Setup help: REW with PC soundcard output and UAD Volt 1-channel, Dayton EMM-6

[thoraxe]

tl;dr: Can I use a 1/8-1/4 TRS cable from my PC sound card into my audio interface with +48V turned off and calibrate my PC sound card for REW, but still use an XLR mic with the +48V to take the REW measurements?

My PC drives a Yamaha AV receiver (2.1 setup) and I'd like to use REW to calibrate for my room. I don't have any sound treatment so the success will be limited, but sound treatment is coming, so why not start now?

The thing I'm trying to understand is how to do the sound card calibration with this particular setup, or if it's even required. Since my audio interface (UAD Volt) is not driving the speakers that will be used during the sweep, and the UAD is only used for the microphone (Dayton EMM-6), it seems that I would have to take the output from my PC soundcard before it goes into my AV receiver and run that into the input of the Volt to do the calibration/configuration. While I could use the headphone output on the UAD Volt to loop into the TRS input, I won't be using the headphone output on the Volt to drive the speakers during the test. The PC sound card is what normally drives my speakers, NOT the UAD Volt.

I _could_ switch the PC to use the Volt as the primary output, but then I'd have to do a lot of re-cabling as well.

* The PC sound card only has 1/8"-type outputs
* The Volt-1 has a TRS/XLR input with +48V phantom
* Using the EMM-6 requires enabling the +48V phantom
* I don't think I can use the +48V when running the PC speaker into the Volt
* I would need to convert the 1/8" connector to a 1/4" TRS, and the cable would end up being relatively long (~8-10'), and I'm not sure I can use a balanced cable in this setup

Can someone explain to me what the best thing to do is here? It seems like, at a minimum, I need to adapt the 1/8" output on the PC sound card to the 1/4" TRS input on the Volt to do the loopback for measuring/calibrating the sound card. There are many 10' 1/8-1/4 TRS cables on Amazon that could do the job.

* Is that all I need to do?
* Is it a problem that the +48v won't be used when plumbing the PC out into the Volt?

 

[AnalogSteph]

The most important calibration to be worrying about is that of your microphone. The contribution of your electronics tends to be relatively small in comparison:

The bass and treble rolloff also tend to vary with input gain setting, so you would have to set whatever you are typically using and reduce output volume in return... at which point things may end up so flat that you don't actually care in the realm of acoustic measurements.

For a loopback measurement you'd be buying a 3.5 mm stereo --> 2x XLR (male) cable, the length of which is quite irrelevant, and run it with P48V off (which should have no effect on FR whatever). Yes, you will have a ground loop, but no, it should not be severe enough to affect this measurement. Even if it does, you can generally resolder the XLRs to resolve the issue (remove pin 1-3 bridge and connect to 3 only). Or run the measurement between a battery-operated laptop with the Volt on it and the computer.

Results of sweeps can get a bit funky with two sound devices that aren't clock-synchronized, but you'll see. If push comes to shove, the more tedious noise-based measurement (preferably using pink noise so resolution down low doesn't entirely tank) may save the day.

 

[thoraxe]

Thanks for your input (pun intended). Would it be better to rig a temporary cable from the headphone or TRS outputs on the Volt to the amplifier to do the testing? That would eliminate any timing issues, I'd thing, since it's one piece of hardware doing both the input and output.

It seems like, either way, I need to get some cables for the loop back and/or the amplifier.

 

[AnalogSteph]

Would it be better to rig a temporary cable from the headphone or TRS outputs on the Volt to the amplifier to do the testing?

Theoretically yes, though it may not be strictly necessary.

Cabling required for loopback would be either 2 pcs. TRS to XLR or stereo 1/4" to 2x XLRm. You may already have a 1/4" to 3.5 mm adapter, one of those with a stereo 3.5 mm to 2x XLRm would see you prepared for either the Scarlett HP out or the onboard output.

 

[thoraxe]

OK, I got a TRS-RCA cable to run from the Volt headphone output to the amp, and a TRS-XLR to do the calibration of the headphone output.

I need to mess around with the settings of everything because I'm getting some noisy results. Will make a separate post about that.