An auxiliary (aux) send creates a copy of an audio signal and routes it to a separate bus, typically for shared effects processing. The original signal continues unaffected on its main path.
The most common use is shared reverb: Instead of inserting a reverb plugin on every track, you create one reverb on an aux bus and send varying amounts of each track to it. This is more CPU-efficient and creates a cohesive sense of space.
Pre-fader vs post-fader:
- Post-fader (default) — send level follows the channel fader
- Pre-fader — send level is independent of the fader (useful for headphone mixes)
In game audio middleware, aux sends are used for shared environmental effects — all sounds in a room might send to the same reverb bus, creating consistent spatialization.