I don‘t see a reason to delete this posting, I already wanted to answer and then it disappeared.
Are you sure you didn’t accidentally delete it by yourself?

I had a look in my own archive, but all I have is:
ADI-2 DAC FPGA 27, DSP 33 from 2019-10-14
ADI-2 DAC FPGA 78, DSP 48 from 2022-01-19

What’s so special about the version you ask for?

EDIT:
Here’s an official list with links to most published firmware versions (some links are heading to other than the denoted FW):
https://forum.rme-audio.de/viewtopic.ph … 80#p143080

The link list I pointed you at is intended to serve for what you’re asking for.
Unfortunately for the exact version you want the link heads wrong.

To find out which FW version sounds maybe marginally different is out of my scope.
The only way for me to find out would be, to blind A/B two identical ADI-2s.
The time it takes to do the updates simply is too long for a valid comparison.
Even when the “improved” FS Clock came out I didn’t notice any obvious sound difference, although I used my ADI-2 Pro a lot, before and after.

Even if it sounds trivial:
you won’t need to use the extended range of B/T.
Personally I like and use it, and having B/T fully integrate it into the PEQ now is a big step forward for my use case.

@MC:
If you find some time it might be worth to fix the broken links.

Okay, sorry. Yea I recieved the file this morning from support. Was unsure whether I'd recieve any response since from my experience the people checking mails are often advised in certain ways regarding certain questions so unsure how they'd go about an older firmware request and seen people have had success here in the forum but yea should have waited longer before contacting both ways, my apologizies.

From a quick comparison I think I've found one setting that might have had an influence on how I felt regarding the sound difference in the latest firmware. In the newest firmware there is a new setting "Dig DC Protection" setting in the I/O section, by default this was set to "Filter" but turning it to "On" (or Off) it sounds ever so slightly better to me and puts it roughly on same level comparing the two firmwares. Reading the description I suppose it could have a tiny impact on the sound but I don't think many people even notices the difference as it's a fairly small one. Personally I'm a hobby mastering engineer that have mastered over like 2000 tracks probably so I've gotten quite used to spotting tiny differences, both a blessing and curse when it comes to audio as you are always listening for tiny details sorta instead of just enjoying the music.

Anyway thanks for your help

The difference I'm hearing is probably not what it's supposed to do but rather some side effect I'm guessing that comes with the filter. You know a bit like comparing one EQ to another the end result with same adjustment is typically not entirely the same as they do it with slightly different end results why for example this DAC's parametric EQ will be better than your "onboard sound" built-in EQ that sounds horrible in comparison if doing more than some 1.5dB adjustments with obvious non-wanted distortion.

I'm using headphones, a pre-amp and this DAC. The difference comes best forth in EDM music where the beats come across as slightly more punchy & dynamic sounding, the body of the kick sorta stands out a little better in the mix if turning the Dig DC Protection to "On" rather than "Filter" setting. It's a pretty similar difference as comparing the DA filter SD Sharp vs SD smooth setting for example.

Anyway this device is a fantastic tool in what I use it for, definitely among my best purchases ever.

I can confirm from my experience in studio work that High Pass Filters outside the audio band can have an impact on the sound.

My hypothesis is, these signals are so slow that they are not received as frequency, but as single events.
If you remove these events it will have an impact on the sound.
One needs speakers or headphones (like the early models from AUDEZE) that are capable of reproducing these frequencies to perceive the difference.

... for example

Seriously:
Every percussion instrument produces subs.
Percussion is based on a single pulse, the hit on the instrument.
Physically a pulse contains all frequencies down to DC.
Vocal plosives in front of a mic are another example.
Electronic sound contains subs quite often, even more so if produced in the digital domain completely.

Remember the DC content discussion that led to introducing the DC Filter in ADI-2.

Several circumstances filter them, like the size and resonance of the instrument, the cutoff of microphone and, on purpose, the preamp etc., but never completely removes all sub low content (filters have limited steepness).

The DPA 4003 mic, commonly used for drums, percussion and as main mic for classical, is defined down to ~2 Hz e.g.
https://www.manualslib.com/manual/80008 … =12#manual

Using an FFT Analyzer reveals a lot, you will be astonished.

Of course, this is why we try to remove them, usually on a per track basis during production, if their amount is significant.
My studio monitors reproduce subs enough to give me a warning sign.
Usually it’s a single event that I edit out.

But this time the signal is not outside humans ability to perceive, if you speakers system is capable to reproduce it. 

This is why we try to remove it.

For vinyl e.g. subs are an absolute no-go, remember the famous Overture 1812 recording where the canon shots can throw the pickup out of the groove.
It’s sold a lot of copies only for that “feature”

Here’s a microscope foto of the groove:

KaiS, the DC filter did its job and cut something out, it is the actual difference when it applied, I believe some people can hear it and some not. For safety purpose, I leave the filter on.

That’s exactly what’s been the question for me, and what made this thread start:

Are frequencies below 7 Hz audible?
My answer, despite “common knowledge”, clearly says - yes.

Of course, the music must contain them, and you need a system that is capable of reproducing them.

Seems contemporary music production quite often contain such frequencies, my 2nd music example wasn’t specially selected, but the first title from the “What’s New This Week” playlist in Tidal.

On my Mysphere 3.2 I don’t hear a difference, such low frequencies simply are not reproduced there anyway.

For the sound, better or worse, I can’t decide.
For me it simply doesn’t matter.

I have Dig. DC Protection “ON”, but not the “Filter”.
Warning screen was never triggered since, might even be because I have an typical listening level of -30 dBr or less.

For those listening to ill-processed sources like the originally mentioned internet radio channels that led to introducing the option, the filter is a great relief for sure.