Check power profile to make sure nothing is allowed to go idle (monitor, hard drives, USB ports, everything). The clunk sorta sounds like the printer is shifting to standby.

Latest drivers for RME. Released last month IIRC.

The dpc spiking alone might be causing dropouts. You could try checking in Windows>control panel> device manager for any HDMI audio drivers relating to the graphics card being loaded and disable them (unless you jse audio over HDMI perhaps). Craig Anderton started a thread on HDMI graphics card drivers a while ago because he found disabling them solved some problems.

The clunk might be almost anything, especially of you have printers switched on. If the PC is allowing USB ports to go to sleep then for whatever reason waking them up that can cause a printer or drive to twitch a little. Sleeping USB ports might explain the UFX disconnects as well. Check the Windows power scheme has USB susoend switched off and also got through the USB ports and connections in device manager, call up their properties and disable USB sleeping there as well and see if that helps.

Finally, how are the PC temperatures looking? A PC without access to cool air and adequate ventilation can get quite hot quite quickly. A 1,000 watt psu gives off quite a lot of heat on its own and if that hot air gets drawn back into the computer or can't escape in the first place.....

Again, thanks everyone.
 
I've decided to go ahead and get a 1200W Corsair power supply. That and the USB over Ethernet adapters will be here tomorrow, and I'll let you know how I get on.
 
Power management is turned off on all my USB hubs. I'm using High Performance power settings with Sleep set to Never for everything. I manually put my machine to sleep when I'm not using it.
 
Using a short USB cable would mean hauling the computer out of the closet. Since I keep it there for noise reasons, I'm going to have to find a solution to use it in place anyway. So I'm going to try the USB over Ethernet.
 
I think that power conditioning would be my next step if the power supply and USB over Ethernet fail. However, the power in my studio is isolated from the AC and the rest of the house, so I'm not optimistic that's it.
 
I've got the latest RME driver, despite what my signature says (I can't get it to update for some reason).
 
The HD Audio drivers are disabled.
 
My Coolermaster case is very well ventilated, and my temperatures under load run a little over 40 C.
 
I think that covers all the suggestions. Sorry for not acknowledging and replying to everyone individually; it would be a lot of writing. Be assured all your input is much appreciated.
 
 

No matter what, you need to deal with the spike. Work on that while waiting for the parts. 
Normally a dpclat spike should not wack your drivers off line so it's not causing that issue, but you still want a stable machine with no spikes for running a DAW.
I myself had a bunch of weird issues and it turned out to be a faulty brand new power supply. SO that's a good move for sure. 

Thanks, Cactus Music. I'm not sure where to go with the LatMon output I've got, since the spikes appear to be in very basic and important drivers that aren't obviously connected with audio. But I won't give up.

Is it possible you have a WiFi adapter on this computer?  If so, these frequently cause significant DPC Latency Spikes that can really jack up your sound.  If you DO happen to have a WiFi adapter on the computer, you can quickly test out whether or not knocking it out of the equation fixes your issues.
 
So, what you would do it, right before getting ready to launch Sonar, temporarily disable the WiFi adapter (if there is a switch or function key on the computer for doing so), or if there is no such switch, simply go into Windows Device Manager, scroll down to where the WiFi adapter is, then right-click on it and click on 'Disable'.  (NOT Remove or Uninstall).
 
Once the WiFi adapter is disabled, launch your Sonar session and test it all out, keeping track on your performance and any dropouts or crackles and such.
 
When done with the Sonar session, close Sonar, then go back into Windows Device Manager and Enable the WiFi adapter again, this will open up access to the internet again, and all should be fine.
 
Please review the above, and if your DO have a WiFi adapter, go ahead and try the above test, and post back here with the testing results.
 
THANKS!!! :)
 
Bob Bone
 

Thanks, Bob.
 
No Wi-fi adapter. I've tried disabling my Ethernet adapters (and quite a few others) without seeing an improvement in LatMon.
 
BTW, I'm assuming that old DPCLat is still not compatible with newer Windows versions. LatMon indicates a peak up to 1 ms every couple of minutes. DPCLat shows a neat even row of bars, all at 1 ms.

Yes, DPCLat isn't compatible with Windows 8 onwards.

A pity because it's output when it does work properly is much easier to interpret than latmon.

Sorry if I'm asking the obvious here, but do you have the latest PC firmware version installed in the UFX? I'll happily admit I'm groping around for possible causes of the issues you're having so if I'm stating the obvious please don't take offence.

You might be on to something with the USB cable length, though I've tested mine for an hour or so and it seems to run happily using a 5 metre Belkin USB extender cable plus a 1.8 metre Belkin USB cable, which is a similar total length to what you are using. How much reliability at this kind of cable length depends on the specific cable and USB port I have no idea. When the UFX drops out is its USB connection light still lit? I'm wondering if the connection between the cables is the problem, or maybe a crack in a cable core.

I'm rather curious about how the UFX does with a USB/ethernet adaptor whether that solves the problem or not. It's a setup I've not come across before.

Thanks, tlw.
 
I've got the latest firmware for the UFX.
 
I'm guessing that the double-female adapter in my wall plate is at least as problematic as the length. I'm going to replace it with a CAT6 adapter which should be more robust. So I'll have a short USB cable to one adapter, a short CAT6 to the wall, a longish CAT6 from the wall inside the closet to the computer, then a final Ethernet to USB adapter plugged into the DAW. Might be better, might be worse. Just got the hardware about an hour ago.
 
The power supply should be here today too.
 
Watch this space!