An effects loop that routes audio from a mixer channel to an external processor and back, letting outboard gear be applied to the signal without interrupting the main path.
A send/return loop, sometimes called an effects loop or insert loop, is a pair of connections on a mixer that diverts the audio signal out to an external hardware effect processor via the send jack and then receives the processed signal back into the mixer via the return jack. The processed sound is then blended back into the channel or master bus.
Why it matters
A send/return allows a DJ to apply an outboard reverb, delay, or other processor to a signal without permanently altering the source audio or breaking the main signal chain. It also allows the wet/dry balance between processed and unprocessed sound to be controlled at the mixer rather than solely at the effects unit.
In practice
When connecting outboard gear to a send/return, match signal levels carefully: the send output is typically line level, so set the external unit's input gain to avoid clipping its input stage. If the effects unit has its own wet/dry control, set it to 100% wet so the mixer's return level knob gives you clean control over how much effect is heard.
