The most-asked and worst-answered question about this unit. Five stages, in order, and the resolution of the advice that appears to contradict itself.
Search this question and you will find two camps. One says leave input gain at 0.0. The other says set it just below clipping. Both get repeated, neither gets reconciled, and the question keeps coming back.
They are not opposing positions. 0 dB is the default — the unit is built to take a hard-strummed humbucker there without clipping. “Just below clipping” is the verification — the check that confirms it holds for your guitar, and the adjustment you make if it does not. One is a starting point, the other is a test. Do them in that order and there is nothing left to argue about.
Swipe down from the top of the screen → I/O Settings → select the input
Start at 0 dB. Only move it if the meter says to.
The unit is designed to take a hard-strummed humbucker without clipping at 0 dB. For most guitars this stage is already correct and needs nothing.
Quad Cortex Wiki: Gain Staging · Quad Cortex Wiki: Setting the Input LevelSame screen, watching the meter while you play
Play a little harder than you normally would. The meter should just tickle the red, or sit just below it.
This is the check, not a second opinion. If a hot pickup buries the red at 0 dB, pull the level down until it only tickles. If a weak single coil never approaches it, you have headroom to spare and can leave it alone.
Quad Cortex Wiki: Setting the Input LevelOn the Grid, at the end of the row
0 dB as a baseline, then adjust for headroom.
This is where preset-to-preset level matching actually happens. Leave 12 dB of headroom on clean patches and 6 dB on distorted ones — clean tones peak far above where they feel like they do.
Quad Cortex Wiki: Gain StagingI/O Settings
0 dB.
Set the baseline here and leave it. This is a device-wide trim, not a per-preset one.
Quad Cortex Wiki: Gain StagingThe one physical knob
Maximum, while you set everything above. Trim from there for the room.
With the knob maxed, what leaves the jacks matches what the meters show. Setting levels with the knob halfway means every meter on the unit is lying to you about what front of house receives.
Quad Cortex Wiki: Gain StagingHeadroom: 12 dB clean, 6 dB distorted
Clean tones have a far higher peak-to-average ratio than distorted ones — distortion is compression, and a saturated patch simply does not spike the way a clean one does. Setting both by ear at the same apparent loudness is how clean presets end up clipping in the room.
The output meter and the lane output control live on different pages. There is no view that shows both, so the obvious method — nudge the control, watch the meter — is not available.
Do thisTurn the lane output up until it flashes red, then back it off a known number of dB. You are measuring by finding the ceiling rather than by watching the needle.
Quad Cortex Wiki: Gain StagingThe quarter-inch outputs are balanced. Plug an unbalanced TS cable in and you get half the output voltage.
Do thisUse TRS into balanced gear. If the destination is unbalanced and TS is the only option, add 6 dB to get back to unity — and remember you have spent 6 dB of headroom doing it.
Quad Cortex Wiki: Gain StagingIt is not saved with a preset and a scene cannot recall it. Swapping between a Les Paul and a Strat mid-set means the input stage is a compromise for one of them.
Do thisSet it for your hottest guitar so nothing clips, and make up the difference with a gain block inside the presets that need it.
Quad Cortex Wiki: Gain Staging · Quad Cortex Wiki: Setting the Input LevelDigital clipping does not soften the way analogue clipping does, and reaching for a limiter to control an over-hot chain trades one problem for a worse one.
Do thisFind the stage that is too hot and fix it there. Headroom is cheaper than repair.
Quad Cortex Wiki: Gain StagingUnity out of SEND 1 and SEND 2 is line level. Most pedals and many preamps expect something a lot quieter.
Do thisPull the send down for unamplified devices — around −5 dB is a reasonable starting point, then trust your ears and the device's own input meter.
Quad Cortex Wiki: FAQ