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Clean boost overdrive into an audio interface

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Clean boost overdrive into an audio interface

Postby garrettendi » Tue Dec 22, 2020 12:18 pm

I know it won't harm the interface etc, but I'm thinking of using my Ultimate Drive (OCD clone) as a clean boost into amp sims on my PC/Mac straight into the interface.

Would this actually work? I would have though any boost in volume would be rendered pointless as I'd have to turn down the interface gain to stop any clipping?
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Re: Clean boost overdrive into an audio interface

Postby CS70 » Tue Dec 22, 2020 1:27 pm

No.

By definition an overdrive simply boosts the gain of your signal, to hit the front end of the (real) amplifier with a higher electrical level that would be normally produced by the guitar. It's "clean" insofar the gain setup does not exceed the headroom of the preamp, or otherwise some of the signal is filtered out or the boost is only applied to higher bands to the same effect.

With an interface, what you're hitting is the front-end of the A/D converter. It absolutely does not like being overdriven (i.e. seeing a signal which exceeds the max expected voltage of the circuit). "Clean" boost as just gaining up the amplitude of the signal - it's just the gain knob of the interface. Overdrive, you can't do it from outside.

So obviously you can use the pedal to boost the signal a little, so long you don't exceed the A/D circuitry headroom... but for that you can just as well use the interface's gain knob, which is probably less noisy than a pedal.

Note that it's different with distortions. Distortions work because they mangle the signal without necessarily overdriving it - but by other means. So the signal level can stay low but the circuitry changes it so that it sounds, well, distorted.

So distortion pedals will work (so long you keep the output level well within the A/D converter's headroom, as for any other source).

What you need if you want the same effect with a sim that you have with a real pedal is a... simulated pedal, that you "place" just in front of the simulated amp in software. The "pedal" will see the digital audio produced by the A/D conversion and suitably increase its level - if the amp emulation is well done, it will react like a real amp and get you that thickness and higher volume you expect.
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Re: Clean boost overdrive into an audio interface

Postby garrettendi » Tue Dec 22, 2020 1:30 pm

Yes I suspected as much.

I have in the past used VST pedals to achieve this and it's worked excellently, I was just hoping a physical pedal would work as well.

Thanks for the clear and informative response (not sarcasm)! :thumbup:
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Re: Clean boost overdrive into an audio interface

Postby CS70 » Tue Dec 22, 2020 1:33 pm

You're welcome :)
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Re: Clean boost overdrive into an audio interface

Postby Sam Spoons » Tue Dec 22, 2020 5:44 pm

IME many overdrives have a circuit designed to emulate a valve preamp clipping and can't supply clean gain like a booster pedal*, I believe the OCD is of that type. It's easy enough to try, turn the gain on the preamp down and up on the OCD so the level is similar (and the OCD is not overdriving the preamp) and see if it starts to distort. As CS says a clean boost will not work for the reasons he gives but an 'overdrive' pedal that does distort will impart it's colour into the input of the amp sim.

* Clean boost pedals are always marketed as such (TC Spark Booster, EH LPB-1, Seymour Duncan Pickup Booster) and some do both clean, frequency dependent (treble booster, and the SD Pickup booster has a switchable mid boost) and distortion.
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Re: Clean boost overdrive into an audio interface

Postby garrettendi » Tue Dec 22, 2020 5:48 pm

Thanks Sam, maybe I'll give it a try after all!
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Re: Clean boost overdrive into an audio interface

Postby Sam Spoons » Tue Dec 22, 2020 5:52 pm

:thumbup: Does no harm :D
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Re: Clean boost overdrive into an audio interface

Postby JRC1 » Thu Dec 24, 2020 9:17 pm

as someone new to computer music would sending a signal out of your interface and through a distortion or any other effect then back in work fine or would i come up with issues. obviously im not talking about a clean boost, but im yet to find a clean boost i have tried a lot and they always impart some tone on the sound.
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Re: Clean boost overdrive into an audio interface

Postby Sam Spoons » Thu Dec 24, 2020 10:14 pm

If you want clean boost from a computer interface/DAW system just turn up the gain. Sending from the interface to a guitar stomp box will need the output attenuating from the standard line level most output but will work fine if you do that*.

* The 'approved' method is to use a 'preamp' box but just turning toe level down may work just as well.
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Re: Clean boost overdrive into an audio interface

Postby ef37a » Fri Dec 25, 2020 7:56 am

Hi G! Happy Christmas day!
The high Z inputs* on many AIs do not have a lot of headroom (one infamously had next to buggerall!) and too much gain IMHO. Therefore you might even need an attenuator at the front end with a particularly hot humbucker or active guitar (although the latter could go into a Line input)
A truly clean boost is useful where you want to overdrive the first valve stage, few guitars can do that and avoid any "Transistor sound" or improve the S/N ratio of a noisy amp. (A well designed op amp HZ circuit will beat a triode for noise) .
A clean boost can also foil the screw up caused by that engineering nonsense the "True Bypass" pedal.

*This will not drive the converters directly, it will at least go through a discrete FET or a bifet op amp.

Dave.
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