I described what I heard, I gave you measures black and white to suport that. Problem wasnt the device but stupid manufacturer decision. There is objective truth
Well, I don't think that can be qualified as "truth", since it all starts from "what you heard".
The DC filter being the device default, and the (documented) fact that it alters the frequency response below 20Hz (with a negligible impact at 20Hz) are both facts.
The problem starts when you state you can hear an audible difference driven by that.
First, we all know subjective listening is very much subject to strong non conscient bias.
That's why the golden rule to scientifically validate such listening differences is repeated (double) blind test, under controlled conditions, checked for statistical significance.
Of course, there may be obvious changes that can be identified 100% of the time, and for which DBT would just be a waste of time.
But if that's the case here, we need to find the root cause of those differences, since, for sure, the cause is NOT the RME DC filter.
The only thing the DC filter can be is a CURE to a pre-existing problem. That's what it's designed for.
So, as I suggested, we should look at the music content you hear this difference with, and at the whole system, to find where the issue is.
When this will be understood better, you should be able to measure this effect and re-create it if you want, but on purpose, not by accident.
Because, what you hear, if there is actually something to be heard, is a component acting as an effect engine.
That's not "fidelity", like in HiFi.
Then comes the problem I have with your tone, from the beginning.
Why are you so aggressive ?
And you state something but don't mind to explain the context (music, rest of the system, howyou proceed to compare,...) that could help us understand and identify where your experience comes from.
Did you, as an example, at least match the output levels when comparing ?
We know that level difference is even more impacting the subjective impression than changes in frequency response.
Not to speak about change in
FR below 20Hz...
It may seem cool to a newcomer to criticize a reputable manufacturer here to gain attention, but that's not what this site is about.
It's about learning, having fun, and collaborative effort to increase everyone's knowledge.
So, unless you're truely seeking for help to identify where all this comes from, without prejudice and in full respect, I think we should stop here.