/ɔːks sɛnd/
Aux Send is a channel-level knob or fader that taps a copy of the channel's audio and routes it to a shared auxiliary bus, enabling parallel effects, monitor mixes, and group processing without altering the dry signal path.
Every great reverb tail, every pumping parallel compressor, every perfectly tailored headphone mix owes its existence to one deceptively simple concept — the ability to send a copy of your signal somewhere else entirely, without touching the original.
An aux send — short for auxiliary send — is a channel-level control on a mixing console or DAW channel strip that taps a copy of the audio signal and routes it to a shared auxiliary bus. The crucial distinction is that the send is a parallel path: the original signal continues unaltered down the channel's main fader and into the mix bus, while the send feeds a separate destination independently. The amount of signal dispatched to that destination is governed by the send level control, typically calibrated in dB, ranging from negative infinity (fully off) up to unity gain (0 dB) or sometimes beyond, depending on the console or software implementation.
The term encompasses both the physical or virtual control itself and the conceptual act of routing. On an analog console — say an SSL 4000 or a Neve 8078 — an aux send appears as a rotary knob on each channel strip, feeding a summing bus shared by every channel in the desk. In DAWs such as Ableton Live, Logic Pro, or Pro Tools, the equivalent is a send slot in the channel strip that routes to a return track, aux track, or bus, with a level control expressed as a fader or rotary. The destination — typically called a return, aux return, or effects return — hosts the processing that acts on the combined, blended signal arriving from all contributing sends.
Aux sends operate in one of two fundamental modes: pre-fader and post-fader. A post-fader send taps the signal after the channel fader, meaning the send level is proportionally influenced by the fader position. Raise the channel fader and more signal flows to the aux bus; pull it down and the send diminishes correspondingly. This behavior makes post-fader sends ideal for shared effects like reverb and delay, since the wet-to-dry relationship remains perceptually consistent as you automate levels. A pre-fader send taps the signal upstream of the channel fader, making it completely independent of the fader's position. Pulling a channel to silence does not affect its pre-fader send contribution — a critical property for creating independent monitor or headphone mixes for performers.
The power of aux sends lies in their economy and flexibility. Rather than placing a reverb plugin on every individual vocal track, a single high-quality reverb instance lives on the return channel, and every vocal sends a proportionally scaled copy of itself to that shared space. CPU load is dramatically reduced, phase relationships between sources sharing the same reverb room are preserved, and the reverb's character — its pre-delay, decay, modulation — remains cohesive across the entire mix. This shared-bus paradigm is the conceptual backbone of professional mixing, used universally from tracking sessions through final mixdown and mastering preparation.
At the hardware level, an aux send is implemented as a voltage-controlled tap point in the channel's signal path. On an analog console, each channel's audio passes through a series of amplifier stages, and the aux send knob controls an attenuator that extracts a proportional copy of the post-EQ (or pre-EQ, depending on the console's topology) signal. This tapped signal is then summed on the aux bus — a dedicated wire running the length of the console — with the tapped signals from every other channel. The bus feeds the input of a bus amplifier, whose output goes to the effects unit or monitor amplifier, and the processed signal returns through the console's aux return inputs, appearing on the stereo mix bus at a level controlled by the return fader.
In a DAW environment, the same topology is implemented in the digital domain through the software mixer's routing matrix. A send slot on a channel strip creates an internal signal branch; the send's level parameter scales the gain of that branch before it is mixed into the designated bus or return channel. Crucially, the DAW maintains sample-accurate alignment between the dry channel signal and any processed signal coming back from a return channel, provided there is no external hardware insert or plugin-induced latency on the return path that exceeds the DAW's delay compensation window. Modern DAWs implement automatic delay compensation (ADC) to align all paths, but latency introduced by certain plugins — convolution reverbs with long impulse responses, for example — can push latency beyond what ADC can transparently handle, making plugin latency awareness essential in complex send configurations.
Pre-fader versus post-fader routing is determined by where in the signal chain the tap point sits. Post-fader taps follow the fader gain stage, so the mathematical relationship is: Send Level (dB) = Channel Fader Level (dB) + Send Knob Attenuation (dB). Pre-fader taps bypass the fader entirely, reading from the pre-fader signal node, making the send level solely a function of the send knob and independent of the fader's position. Some consoles and DAWs also offer pre-EQ send options, allowing the raw, unprocessed signal to be sent — useful for parallel processing chains where you want the send to reflect the dry captured signal rather than the EQ'd version headed to the mix bus.
When multiple channels send to the same aux bus at different levels, the bus summing amplifier (analog) or the internal summing engine (digital) combines all contributing signals. The return channel then applies processing to this summed signal. This shared-resource model means that the reverb tail on a snare and the reverb tail on a lead vocal exist in the same acoustic space as defined by a single reverb plugin — they interact within the reverb's algorithm as if they were played in the same room. This coherence is one of the principal aesthetic reasons to use sends rather than duplicating the same effect on individual channels.
Understanding gain staging within the aux send chain is essential for professional results. If sends from twenty channels all arrive at unity gain at the return channel's input, the summed level can easily clip the return channel's input stage or cause the reverb plugin to receive a dangerously hot signal. Best practice is to set individual send levels conservatively — often between −12 dB and −6 dB — so that the summed bus level presents a healthy input level to the effect, and the return channel's fader provides final level trimming before the processed signal enters the mix bus.
Diagram — Aux Send: Signal flow diagram showing pre-fader and post-fader aux send routing from three channels to a shared reverb return bus.
Every aux send — hardware or plugin — operates on the same core parameters. Know these and you can work with any implementation.
The primary send control, calibrated in dB, determines how much of the channel's signal is copied to the destination bus. In practice, most engineers set reverb sends between −18 dB and −10 dB, achieving a subtle wet contribution without overwhelming the dry signal. Pushing the send level to 0 dB or above can flood the return with signal, causing the reverb or effect to smear and lose definition.
This mode switch defines whether the send taps the signal before or after the channel fader gain stage. Post-fader (default for effects sends) maintains a consistent wet-dry ratio as the fader moves; pre-fader (used for monitor mixes and parallel processing) makes the send independent of the fader. On analog consoles this is a dedicated button per channel; in most DAWs it is accessible by right-clicking the send slot.
Available on some consoles and DAWs, this determines whether the channel EQ is included in the send signal. Post-EQ sends are most common, ensuring that the tonal shaping applied to the channel is reflected in the auxiliary signal — for instance, high-pass filtering a room mic before sending it to a reverb bus. Pre-EQ sends give the aux bus the raw, uncolored signal, useful for parallel saturation or compression chains where you want the effect to process the full-bandwidth original.
Many professional consoles and DAWs allow the send signal to be panned independently before it reaches the aux bus. This is particularly useful on consoles with stereo aux buses, allowing a snare or guitar to be positioned within the stereo field of a shared reverb bus. In DAWs, the send panning is separate from the channel's main pan, giving fine control over how the source contributes to the stereo image of the effect return.
The return fader sits on the aux return (or return track) channel and determines how much of the processed signal enters the main mix bus. It is the global wet-amount control for the entire shared effect, affecting all channels simultaneously. Automating the return fader is the cleanest way to ride the overall reverb depth across a song's sections — bringing it up in sparse verses and pulling it back in dense choruses — without disturbing individual send levels.
Most consoles and DAWs provide a per-send mute or enable toggle, allowing a single channel to be removed from an aux bus without adjusting its level. This is invaluable during sessions where a performer wants to be removed from a specific headphone mix without disrupting the overall balance, or during mixing when you want to A/B a channel's contribution to a reverb bus. In Pro Tools, this is accessible directly on the send assignment; in Ableton, toggling the send activator button achieves the same result.
Session-ready starting points. These are starting-point values based on common professional practice; adjust by ear relative to your session's loudness and the effect's character.
| Parameter | General | Drums | Vocals | Bass / Keys | Bus / Master |
|---|---|---|---|---|---|
| Send Level (Reverb) | −15 to −10 dB | −18 to −12 dB (snare) | −14 to −8 dB | −20 to −16 dB | −12 to −6 dB |
| Send Level (Delay) | −18 to −12 dB | −24 to −18 dB | −16 to −10 dB | −22 to −16 dB | −14 to −8 dB |
| Pre/Post Mode | Post-fader | Post-fader | Post-fader | Post-fader | Pre-fader (monitor) |
| Send Count per Channel | 1–2 typical | 2–4 (verb, room, parallel) | 2–3 (verb, delay, harmony) | 1–2 | 1 (monitor) |
| Return Fader (Reverb Bus) | −6 to 0 dB | −6 to −3 dB | −4 to 0 dB | −10 to −6 dB | −6 to 0 dB |
| Parallel Comp Send Level | 0 dB (unity) | 0 dB (unity) | −3 to 0 dB | 0 dB (unity) | 0 dB (unity) |
| Monitor Mix Send Level | Per performer need | 0 dB (self) | 0 dB (self), −6 dB (band) | −6 to 0 dB | N/A |
These are starting-point values based on common professional practice; adjust by ear relative to your session's loudness and the effect's character.
The concept of an auxiliary send arose from the practical demands of large-format broadcast and recording consoles in the late 1950s and early 1960s. Early console designs by manufacturers such as Langevin and Neve in the UK, and by Bill Putnam Sr.'s Universal Audio in the United States, incorporated additional output busses on channel strips to feed echo chambers, tape delays, and monitor amplifiers. Putnam, working at Universal Recording in Chicago and later at United Recording in Los Angeles, is widely credited as one of the first engineers to standardize the parallel-effects-send workflow, using physical echo chambers fed by auxiliary outputs on his custom consoles to create the reverb heard on records by Nat King Cole and Muddy Waters in the late 1950s.
The 1960s and early 1970s saw the aux send formalized into a standard feature of professional console design. EMI's custom TG12345 console installed at Abbey Road Studios in 1968 provided multiple auxiliary send buses per channel, enabling The Beatles and their engineers — particularly Geoff Emerick — to exploit complex parallel effects chains, including the ADT (Automatic Double Tracking) effect and tape-fed echo sends, with a degree of flexibility unprecedented at the time. The Neve 8078 and later the SSL 4000 Series — introduced in 1976 and 1979 respectively — refined the aux send to its now-iconic form: four to eight per-channel send knobs feeding independently addressable mix buses, establishing the template that all subsequent console and DAW designs have followed.
The studio monitor mix application of aux sends became equally important during the multitrack recording era of the 1970s. As session counts grew to 24 and then 48 tracks, headphone monitor mixes for performers became a logistical necessity. Pre-fader sends allowed engineers to construct entirely custom mixes for each performer — more click, less reverb, louder bass — independent of the main control room mix. Consoles like the MCI JH-500 series and the SSL 4000 made this workflow practical at large scale, with some desks offering dedicated, separately addressable monitor send buses labeled simply AUX 1 through AUX 8.
The arrival of DAWs in the 1990s translated the aux send paradigm into software without conceptual alteration. Digidesign's Pro Tools introduced aux input tracks and bus routing in its early TDM versions of the mid-1990s, allowing engineers to replicate console-style send/return workflows within the digital environment. Steinberg's Cubase and later Logic Audio (before Apple's acquisition) implemented send slots on channel strips in the same period. The fundamental behavior — send level, pre/post switch, bus assignment, return channel — has remained essentially unchanged since, a testament to how completely the original analog architecture solved the routing problem. Today the aux send is one of the most universally consistent features across all DAW platforms, its interface variations cosmetic rather than functional.
For drums, the aux send is the engine of the parallel compression technique that defines modern trap, hip-hop, and rock productions. A dedicated parallel compression bus receives post-fader sends from kick, snare, and overhead channels at or near unity gain. A heavily limiting compressor — often a hardware-modeled plugin such as the UAD API 2500, Waves SSL G-Bus, or even a slammed 1176 — crushes the parallel signal into a dense, pumping mass. The return fader blends this crushed signal back beneath the dry, transient-rich drum mix, adding sustain and density without sacrificing the initial attack. Send level to this bus is typically at 0 dB or near unity, since you want the compressor to see the full drum signal; the blend is managed entirely by the return fader.
For vocals, aux sends serve two distinct roles: shared reverb and delay for depth and space, and parallel saturation or harmonic enhancement for presence. A plate reverb return — loaded with Valhalla Plate, UAD EMT 140, or a similar plugin — receives sends from lead vocal and background vocal channels at individually calibrated levels, typically −14 dB to −8 dB depending on desired wetness. The same vocal channels often send to a separate tempo-synchronized delay bus (eighth-note or dotted-eighth delays are common in pop and R&B), allowing independent control of reverb depth versus echo prominence. A third send to a saturation bus — routed through a subtle tape saturation plugin — can add harmonic density without the producer touching the vocal's EQ or compression chain.
In electronic music production, aux sends underpin the creation of sidechain-triggered effects and send-based automation that defines genres like techno, house, and ambient. A send from a kick drum to a sidechain input on a reverb or filter bus allows the effect to be rhythmically gated or modulated — a technique audible on countless records from producers like Burial, Four Tet, and Aphex Twin. Producers also exploit automation of send levels over time, gradually opening a reverb send across a build section to increase perceived space and tension, then cutting it sharply on the drop for contrast — a structural device as important as arrangement changes.
In tracking and live recording contexts, pre-fader aux sends are indispensable for constructing performers' headphone mixes. A session drummer, vocalist, and bassist each receive a separate pre-fader send mix routed to their respective in-ear monitor or headphone amplifier. The engineer can adjust the main mix freely — muting, soloing, adjusting levels — without disrupting what any performer hears. This separation of concerns between the control room mix and the performer mixes is one of the most practically important applications of the pre-fader send mode, and one that new engineers often underestimate until they first cause a performer to lose their headphone mix by inadvertently muting a channel that was the sole source of click track in their ears.
One email a week. The techniques behind the terms — curated by working producers, not algorithms.
Abstract knowledge becomes practical when you can hear it in music you know. These tracks demonstrate aux send used intentionally, at specific moments, for specific purposes.
The gated reverb snare that defines this track is a direct product of aux send routing. Hugh Padgham, working at the Townhouse Studios on the SSL 4000 console, sent the snare signal to a reverb bus and then placed a noise gate on the return channel, triggering the gate's close point to create the abrupt, truncated reverb decay. The send level was set high enough that the reverb tail would sustain audibly before the gate cut it, and the gate threshold was calibrated so that bleed from other instruments would not trigger false openings. Listen from the downbeat: the dry snare hits first, and the cavernous gated reverb blooms a few milliseconds behind, then snaps shut — a textbook pre/post dynamics chain on an aux return.
Nigel Godrich's work on Kid A and this track in particular demonstrates restrained, long-decay plate reverb sends applied with precision to the string and vocal layers. The orchestral strings appear to exist in a vast, undifferentiated space — achieved by sending multiple string mic channels to a shared plate reverb bus at low send levels (perceptibly −12 dB or below) with a decay time in excess of four seconds. The result is that the strings seem to dissolve rather than stop. Notice how Thom Yorke's vocal has a distinctly shorter, closer reverb — likely a separate send bus with a shorter decay — preserving intelligibility against the expansive string wash.
Mike Will Made-It's production uses aggressive parallel compression on the drum bus, a technique visible in the way the 808 kick and snare sustain and bloom rather than simply decay. The kick's sub content appears to be sent at near-unity to a heavily compressed parallel bus, adding density and sustain that sits underneath the transient-led dry signal. At 0:33, when the drums enter fully, listen to the low-end weight and the way the snare seems to push forward without losing its initial crack — a hallmark of well-blended parallel send compression.
This Apollo: Atmospheres & Soundtracks track exemplifies the use of aux sends for ambient texture building, predating the digital era. Eno used Lexicon reverb units fed by aux sends from synthesizer and guitar channels, with very long decay times (8–12 seconds) and high send levels that sometimes exceeded the dry signal in level. The result is a mix where the wet and dry signals are nearly equal contributors, creating a diffuse, floating sound world. The technique of deliberately over-sending to long-decay reverbs — letting the return dominate — is foundational to ambient and atmospheric mixing.
The most common aux send type, tapping the signal after the channel fader to maintain a proportional wet-dry relationship as fader levels change. Used universally for shared reverb and delay buses, this mode ensures that as a channel is automated up or down in the mix, its contribution to the effects bus scales accordingly. On most consoles and DAWs, post-fader is the default send mode.
A pre-fader send provides a tap point entirely independent of the channel fader, making it the standard choice for constructing performers' headphone or in-ear monitor mixes during tracking. The engineer can pull a channel completely out of the main mix without affecting the performer's headphone blend, and vice versa. This mode is also used for parallel processing chains where fader independence is desirable.
A dedicated use of aux sends — typically post-fader at or near unity gain — to route a copy of a channel or group to a heavily processed bus (often parallel compression or distortion) whose output is blended back into the mix via the return fader. The defining characteristic is that the dry signal remains untouched on the main channel while the return adds density, saturation, or dynamic control. This is the conceptual basis of New York-style parallel drum compression.
A specialized pre-fader send application where multiple independent auxiliary buses (Cue 1, Cue 2, Cue 3 etc.) each feed a separate headphone amplifier output for a different performer in the recording space. Modern dedicated headphone mix systems such as the Aviom A-16 or Hear Technologies Hear Back operate on this principle, receiving pre-fader aux sends from the console and distributing them to personal mixing stations. Each performer controls their own blend without engineer intervention.
Rather than routing to a traditional effects or monitor bus, a sidechain send routes a channel's signal (or a filtered version of it) to the sidechain input of a compressor, gate, or dynamic effect on another channel. This is the mechanism behind kick-to-compressor sidechaining for pumping house music and behind drum-triggered noise gates on recorded performances. The send level controls how strongly the sidechain input is driven, affecting the trigger threshold and detection sensitivity of the dynamic processor.
These MPW articles put aux send into practice — specific techniques, real tools, and applied workflows.