I’m recording an electric guitar line-in (no effects) via an ART Digital MPA preamp. It sounds OK when played back in Audacity but the waveform looks clipped at .25 on the vertical scale? Very odd. Here’s a screen capture …
Right. Massive clipping. If you play fuzz guitar, you get that by taking a clean guitar and apply massive clipping. Little or no difference which is why you can’t hear it.
Plug the guitar into the Instrument or Line connection of your interface. Not the Microphone connection.
I hope it has one. I don’t see it. Consult your instructions.
Koz
Yes it does look clipped.
What’s the exact model of the Art pre-amp? I thought the MPA was a microphone pre-amp.
I thought the MPA was a microphone pre-amp.
I think that’s the problem…
Koz
The ART Digital MPA has everything. From a nice high-Z guitar input, some tubing, and even an ADC on sp/dif, ADAT or AES out…
This is the newest, the MPA II:
http://artproaudio.com/mic_preamps/product/digital_mpa-ii/
So, I’m guessing the OP is using it over sp/dif optical?
So, I’m guessing the OP is using it over sp/dif optical?
That’s possible, but the distortion is happening way before that. How do you access the guitar connection? There’s nothing on the case to tell you what to do. It’s possible that’s what the “Insert” connection does. But it’s more likely that will give you RTS version of Mic-In (Rock Band Microphone), which, by extension is likely where the clipping is coming from. If the poster adapted the guitar to the XLR connection, that’s definitely where it’s coming from.
Koz
According to the owner’s manual, there’s a switch:
Cool. So this is where okieman drops in to tell us what he did.
Koz
There’s a separate instrument input on the front, marked “Hi-Z”…
But there’s also a knob with digital gain. Which is confusing. Supposing the digital gain is up to +10 dB, this could be the source of the clipping, if used together with a very hot guitar pickup.
Turn off the 20dB boost if that’s got turned on by accident. That will create bad recording conditions for a guitar.
Guitar and Stereo Line are cousins of each other and a guitar will work in either one. The angels will not smite thee if you cross them by accident.
As an experiment, I borrowed one of the digital artist’s excellent electric guitar and jammed a scope in the connection instead of an amplifier. If I really hogged down on a major chord, I could almost reach 0dB—stereo line level. The artist said he routinely plugs into the stereo connections of equipment with great success and that’s how he was using it in his office.
Connecting a guitar to a Mic-In will destroy the sound which is why that was my first guess. But yes, it’s easy to misadjust the controls on this amplifier. It takes sitting in the corner with the instructions.
Koz
(Sorry I was away.) Yes, I’ve been using the Hi-Z 1/4" input on the front panel. I thought that was correct for a standard line out from a Strat? This ART DMPA is the first one before Roman numerals II etc. The front is plain silver color. It’s late at night here so I’ll have to come back to tinker with the gain to see if that’s the glitch!
Just for an overview, I’m betting we all think his setup should work very well. Nothing jumps out as a connection mistake. I think I’d be doing it just exactly the same way you did.
It is a puzzlement why it doesn’t work.
There is one problem. Give us the address of the information for the one you own. All I can find is the II model.
http://www.sweetwater.com/store/detail/DigitalMPA2
I read over the thread. How did you, in detail, connect this thing to the computer?
Koz
OK the advice here has officially solved my problem!
I’ve owned this preamp for a number of years and just never run into a config that would make it clip. Probably qualifies a user error, doesn’t it? 
With apologies to Koz for my response delay, the connection was plain old Guitar> Preamp_HiZinput> PC_soundcard
and here’s the ART link to their doc as a PDF …
http://artproaudio.com/downloads/owners_manuals/om_dmpa.pdf?v=1429131451
(No idea why they omitted the face page for this doc. At least the guts are there.)