As requested, I went to test the HD12 using Coax input. To my surprise, performance shot way up! I couldn't figure out how the different digital input would make such a difference. So I went back to testing USB and could not. The ASIO interface I was using would not recognize the HD12 anymore. Could not use ASIO4ALL since it would truncate to 16 bits. So I used Roon to stream the same 1 kHz tone using WASAPI interface and got the same improved performance as Coax!
Somehow the other ASIO interface must have been converting 24 bit samples to 16 bits but with dither added. That would limit the performance to 93 dB which is what we got. The revised ranking is now much healthier:
I wanted to repeat the rest of the test so I resorted to using Coax from here on. Note again that the above was with USB and there is no difference between USB and Coax.
Linearity was much improved now:
Jitter lost its previous aberrations but got a new one:
There is also some close-in jitter around our main tone that should not be audible due to perceptual masking.
I was pleasantly surprised that the HD12 accepted 192 kHz input for multitone testing as most DACs cannot:
Dynamic range did not change since it would not be impacted by the driver issue:
Improved noise performance translated into lower noise in headphone output as well:
Power output remains low and non-competitive though.
Conclusions
I have gotten bit by the restriction in Audio Precision software to only work with ASIO interface a few times in the past. This is another case. It is a shame they are not investing the work to support Wasapi. Regardless, I was the one publishing the tests and passing judgement on Hegel HD12 DSD and will fall on my sword.
I apologize for the first set of erroneous results. I will update the review to put a link to this updated results.
Some conclusions remain though. You can do better in every performance and build quality front with modern combo DAC and Headphone amplifiers. Build quality is simply not there with HD12 DSD. These issues aside, the performance of HD12 DSD is now solid and so if you have an affinity for the brand, I don't see issue with buying one used at a good price.