Gsync compatible LFC issue

[yamaci1775]

For some reason with default refresh rate range, 48-146, I get weird out of sync refresh rate behaviour at low framerate caps. When I tweak the LFC lower range to 30 or 36 hz, it gets fixed and 30 FPS cap makes the screen run at 60 hz as it should. Mind you, I get physical stutters on the screen with the default setup.

Specs are: RTX 3070, Viewsonic XG2401, latest driver (551.86), latest Windows 11 build (23H2).

My driver settings are simple and as follows: "Enable for fullscreen mode"

Frame cap used in the video belongs to Special K, which I also used to monitor refresh rate of the screen (I don't know how it does it but it reflects the monitor OSD readout). I've tried a driver 1 year prior and I had a similar problem, so I wonder if it is a mix NVIDIA/Windows 11 issue.

I've tried disabling/enabling HAGS, MPOs, different combinations of both to no avail. I've also tried enabling driver vsync, no help.

With 30-146 range, game appears stutter free on the pysical screen. With 48-146 range, game constantly looks stuttery on the physical screen and quite horrible. Default range is 48-146 however and 30 FPS should just be able to sync to 60 hz without any problem. Increasing LFC range to something like 67-72 makes this problem even worse somehow (in that case, it shoots upwards of 93 hz constantly instead of syncing to 90 hz)



These are the default, non modified monitor settings as seen in CRU. When I tweak V rate to 30 or 36 from the 48, LFC starts working as it should at low framerates.

phpBB [video]

phpBB [video]

[Chief Blur Buster]

That's an interesting glitch...

Normally the best advice is to tweak LFC higher to a number such as 55 or 65.
However, sometimes lowering the minHz threshold actually helps certain VRR panels.

On some monitor models (not necessarily yours) making 60fps permanently LFC can sometimes result in better quality than native 60Hz (and avoid VRR flicker), so make sure you at least test this out. However, you have to weigh the pros/cons. The problem for your specific monitor model is that you don't have enough max:min range to raise your LFC threshold much, since you ideally need at least 3:1 max:min Hz in VRR range, for LFC to work properly.

LFC stutters from varying framerates are hard to avoid with low-Hz VRR. You ideally need 240Hz+ (or even 300Hz+) to reduce those low framerate stutters to negligible extents.

Do you get more or fewer blackouts with your current new LFC range?

Possible Workaround: A few percent larger vertical total (larger VBI)
Sometimes increasing the blanking interval size (avoid Reduced Blanking) and slightly reducing your MaxHz, will give your monitor more time (on the clock) to reinitialize between refresh cycles, and be less likely to blackout. However, there are many possible blackout triggers -- including Hz too low, Hz too high, and timings bad / blankings too small, etc. So you may have to try a larger Vertical Total to improve reliability.

[yamaci1775]

That's an interesting glitch...

Normally the best advice is to tweak LFC higher to a number such as 55 or 65.
However, sometimes lowering the minHz threshold actually helps certain VRR panels.

On some monitor models (not necessarily yours) making 60fps permanently LFC can sometimes result in better quality than native 60Hz (and avoid VRR flicker), so make sure you at least test this out. However, you have to weigh the pros/cons. The problem for your specific monitor model is that you don't have enough max:min range to raise your LFC threshold much, since you ideally need at least 3:1 max:min Hz in VRR range, for LFC to work properly.

LFC stutters from varying framerates are hard to avoid with low-Hz VRR. You ideally need 240Hz+ (or even 300Hz+) to reduce those low framerate stutters to negligible extents.

Do you get more or fewer blackouts with your current new LFC range?

Possible Workaround: A few percent larger vertical total (larger VBI)
Sometimes increasing the blanking interval size (avoid Reduced Blanking) and slightly reducing your MaxHz, will give your monitor more time (on the clock) to reinitialize between refresh cycles, and be less likely to blackout. However, there are many possible blackout triggers -- including Hz too low, Hz too high, and timings bad / blankings too small, etc. So you may have to try a larger Vertical Total to improve reliability.

I don't get any blackouts at all with the new LFC range. My actual problem is, I didn't need such a tweak before to get 30 FPS>60 HZ LFC sync. 1 year ago or so, I played The last of us part 1 with the same 30 FPS lock and it used to perfectly synced to 60 hz without any CRU tweaks (I retried that game and same problem happened there too). I tried going back to drivers 1 year prior but that didn't help the issue either. So it could be that something related to Windows 11 updates related to WDDM. And there's no way for me to go back to W10 or find the specific update that might've caused it.

Technically I should not be subject to LFC stutters at all, since I'm in the constant LFC zone (30 FPS - 60 hz). I'm playing at 30 FPS, not 60 FPS.