Can't change screen refresh rate on M1 MBP

Discussion in 'Installation and Configuration' started by insanityfarm, Nov 5, 2021.

  1. insanityfarm

    insanityfarm Bit Poster

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    I set up my first Windows VM on my new M1 Max MBP the other day, and for better compatibility with old games I went searching for a way to lock the VM's screen refresh rate at 60Hz. I was unable to do this anywhere in Windows settings, in every place I know to look 120Hz was the only option available. I read somewhere that Parallels just passes the host refresh rate through to the guest OS, so I tried lowering it in macOS System Preferences.

    Weirdly, even with the Mac at the lower rate Windows continued to run (or at least reported it was running, I didn't confirm) at 120Hz, even after I restarted the VM, relaunched Parallels, and rebooted my Mac. So I reverted the Mac refresh rate to "ProMotion" (120Hz) and rolled back to a VM snapshot I'd taken before beginning this process.

    What surprised me was that once I did that, Windows was locked to a refresh rate of 60Hz! I have no idea how or why. Unfortunately, now I don't have a way to put it back the way it was. I confirmed my settings in System Preferences and rebooted the Mac. Windows reports that "Generic PnP Monitor and Parallels Display Adapter (WDDM)" only support 60Hz now. When I created this snapshot it was still 120Hz, and I have no earlier snapshot to roll back to. It looks like it's stuck like this.

    Full disclosure: Before lowering the macOS refresh rate, I'd been experimenting with Custom Resolution Utility inside the VM. I don't really understand what that tool does or how it works. I was careful to create my snapshot before messing with it, so I could roll back if anything went awry. It didn't appear to work at all; after all my changes Windows still reported 120Hz. Then I went did the stuff I described above. Is it possible that CRU made a change to the VM that persisted after snapshot rollback? Or is that a red herring?

    Can anyone help me get my VM to use 120Hz again? Bonus points if you know of a way to toggle between refresh rates at will, for those old games that need it.
     
  2. insanityfarm

    insanityfarm Bit Poster

    Messages:
    2
    I just found this knowledge base article which says Windows settings in the VM will always show 60Hz on a 120Hz screen, but that's not actually correct. At least not in Windows 11. Just to confirm I'm not imagining things, I spun up a new W11 VM and took a screenshot (attached) of the "120 Hertz" option. That's the only option available, but it's gone from my original VM, replaced with "60 Hertz" only.

    Is there a way to reset the adapter or something, to revert back to its initial state? Or should I just ignore this (like the KB says) because Windows is actually using the correct refresh rate and just misreporting it?
     

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