Hardware & signal path
Aux input
An aux input is a spare line-level input for a source that is not a deck: a phone, a laptop, a sampler, a guest’s interface. It usually has less control than a full channel.
In practice
Find the aux before doors, not during a changeover. It is the socket that rescues a guest with the wrong gear.
On most four-channel club mixers channel four doubles as an aux with a 3.5 mm or RCA option; some models put a dedicated mini-jack on the front. Where there is no gain control, set the source device to roughly 80% output and leave yourself somewhere to go rather than starting at full and discovering you have no headroom. If the aux has no EQ, borrow the mixer’s master isolator or accept that you cannot bass-swap out of it.
Line
The level it expects
Ch 4
Where it usually hides
~80%
Source output to start at
Where these come from: Layout conventions across common club mixers and a practical starting level — not catalog figures.
Why it matters
It is the socket that saves a changeover. A guest arriving with a laptop and no interface, a track that only exists on someone’s phone, a live act needing one input for a backing track — all of it goes through aux, and knowing where it is on an unfamiliar mixer is a two-minute job you should do before doors.
The catch is that aux inputs are frequently unmetered and sometimes unfaded, so a phone at full volume arrives with no way to trim it except at the source. Set the phone or laptop first, then bring it up, rather than the other way round.
Frequently asked
Can I plug my phone straight into the mixer?+
Yes, into an aux or line input with a 3.5 mm to RCA lead. Never into phono, and set the phone’s own volume before you raise the channel.
Why does the aux sound quiet?+
Consumer outputs run several decibels below professional line level. Raise the source device first, then the channel gain, rather than pushing the fader past its normal working range.
Does aux go through the effects?+
On a club mixer usually yes, because the effects sit on the master or are assignable per channel. On a simpler mixer the aux may bypass everything, which is worth checking before you plan a transition around it.
Related terms
Mixer channel
A channel is one vertical strip on the mixer and everything one source passes through: input select, trim, EQ, filter, cue, and the fader at the bottom. The controls act in that order from top to bottom.
Phono input
A phono input accepts the tiny signal a turntable cartridge produces and applies RIAA equalisation to it, boosting the level by around 40 dB and restoring the bass that was deliberately cut when the record was pressed.
Mic input
A mic input takes the very low signal a microphone produces and amplifies it to line level, with its own gain, usually its own two-band EQ, and on club mixers a talkover control that ducks the music while someone speaks.
Signal chain
The signal chain is the ordered path a sound takes from file to room: player, mixer channel, master, amplifier, speaker. Each stage has its own level and can only pass on what the last one delivered.
Explore: Planning a b2b set · Mixer channel · Line level · All DJ terms