Cubase 13 - "MMCSS priority cannot be set!"

Anybody else got this message anytime you first open and try to play a Cubase Pro 13 project with mostly VST instruments?
Never had this with Cubase 12

I have been getting the same on open!!!

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Hello, you find background and solution to this here:


YES! Thanks a lot! checking the box Use Device ‘WinRT MIDI’ under Studio ▸ Studio Setup ▸ MIDI Port Setup, fixed it for me. :blush:

S**t…Too soon… :confused: now it happens when i export the project…will have to try with MMCSS tool.

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Setting the Threads to 64 fixed it!. But I guess C13 is not optimized for 16 core CPU’s. -.- Weird that i never had this problem with C12 though. Same CPU and whole setup.

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Hi, great to read 64 is enough :slight_smile:

Just to clarify, this issue has nothing to do with core support in Cubase 13, which of course supports more than 16 and is also optimised for hybrid architectures as well.
This stems from a limitation to 32 threads with MMCSS priority set in the OS, when this limit is reached is of course system-specific, as it depends on the amount of cores in the system and the amount of MIDI devices/ports.

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Oh, I see, thank you for clarifying that. I also didn’t know Cubase is now optimized for hybrid architectures. That’s great to hear since I’m using Intel 13th Gen cpu.
Anyways,. Thanks a lot for your help! :slight_smile:

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Thank you for the link. Will setting the threads to 64 have any negative impact on the CPU, such as increased CPU usage? Can you elaborate on what exactly will happen as a result of making this alteration?

I use a Ryzen 7900X, and throughout the entire cycle with Cubase 12, I never encountered these errors; it worked flawlessly. Big projects, hundreds of MIDI tracks, no crashes, no audio dropouts. Now with Cubase 13 and the exact same computer specs and projects, I’m suddenly bombarded with these frustrating error messages.

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It has no impact on CPU consumption. What happens is that the OS limitation to 32 threads with MMCSS priority is lifted to whatever setting one decides to set. The article really explains everything in detail, including how and how many MMCSS Windows and Cubase create for each MIDI port and core on the system.

Cubase 12 had the same exact issue, as any other application that can use more than 32 MMCSS-priority threads on Windows: the only difference is that C13 warns the user instead of dropping performance, freezing or crashing (or better, increasing the chance of).

The only possible issues could occurr when running other applications that use MMCSS concurrently, which is not very likely.


Thank you for the explanation, setting it to 64 threads fixed it for me.

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