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Old 03-08-2017, 01:38 PM   #1
matthewjumpsoffbuildings
Human being with feelings
 
Join Date: Mar 2013
Posts: 463
Default Phase inversion noise floor trickery?

Ok this is going to be long winded...

Im using amp sims a lot, and while they sound pretty good, one thing thats always bugged me is the higain sounds amplifying my digital preamps noise floor.

While my preamps are not bad (with the volume turned up to adequate levels on my Presonus Digimax HiZ input, the noise floor is around -80db), once I add an amp head sim with a distortion pedal, you can really hear that harsh digital noise being amplified. Even if I dont have a guitar plugged in (or the guitar volume turned off), the actual white-noise-ish sound of my preamps noise floor is still super audible.

Im aware you can gate the signal chain going into the amp sim, but theres 3 problems with that:
1. it affects the attack of notes, especially the first note after a pause
2. it messes with sustain, and often when on the tail end of the gate the noise becomes really audible again
3. a gate is really just a fancy on/off switch, and when its on, that white noise is going to be part of the signal and adding its nasty brittle sound to the tone

So - i was playing around a little with phase reversal, and I discovered, no surprise, that if you feed the amp sim with 2 copies of the input track, one with the phase reversed, you get no digital noise floor. Of course, you also get no sound at all :P

But it got me thinking, what if you could feed the amp with a normal input, and then a phase inverted noise floor from a second input channel on the preamp. So I tried that, and of course that didnt work, because the noise on each input is random/unique, so the phase inversion didnt cancel anything out

So then I started thinking, what if i feed the amp sim with 2 copies of the SAME input, one of them phase inverted, but on the phase inverted one, do some kind of trickery so that when the volume of any frequency crosses a certain threshold (eg just above the natural digital noise floors level), it doesnt get any louder. Which would mean that it WOULDNT cancel out the normal (in phase) input feeding the amp sim. So then only the noise floor would get cancelled out, at all times, which would be amazing.

The big question is what kind (if any) of dynamic processor could I use to do this? basically what I need is something that can have a threshold, and stop any frequency from getting any louder than that threshold BUT not turn down the volume of the other frequencies in the signal AND not add any extra harmonics/distortion in doing so. Oh and it would have to be as close to realtime as possible, a buffer of 32-64 samples is ok but not much more... is that even possible? It sounds impossible but doesnt hurt to ask.

The other way I can think to do this is somehow in the hardware realm of digital preamps get access to the exact noise floor signal of a specific channel BEFORE the actual input signal is added to it, so then you can phase invert that and remove it, but Im guessing thats even more impossible or all preamps would be doing that already for completely noiseless gain :/

I hope this makes sense to somebody
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