As walkintheseshoes suggested on 4/28/2021, I filed a support ticket for this issue on 5/15/2021, and I've been in almost daily contact with PreSonus Support on it since then. PreSonus has been consistent and timely in responding, though we've not established a root cause or resolution.
PreSonus policy prohibits sharing verbatim exchanges (which is normal in the industry), but I thought it could be helpful to share the actions they've recommended so far. This thread contains similar summaries, but my journey accumulated a few additional items. This way, if you file your own ticket for this problem, you may be able to save time by running through the procedures first. Make sure you tell PreSonus in detail what you've done, ideally with accompanying screenshots.
This list doesn't contain detailed instructions for each item. Google is your friend, and if you're not comfortable with what you find, wait on Support's instructions rather than anticipate their recommendations.
Many items on the list are applicable only to Windows systems.
* Register product at
https://my.presonus.com* Specify TB cable as part of system specs.
* Run System Information, save to .nfo file, and attach.
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Repeat this step after any system reconfiguration.* Ensure Quantum 2626 is default output device.
* Ensure all motherboard drivers and BIOS are up to date.
- Expect Support to check you on this, comparing drivers on the vendor site with what shows in your .nfo files.
- Don't rely solely on a vendor's update utility. For example, Gigabyte's APP Center is not always in sync with what's available on their website.
* Ensure UC and firmware are up to date.
* For each playback and recording device:
- Ensure "Allow applications to take exclusive control of this device" is disabled.
- Ensure all sample rate settings are identical.
* In Thunderbolt Control Center, ensure Quantum 2626 is approved and set to "Always Connect".
* Test Quantum 2626 in different computer if possible.
- For me, it's not possible.
* Manually uninstall/reinstall UC and associated devices.
- This is a little tricky, and I won't describe the details here. Best to do this under instruction from PreSonus Support. It did not help my issue.
- The procedure involves setting an environment variable. DO NOT unset the variable afterwards, because Support may misinterpret the missing variable in the .nfo file as not having followed instructions.
* Follow audio optimization steps here:
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https://support.presonus.com/hc/en-us/a ... rce=search* Use a utility called "DPC Latency Checker" from Thesycon to measure audio device latency. From what I can tell, the utility has been abandoned by the authors, but is easily locatable with a Google search. Given the apparent abandonware status of the tool, I'll leave it to the reader to locate the utility and ensure sensible malware protections are in place.
- My latency was typically around 1100us with occasional spikes around 1500us.
* Ensure GPU drivers are up to date.
* Consider resetting Windows 10 as described here:
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https://support.microsoft.com/en-us/win ... c1fbceb8dd - While I appreciate the potential benefit, I have not taken this step. I want to exhaust all other options first.
* Create a new Windows user and attempt to reproduce the problem logged in as that user.
- I experienced the same problem while logged in as the test user.
After all this, I put on my software developer hat (day job) and ran some diagnostic utilities that showed some interesting behaviors, but no smoking gun. Support folks are passing my results to the developers.