An aux send (auxiliary send) is a channel control that copies part of a channel’s signal to an auxiliary bus while the original signal continues on its normal path to the main mix. In mixing, aux sends are used for two jobs: feeding shared effects such as reverb and delay, and building independent monitor or headphone mixes for performers.
Each channel has its own send level for each aux bus, so the engineer can decide exactly how much of every source reaches a given effect or monitor. The aux bus then sums all those contributions into one signal, which is processed or sent to an output and, for effects, returned to the mix.
How an aux send routes signal
An aux send works as a parallel tap on the channel strip. The send knob sets how much of the channel’s signal is copied, the copies from all channels are summed on the aux bus, and the bus master sets the overall level that leaves through an aux output or internal bus.
For effects, the bus output feeds a reverb, delay or other processor, and the processed signal comes back through a return channel or a dedicated effects return. The original dry signals and the returned wet signal are then blended in the main mix, which is the essence of the send and return approach.
| Element | Function | Typical control |
|---|---|---|
| Send level | Amount of one channel sent to the bus | Rotary knob or fader, often minus infinity to plus 10 dB |
| Pre or post switch | Tap point before or after the channel fader | Per send or per bus setting |
| Aux bus master | Total level of the summed bus | Fader or knob on the master section |
| Effects return | Brings the processed signal back to the mix | Return channel with fader, pan and EQ |
| Send pan | Position of the channel within a stereo aux | Linked to channel pan or independent |
On analog consoles the sends are physical knobs on every channel; in a DAW they are send slots that point to an internal bus or an auxiliary track. The logic is the same in both environments.
Pre-fader and post-fader aux sends
The tap point decides whether a send follows the channel fader. A post-fader send is taken after the fader, so pulling the fader down also lowers what the effect receives. A pre-fader send is taken before the fader, so the send level stays constant whatever happens to the main mix.
| Property | Pre-fader send | Post-fader send |
|---|---|---|
| Follows channel fader | No | Yes |
| Wet to dry ratio | Changes when the fader moves | Stays constant when the fader moves |
| Typical use | Monitor and headphone mixes | Reverb, delay and other shared effects |
| Effect of a channel mute | Depends on console design | Usually silences the send |
Choosing the wrong tap point causes classic problems. A reverb fed pre-fader keeps sounding after a vocal fader is pulled down, leaving a ghostly tail in the mix, while a monitor mix fed post-fader changes every time the front-of-house engineer rides a fader, which performers find confusing.
Aux sends compared with inserts and buses
An aux send is one of several ways to route signal to processing, and the choice depends on whether the whole signal or only a portion of it should be processed. The comparison below separates the aux send from neighboring routing concepts.
| Routing | Signal handling | Best suited to |
|---|---|---|
| Aux send | Parallel copy, original continues | Reverb, delay, parallel compression, monitor mixes |
| Insert | Entire signal passes through the processor | EQ, compressor, gate, de-esser on one channel |
| Group or subgroup bus | Channel output assigned to a bus | Controlling or processing several channels together |
| Direct out | Channel signal sent to its own output | Multitrack recording from a live console |
The practical rule is simple: time-based effects belong on sends, because one reverb shared by many channels saves processing and places all sources in one coherent acoustic space. Dynamics and EQ normally belong on inserts, because they should change the whole signal.
Setting up aux sends in a mix
A good aux setup starts with the effect set to 100 percent wet. Because the dry signal already reaches the mix through the channel, any dry signal inside the effect would double it and cause level changes or comb filtering when the send moves.
- Set the effect mix to fully wet on every send-based processor.
- Choose post-fader sends for effects so the wet balance follows mix moves.
- Choose pre-fader sends for performer monitor mixes.
- Shape the return: a high-pass filter and some low-mid cut on a reverb return keeps the mix clear.
- Name buses clearly, for example short plate, long hall and quarter-note delay.
Many engineers create a small set of shared effect buses at the start of a mix, typically one short reverb, one longer reverb and one tempo-synced delay. Sending different amounts of each instrument to these few buses gives depth and cohesion with very little processing load.
Common mistakes with aux sends
Most aux send problems come from gain structure and tap point errors rather than from the effects themselves. The following table lists symptoms that mixing engineers meet frequently.
| Symptom | Cause | Fix |
|---|---|---|
| Reverb remains after fader is down | Effect send set to pre-fader | Switch the send to post-fader |
| Sound becomes thin or phasey | Dry signal left inside the effect | Set the effect to fully wet |
| Noisy or distorted return | Send and bus levels badly staged | Keep sends near unity and adjust the bus master |
| Monitor mix jumps during the show | Monitor sends set to post-fader | Use pre-fader sends for monitors |
| Feedback in stage monitors | Too much open microphone in the aux | Reduce sends and use monitor EQ |
In DAWs, a further issue is plugin delay. Most modern hosts compensate latency on aux returns, but a processor with large lookahead on a return can still smear transients if compensation is disabled.
The idea in brief
Imagine a kitchen where every cook can pour a little of their dish into a shared sauce pot. Each cook decides how much to add, the pot is seasoned once, and then a spoonful of the sauce is served alongside every plate. An aux send is that pouring knob for each instrument in a mix.
Instead of giving every instrument its own reverb, the engineer sends a chosen amount of each one to a single reverb. The same idea is used for headphones: each musician gets their own blend without changing what the audience hears.
A practical scenario
At a small music venue, a sound engineer runs a 24-channel console for a five-piece band. Aux sends 1 to 3 are set pre-fader and feed three stage wedges, so the singer, the guitarist and the drummer each hear their own balance even when the engineer rides faders for the audience.
Aux sends 5 and 6 are post-fader and feed a plate reverb and a quarter-note delay. The engineer sends plenty of reverb from the lead vocal and snare, a little from the acoustic guitar and none from the kick and bass. When the singer moves to a ballad, a small push on the vocal send and the reverb return gives a wider, softer sound in seconds, without touching any monitor mix on stage.