and PA connections).
RCA connectors carry an unbalanced signal and are standard on home audio gear, most DJ controllers, and turntable outputs. XLR connectors carry a balanced signal that rejects interference over long cable runs, making them the standard for club and live PA connections.
Why it matters
Matching the right connector type to the destination prevents signal loss, noise, and level mismatches. Using an unbalanced RCA cable to run 20 meters to a PA will introduce noise that an XLR cable with the same run would reject entirely.
In practice
Use XLR from the mixer master output to any powered speaker or amplifier whenever cable runs exceed a few metres. Use RCA only for short connections between gear on the same table, such as turntable to mixer or controller to an interface.

