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Input Trim Explanation


When using Axe Edit, what exactly does input trim in the amp block do? Is that what you change to "tickle the red", or is it used for something else? When would you want to increase or decrease it?


Power User
Basically, it's a control for the volume of the signal going INTO the Amp block, as if it were the Level parameter on a block immediately prior to the Amp.

It has no EQ (unlike the Input Drive), so it controls nothing except signal level (or "volume"). Basically, the higher it's set the harder your signal hits the front end of the amp.

Here's Cliff's post on Input Trim:

And his post on gain settings more generally in the Axe:
Both are required reading. For more general notes on Input Trim (which are very useful), see Yek's post above this one.
As to "Tickling the reds", and what you need to change to maximise that particular setting, that's the A/D converter input. TOTALLY unrelated to musical gain, that controls gain for signal-to-noise optimisation. It's basically a "set and forget" thing with your loudest guitar. Don't associate it with drive and gain in terms of playing, it's a hardware calibration sort of thing. It is described here:
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I recently tried attaching this to a controller, It works well to adjust the amount of gain wanted.
I use it across 4 scenes. Clean to lead.


Fractal Fanatic
The bright switch on many amps adds a treble bypass capacitor across the input gain or volume control of the amp. Because it is in parallel with the pot's output, the lower you set the knob, the more treble passes and the brighter the tone gets. It's the same basic idea behind a treble bleed capacitor on a guitar's volume knob. Input trim adjusts the level before this control, so it does not impact brightness the same way. Also, the input gain or volume control on most amps is after the first input tube stage, so its setting usually does not affect how hard the first tube stage is driven. Input Trim, on the other hand, is before the amp input, so it does affect how hard the input stage is driven. For amps that have separate high and low sensitivity inputs, like four input Plexis and many vintage Fender amps, the high sensitivity input is the one that is modeled and setting Input Trim to 0.5 simulates using the low sensitivity input.
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