Aux, Group and Matrix: What the Sends on a Mixer Are Actually For

In this guide:Aux sends · Groups · Matrix · Bus count · Picks · FAQ

People buy mixers by channel count, then discover the limit is somewhere else entirely. A desk with 32 inputs and four aux sends cannot feed six monitor mixes, no matter how many channels are free.

Auxes, groups and matrix outputs are the three ways audio leaves a desk other than through the main mix. Knowing which is which is what lets you specify a desk properly.

Aux: a separate mix of the same channels

An aux send builds a completely independent mix from the same input channels. Each channel has a send level to each aux, so aux 1 might be the drummer’s monitor mix and aux 2 the singer’s, with entirely different balances.

The critical setting is pre-fade or post-fade.

• **Pre-fade** takes the signal before the channel fader, so the monitor mix does not change when you move a fader out front. This is what you want for monitors.
• **Post-fade** follows the channel fader, so the send rises and falls with the front of house level. This is what you want for effects, so the reverb on a vocal stays proportional.

Getting this backwards is why the drummer’s monitor mix changes every time you touch the desk.

Group: several channels under one fader

A group, or subgroup, collects several channels and gives you one fader for all of them. The classic use is drums: eight channels balanced against each other once, then the whole kit moved up or down with a single fader.

Groups can also carry processing applied to everything in them at once, which is more efficient and more coherent than the same compression on eight channels individually.

The output of a group is normally routed into the main mix rather than out of the desk, though most desks let you do either.

Matrix: a mix of mixes

A matrix takes existing mixes, usually the main outputs and the groups, and builds another mix from them. It is not fed from input channels directly.

That sounds abstract until you see the use cases, which are all about sending a variant of the main mix somewhere.

• A delay fill or a balcony zone, taking the main mix at a different level and time.
• A feed to a broadcast or recording truck, without the effects or with a different balance.
• A foyer or bar zone that needs the show quieter.
• A press feed.

If a job involves sending the show anywhere other than the main PA, matrix outputs are what you need, and small desks often have none.

Why bus count decides the desk

Add those up for a real job before choosing a desk. A band with four wedge mixes, two in-ear players in stereo, two effects and a broadcast feed needs eight auxes and a matrix, which rules out a lot of compact desks regardless of their input count.

This is the same reasoning as in Qu vs SQ vs Avantis, where the step up the range is largely about buses rather than channels.

Frequently asked questions

What is the difference between an aux and a group?

An aux builds a separate mix with its own balance. A group collects channels at their existing balance and puts them under one fader. Auxes are for monitor and effects sends, groups are for control and processing.

Should monitor sends be pre-fade or post-fade?

Pre-fade, so that changes to the front of house mix do not alter what the band hears. Effects sends should be post-fade so the effect follows the fader.

What is a matrix used for?

Building a mix of existing mixes, typically for delay fills, other zones in the building, and feeds to broadcast or recording. It is fed from outputs rather than from input channels.

How many auxes do I need?

One per monitor mix, plus one per effect. Count the actual mixes on stage, remembering that a stereo in-ear mix uses two, and buy a desk with headroom above that number.