[Otto]

Hi Blue,

Oh, I thought you had already calibrated it with an analog loopback. I don't think it's possible to properly calibrate your soundcard using the digital I/O because you'll be using analog input when you do your measurement (because the input signal be coming from an analog mic).

What I did was calibrate my soundcard using analog I/O. After doing that, I was able to measure an analog loopback sweep, and it was perfectly flat (with the calibration file applied, of course). Then, in place of the simple analog loopback test, I inserted a preamp into the path. I measured analog frequency response of that preamp (flat, with cal file applied). Then I measured the frequency response of the preamp with a digital signal from my PC (using the preamp's analog outputs). The measured response (using S/PDIF into the preamp, analog out) was generally the same (i.e., identical) to that of the analog input.

For me, that was evidence enough to use the calibration file for either. Also, it tells me that the correction needed for the frequency response of the soundcard is generally in the input stage of the soundcard, and that the output stage doesn't have that much negative effect on FR. I'm not sure that I would necessarily expect that, but that's what I recall.