There is a FUT mac for the ARC, I would give it a try and run the flash updater...

Greets @waedi. That update seems to be only for Intel-based Macs, whereas mine is Apple silicon...unless I'm missing something.

Hello @ramses. Do you mean keys on the keyboard, or via buttons on the ARC? It's possible that I might have accidentally pressed something because I had to suddenly move stuff around last night on my studio desk; I just wasn't aware of such commands. Do let me know.

Thanks!

It's something on the device itself in the menu SETUP/REV - Options - Hardware/Diagnosis.

How is the ARC USB connected to the Apple or to the UCX II?
On the UCX II there is one USB port which is shared for both functions, DURec and ARC USB.

Did you try to switch it from Apple to UCX II or vice versa?

I can't find this info about Intel only in the readme of the FUT,

this isthe readme :

RME  Intelligent Audio Solutions

ARC USB

USB Flash Update Tool for Mac OS X version 10.6 and up

This software updates the internal firmware of the ARC USB to version 7.

How to use:

Exit TotalMix FX. Make sure it is NOT running in background.

Hold down the buttons TALKBACK and DIM on the ARC USB while connecting the ARC USB. Then all LEDs should be lit a tiny bit. The ARC USB is now in programming mode.

Start the ARC USB Flasher app. If you did not follow the above instructions you will be notified to exit TM FX. If it doesn't find the current version number then the ARC USB is not in programming mode, see above.

If programming succeeds disconnect the ARC USB, exit the Flasher app, start TM FX, reconnect the ARC USB. Now go to Options / ARC & Key Commands Settings, tab ARC USB. In the lower right beside the Default Encoder Function list the info string 'SE-Mode' should show up.

-----------------------
Notes:

The ARC USB uses simple MIDI notes for its communication with TotalMix FX. Unfortunately there are some MIDI programs under Mac OS X that can not handle the flow of MIDI messages of the ARC USB, which causes dropped notes and other ill effects. The majority of problems is under macOS and with Logic, because it lacks any ability to select the MIDI port(s) it should listen too, but not exclusively.

A fix is to change from simple MIDI notes to SysEx messages. These are usually ignored, but will be recognized and used by TotalMix FX 1.6 and up.

For this to happen the ARC USB needs to be flashed to a new firmware version that adds a SysEx mode. We opted to not remove the former mode as older versions of TM FX would not work anymore. TM FX 1.6 and up will recognize the new ARC USB firmware version and SysEx mode (SE mode) will be used automatically.
------------------------

Copyright RME 02/2019. All rights reserved. Logic, Apple and Mac OS are trademarks or registered trademarks of Apple Corporation. RME, TotalMix FX and ARC USB are trademarks or registered trademarks of RME Germany.

Makes no sense to me that firmware update is needed, when the device worked ok already for a while and
the issue appeared suddenly from one to the other day.

Either USB sockets not seated properly or device damaged or the Mac got an update.

What do you think about that theory … ?!

To exclude the Mac fully ...

Can you test with the help of a friend to connect the ARC USB directly to the UCX II in standalone operation mode with no USB connection to the Mac?

Or can you check the ARC USB + UCX II on another Mac or PC?

EDIT: or try another USB cable to connect the ARC USB.

as ramses said:
Absolutely no need to update the firmware of the ARC USB

- first check, if its visible in Mac's system information app, in the USB Column (https://support.apple.com/en-ca/guide/m … r35536/mac)
- if so, plug it out of mac an close totalmix
- open AMS (Audio Midi Device App) and in Window-Menu select Midi-studio (or via ⌘+2)
- RME ARC should be greyed out (as nothing is connected) - select it, and remove it (via the "-" symbol or DEL-Key)
- reconnect it to Mac, it should appear directly in Midi-studio and being highlighted
- open totalmix and check again - if it still doesnt work, check your settings in totalmix

Would save lot of time, if you had mentioned the use of a 16 port hub in your first post.
And i wonder, how it should be related with your update to sequoia 15.1?

I don't know which exactly Hub you use. But a 16 Port Hub - I generally would not recommend this (especially the china products)

BTW: The ARC USB needs 160 mA max and ~0,3 Watts. What is nearly nothing.

Anyhow, i still wonder, why it worked before - but not now anymore with this (same) hub, etc. Would be just interesting to understand, what really was the issue.

Information that it happened after the OS upgrade would also have important to know,
because this is what changed from the one to the other day.

What is the status now? Does it work after your proposed changes?

To exclude the USB Hub as root cause disconnect it from the Apple computer and connect ARC USB directly to the computer.

I suggest to do this this before making any changes to the OS because if you perform multiple changes (the OS upgrade and changes in the macOS settings) and it should still not work, then you do not know whether the root cause is still the OS upgrade or something that you changed later.

For the next proposals I realise that this will probably require external help...

But I just wanted to put this idea forward. Maybe something like this can be implemented for the future, because problems like this could happen from time to time after OS upgrades. You should be prepared for this so that you can get back to work quickly if necessary.

So, If this troubleshooting doesn't solve the issue...
Do you have a backup which restores the system to the day before the upgrade?

Under Windows I have a disk image based backup of the SSD with the operating system.
In would have resolved the issue in two steps
1. make a disk image of the current non working state after OS update for later evaluation on a 2nd / external boot drive
2. I would restore the disk image of the day before OS update

3 advantages here:
a) if everything works fine after restoring the OS before the update then you know that it is no hardware problem
b) you can work again
c) you can boot from the external drive at any time for any further troubleshooting.

Once you know how to solve it on the 2nd OS installation, then make a backup of current main system
and perform the OS upgrade again and then fix any potential settings problem in macOS.

Just as you have to wear a seatbelt when driving a car, you should also make sure that you have implemented a tested disaster solution when operating a computer which, in the event of a disaster, restores a working state, if possible without loss of user data (separation of OS, user data on several partitions or physical discs).