This is comparison review and measurements of RME ADI-2 Pro against the RME ADI-2 DAC. The former has both analog to digital conversion in addition to digital to analog. I purchased that combo unit because I hope to make use of its ADC for measurements in the future. According to RME, ADI-2 DAC has some additional refinements in design which they say are not measurable. Well, I hope to measure them.I purchased the RME ADI-2 Pro by contacting RME in Germany/US and received kind accommodation pricing. With the retail price of USD $1,999, even with my discount, it is still pretty serious amount of dollars. The RME ADI-2 DAC which I reviewed earlier, comes at a much more reasonable price of $999.Physically the units are almost identical as far as size and general design:The rear of the unit is much improved though. Due to lack of space, connections such as S/PDIF on RME ADI-2 Pro are relegated to a dongle which sports rather pedestrian cable and connectors:Yes, we are not big on differences between cables in this forum but still, at $2,000 one expects a bit more polish here.On the RME ADI-2 DAC, space is freed up due to not needing inputs and everything has nice jacks on the back of the unit.For same reasons, inclusion of options for the input makes navigating the interface even more complicated than it is on RME ADI-2 DAC. Yes, you can get used to it and "auto" mode helps but still, this takes some getting used to. Repurposing the I/O button to simply cycle through inputs would go a long way toward making the unit more friendly to use.For this review, I am focused only on the DAC portion of RME ADI-2 Pro. The RME ADI-2 DAC is being returned tomorrow to its anxious (but patient!) owner so this is my last chance to see how they compare against each other.Let's get into the measurements and see how these two products compare. If you are not familiar with my tests, I suggest reading my tutorial on audio measurements here: https://www.audiosciencereview.com/forum/index.php?threads/understanding-audio-measurements.2351/ Unless noted, all measurements are via S/PDIF input. To add more information to the review of RME ADI-2 DAC, I performed all of these tests using balanced output. So the results are not directly comparable to the review of that unit.Let's compare jitter and noise using J-test signal at 24 bits, 48 kHz sampling:The results are identical (including a pair of jitter sidebands) except for broadening of the shoulders of our main 12 kHz tone. This indicates there is random, low frequency jitter in RME ADI-2 Pro which does not exist in RME ADI-2 DAC. Due to strong perceptual masking, definitely not an audible problem but a sign of a clock source that is polluted with noise. Seeing how I plan to use the ADI-2 Pro as my reference/benchmark DAC, this is problematic.If you look at the picture of the RME ADI-2 DAC, you see there is an "" after its name. I understand that may mean a "femtosecond" clock which is now also available in ADI-2 Pro. While accuracy of clocks is of no consequence in sound reproduction, if this new clock has lower random clock, it may be the reason the DAC version does better. And would fix this issue just the same in Pro version. I have to inquire from RME to see what is going on as I don't see any references to FS or femto clock on their website as of this writing.Thinking the above may be an issue with S/PDIF input, I also tested USB. The results were the same.Unfortunately this theme continued during the test of the tests. Let's look for example what happens when we feed a 1 kHz -3 dBFS to both DACs and then filter it out and see what is left over (all noise/distortion):Wow that is quite a difference. Strong odd harmonics are all but eliminated in ADI-2 DAC.Let's look at static linearity of the DAC by how well its analog output tracks the digital values fed to it:We again see a degradation in ADI-2 Pro. Thankfully the response stays sane all the way to -120 dB so strictly speaking still quite good. But it simply lacks the precision of ADI-2 DAC which is at the limits of my measurement gear.Intermodulation distortion was not as revealing of differences:But THD+N versus frequency was:There is 4 dB less distortion in the critical mid-frequencies.: the ADI-2 Pro was running at +19 dBu which produced the correct 6.9 volt output. The ADI-2 DAC however, was run at +13 dBu which produces slightly lower output at around 6.8 volt (from memory) which is incorrect. Maybe it needs a firmware update. Regardless, I tried matching the levels by dropping the volume by 0.5 dB on ADI-2 Pro but the results did not change.From the measurements, it seems clear that the RME ADI-2 DAC is very much improved over the ADI-2 Pro. This was unexpected. For audiophiles this is good news seeing how the DAC version is much cheaper anyway. For pros though, it seems like a loss to have a less performant DAC in the ADI-2 Pro subsystem.This leaves me personally in a quandary of not having a reference class DAC when I return the ADI-2 DAC to its owner tomorrow.-----------------------------As always, questions, comments, recommendations, etc. are welcome.If you like this review, please consider donating funds for these types of hardware purchases using Patreon ( https://www.patreon.com/audiosciencereview ), or upgrading your membership here though Paypal ( https://audiosciencereview.com/foru...eview-and-measurements.2164/page-3#post-59054 ).