Auxiliary sends: pre-fader and post-fader uses

Console auxiliary sends provide a second route for a channel signal, usually feeding an effects processor, a parallel recording chain or a monitor mix. The channel controls how much signal enters that route, while the destination determines what happens next. On an analogue desk this may be a summing amplifier and a patchbay; in a DAW it is a software bus and plug-in. The underlying principle remains the same even when the implementation changes.

The key routing decision is where the send is tapped. A pre-fader send sits ahead of the channel level control, so moving that fader does not alter the feed. A post-fader send follows the fader and therefore tracks it. Neither name guarantees a fixed signal order: trim, equalisation, dynamics, pan, mute and solo can sit on either side of the tap, depending on the console.

Australian studios span large-format SSL and Neve rooms in Sydney and Melbourne, as well as project and broadcast facilities in Brisbane, Adelaide and Perth. The local second-hand market is active, with vintage desks arriving through dealers, auction sales and private imports from the United Kingdom, the United States and Japan. Australian engineers also use familiar studio shorthand: a reverb return is commonly called “the verb”, and a musician monitor mix is often called “foldback”. These habits sit alongside the technical language of pre-fader and post-fader routing.

Why aux routing matters

An aux send differs from an ordinary channel output because the source signal is divided rather than simply routed onward. The send control acts as an attenuator feeding a shared bus, so several channels can contribute to one processor or bus. This makes auxiliary buses useful for parallel compression, reverbs, delays, foldback monitoring paths and feeds to a remote recorder. The receiving bus may return to the main mix or feed an entirely separate destination.

Console terminology is inconsistent. “Aux” may name an effects send, a monitor feed, an effects return or any auxiliary input or output, so the label alone does not describe the signal path. On an SSL or AMS/Neve desk, a channel strip can place the tap after EQ and compression, while another section may offer a choice of pre- or post-fader sources. Consult the block diagram rather than assuming every send follows the same rule. The exact position of pan, mute and solo also determines whether those controls affect a send.

Pre-fader applications

Pre-fader routing gives the engineer a signal reference that remains stable when the channel fader is moved, making it valuable for external dynamics, recording feeds and foldback. A parallel compressor can be set to catch peaks without being dragged up and down by the mix balance. A pre-fader monitor tap can also keep a performer’s headphone mix steady while the engineer changes the vocal level in the front-of-house mix.

The practical distinction is clearest when a fader moves. The console’s motorised Yamaha PM4000 uses motorised controls for repeatable recall, yet a pre-fader feed can remain independent of the channel fader while its post-fader counterpart changes. Motorised recall does not alter this principle; it simply makes the contrast between two routing choices easier to hear during a comparison.

Pre-fader does not mean untouched. Channel trim, EQ and dynamics processors may precede the send tap, while pan, mute and solo may sit after it. If a compressor is already in the channel strip, the external unit receives that processed signal rather than a pristine source. Check polarity, phase alignment and the order of every stage. For multitrack recording, metering at both the source and send ensures the incoming level stays usable without riding the channel fader.

Post-fader applications

Post-fader routing follows the level presented to the mix, so it is the usual choice for a conventional effects send. Raising a vocal fader adds more signal to the plate reverb, and lowering it reduces the wet contribution while the dry vocal remains in the channel path. This relationship makes post-fader sends responsive to arrangement, performance and fader automation. It also means an effect can disappear as a source is deliberately pulled down.

The placement of pan and mute remains crucial. On some desks the post-fader tap follows the pan pot, making a stereo send move with the channel image; on others the feed is tapped before pan. Mute behaviour can also vary if the send is derived upstream of the channel mute. A useful hybrid arrangement places a vocal on a post-fader plate return and a separate pre-fader feed into a compressor or alternate ambience. The two paths can then be balanced independently.

Practical routing choices

Suitable pre-fader assignments include:

Common post-fader assignments include:

Choosing between these options starts with the musical job. Decide whether the send should represent the source, the channel as heard in the mix, or an entirely separate feed. Verify the choice by pulling the fader, moving the pan, engaging mute and solo, then listening at both the bus and the processor. Check the return as well: a send can be correct while the return level, polarity or routing defeats its purpose.

Channel strips, taps and console differences

Console designs do not use “aux” consistently, and the differences matter more than the label. An SSL channel may feed its send from a point after EQ and compression, while an AMS/Neve section can expose a separate pre-fader pickup. A general signal-flow reference can help with tracing block diagrams, but the console’s own manual remains the authority for gain, switching and pad order. Look for whether trim precedes the send, whether the send pot remains active with other functions engaged, and whether a pad changes the bus level as well as the channel.

The effects return is the other half of the arrangement. It may enter the mix through a dedicated return fader, land directly on the stereo bus or feed a separate monitor selector. On a larger analogue desk, aux numbering and pairing can determine whether several sends feed one effects unit or whether paired channels control separate inputs. Restore the original balance by returning dry and wet paths to equivalent listening levels, then null or bypass the processor to expose phase or noise problems.

Automation, monitoring and DAW workflows

Automation changes the usefulness of each tap. A post-fader effect send follows a fader move or written automation, allowing a vocal to open into more plate as the phrase builds. A pre-fader send remains steadier under those moves, which is useful for an external compressor or a recorder that must not inherit the mix engineer’s decisions. Remember that mute, solo and busing may still alter a nominally pre-fader feed.

Modern DAW workflows blur the hardware distinction without removing it. A software track output usually represents post-fader level, while a selectable software send may be switched before or after the channel fader. An external processor connected through an interface adds converter delay, clock alignment and possible loop latency to the routing. Keep the hardware return path stable, set the DAW and interface sample rates together and compensate for any round-trip delay before judging the effect in context.

Physical fader travel affects how easily post-fader changes can be performed and read. The practical comparison of fader length differences explains how a longer throw can make fine adjustments easier to judge, especially when motor recall is involved. A compact 60 mm throw may cover its useful range more quickly, while a 100 mm fader offers finer hand control across a wider area. Digital resolution, motor mechanics and the fader law determine the real advantage.

Put auxiliary sends to work

A disciplined session starts with a routing sheet, not with a patched send found by trial and error. Label the source, send position, destination, processor or bus, return path and automation owner. Audition each feed in context, then document any channel-strip controls that affect it. That record prevents a recalled setting or a visiting engineer from turning a stable pre-fader feed into something quite different.

Use pre-fader routing for predictable parallel processing, recording and monitor references; use post-fader routing when effect balance should follow the channel in the mix. Test both choices before committing, keep gain staging honest and mark every tap in the desk documentation. Take that routing decision before the next session and label every aux.