I just stumpled over this thread on the Steinberg Cubase forum, which could bring some light into this.
Sounds to me that MMCSS would be nice to have, but that Microsoft changed / limited the implementation in Win10.
EDIT: URL of posting on Steinberg Forum that explains the topic/issues and links to the helpcenter article
https://www.steinberg.net/forums/viewto … p;t=117319
https://helpcenter.steinberg.de/hc/en-u … CPU-setups
As of Windows 10, the amount of real-time processing threads with Multimedia Class Scheduler Service (MMCSS) priority is limited to 32 per process - 4 of which are blocked by non-audio-threads already running.
In short, the outcome of this is that on systems built around a CPU with more than 14 logical cores*, processing threads exceeding this amount will be carried out as non-real-time (like UI-threads), introducing drop-outs and performance issues.
As long as no fix is provided on the operating system side, the following work-around will avoid performance issues and dropouts:
Option 1: Downgrade to Windows 8.1
Option 2: Limit the amount of cores used by Cubase/Nuendo to 14
There are mainly two ways of limiting the amount of cores:
Limit the amount of logical cores to 14 in your BIOS/UEFI (if applicable, please consult the motherboard documentation for details)
Limit the amount of cores used by the application's engine, here is how-to:
I could think of that this could be related to the issues that you experience with Sequoia under Win10.
There is also a link to a test program mmcss-test.exe
https://helpcenter.steinberg.de/hc/en-u … s-test.exe
which shows the amount of MMCSS priority threads and the amount of threads which failed to set MMCSS priority.
When running it on my Win7 system with Xeon E5-1650 (6 cores/12 threads), then there is no issue.
I tried even very high values of 8192 and 16384 which also succeed under Win7.
Careful: 16384 creates a lot of stress on your CPU, runs for 36 sec with 100% CPU load.
On Windows 10 (even the latest 1809, my upgrade succeeded before it has been pulled back my Microsoft)
it fails to support only 32 threads out of 128.
X10SRi-F, Win7 Prof, Cubase 9.5, UFX+, Octamic XTC, ADI-2 Pro FS BE/DAC, RayDAT, ARC USB