Hi @DaveD, thanks for the update! I think the focus should be getting 48k pristine, and then moving on to other sample rates. The USB code in the releases hasn’t been touched in a long time, so I don’t think you’ll see a difference bouncing between the various recent releases.
First, can you verify that the USB voltage reported by the QA40x app isn’t showing orange or red? This can be done with a 20 awg cable as you’ve done and if that isn’t solving the issue completely, then try using a powered USB hub.
Second, if you are still having issues after that, I’d see what it takes to update the BIOS and motherboard USB drivers. I know that’s a pain, but something in your current desktop is probably responding slowly to USB packets arriving and that is causing the apparent loss of data.
Next, re-start the app, do a File->New Settings, set the FFT size to minimum, enabled GEN1 and just let it run in loopback while you do other things on your machine. It should run for 10’s of thousands of acquisitions (which will take maybe 30 minutes) without any problem with a consistent spectrum. If packets are lost, the spectrum will turn to garbage and often won’t recover right away so it’s easy to see.
If the issues at 48k can’t be solved, then the issues at higher sample rates won’t be solved either. And so, the 48k is a good place to start. I know you did 27 tests without errors, but the aim should be to do 10’s of thousands of acquisitions without an issue. Remember as shown above the counter in the lower left to help you keep track.
Please report back what you find when time permits