OK, sorry for the confusion, guys. Bear with me, as I've obviously still got some kinks to work out in my methods. I got too comfortable with the setup I was using since my other tests were seemingly coming out just fine. I was able to get some improved results in some regards (not all) by slightly altering my setup. Instead of plugging the SB1240 into my desktop, I used my Surface Pro (on battery). Most everything else was the same, including having the Gungnir's USB input fed from my desktop. I did a lot of experimentation with the gear and software I have available, and this was about the best I could do. As for that noise I heard when turning up my amp? Probably just a fluke and not from the Gungnir.

You will notice the results are much cleaner looking overall compared to what I posted originally. Firev1 had brought up the possibility of a ground loop, and it could have been something like that in my original tests. Either way, I've attached the revised RightMark, 24/96 results of the noise, DR, THD, and IMD tests. Basic, but it gets the point across (you can assume improvements seen here would apply to nearly all other tests I did).

As for the peak in the noise around 21KHz, I am really not sure. Someone with more knowledge in this area might know. This is most likely an artifact due to my setup, though it is possible something is wrong with this Gungnir (unlikely). Ultimately, this would need to be verified on better equipment, or, if it's just a matter of how the Gungnir and SB1240 (don't) work together, possibly even just a different ADC. I guess you can't expect every type of DAC and analog output stage to work with the SB1240's line-in. Considering firev1 had issues getting correct-looking results from some Modi measurements using the SB1240, I think it's most reasonable to assume this noise rise and peak is an artifact.

Despite getting much cleaner results, I still did not have luck getting better -90dB, 1KHz sine wave test results. Again, this is likely just an artifact, considering the Bifrost did a great job with it (see info in prior posts) and the Gungnir does show good results otherwise. However, I think the SB1240's ADC is capable of resolving this test to a decent degree, considering firev1's SB1240 loopback results (24/96 in particular, which I've been able to replicate) and my Hex results (I'm assuming the quantization steps are always expected to be seen on a NOS DAC in those tests, right?).

In the future, I'll do a better job double checking my results with a couple different setups to avoid producing "dirty" results again. I'll also leave out what appear to be erroneous results (like these -90dB tests), though something minor that can be noted and overlooked due to other redeeming qualities of the results (like many of these with that rise/peak in the noise) will likely get posted. I'll probably stop doing the sweep impulse-based tests as well. Interesting to experiment with, but I don't think I was providing useful info. But, again, apologies for the confusion and less-than-stellar work. (I'd go back and edit my posts if I had the ability to.)

Still, with these revised measurements, and taking the likely artifacts and other points into consideration, there's still some good information to be gathered:

- Frequency response results seem mostly accurate, tell us a bit about the DAC, and validate Schiit's published specs on their site. (The SB1240 will slightly alter the response, with one example being showing more bass roll-off than in actuality.)

- Noise floor is clean and low. I bet those small spikes and wiggles in the 60-300Hz range would be mitigated with a better environment and setup (i.e. USB not from a gaming desktop). Fluke or not, that noise spike around 21KHz still sits below -110dB. Overall, I think this validates Schiit's posted SNR specs. Dynamic rang e looks similarly great.

- THD measurements hit the limit of what the SB1240 can do, around 0.004%. Anything that hits this limit is already doing a pretty good job, and I see no reason to doubt the Gungnir performing to Schiit's specifications of <0.002% THD in actuality.

- JTest jitter measurements show a low, clean noise floor and sidebands that hit around -130dB. That's around the SB1240's limits, so the Gungnir should do an excellent job in terms of having low jitter (tested BNC and USB).

- RightMark pegs IMD at around 0.02% using the SMPTE test, but do note that Schiit lists IMD specifications in CCIR. I am honestly not sure how CCIF and CCIR differ. But, what I do know about CCIF tests is that I can get close to Schiit's posted IMD specification if I use the DFD2 CCIF results (a common method for CCIF measurements, I've read). At least, testing in that manner gets to the limits of the SB1240. But that might not mean much. Either way, I just wanted to point out why my IMD results will have discrepancies from Schiit's specs.

I knew full well with the SB1240 that excellent DACs would exceed its ADC capabilities and that some gear just might not measure 100% correctly on it. And that's OK when you keep everything in context, plus the SB1240 already performs quite well (much better than its price would indicate!). In other words, if it's maxing out the SB1240's limits, that gear probably already performs at a level of excellence to the point you need not be concerned if you like what you hear.

With these revisions and my noted points, I think these measurements overall validate Schiit's specs and prove it is an excellent performing DAC. I thought it had a lot of really good qualities to it in my listening tests! I think Marv and other pirates have done a good job describing its characteristics.

I need to re-do my SB1240 measurements, but there's some decent documentation on its capabilities in another thread here (combine the best results from myself and firev1, you'll get a decent idea...we were still working on our methods when we posted those results). Basically, it has a flat response with a slight bass roll-off, noise and DR numerically measure around -107-108dB (looking at the graph, though, you'll see the noise floor is clean and sits somewhere between -120-150dB depending on the setup and test), THD at around 0.0045-0.0035%, IMD around 0.004%, crosstalk around -98-100dB, can do a decent job resolving the -90dB 1KHz sine wave test, etc. One major limitation is that it can only do 48/96KHz sampling rates, at least on the RCA inputs and outputs. The SB1240's line-in might also be "picky" about input voltages, impedances, etc. Not sure...

Clearly, truly good DACs will hit the SB1240's limits, but I've made that clear from the start (I posted the SB1240 measurements as a reference point, though they need updating.). Once I got cleaner results, it was pretty clear the Gungnir was maxing out what the SB1240 could do in nearly all regards. Sweet, the DAC has objectively excellent performance and is likely operating as specified. That's good! Plus, we can learn a bit more about its performance characteristics.

When potential artifacts come up, it's good to pull from other resources. In this case, the Bifrost easily passed the tests on Stereophile, so it's almost guaranteed this is just one scenario where the SB1240 is producing some funky stuff that screws up a few, but not all, results and information. Best we can do is note that, keep the context in mind, and move on.

That said, I've still got a few ideas in mind to see if I can get better looking results. I doubt I'll make much more progress, but the Gungnir has been a good learning experience for me in terms of measuring DACs.