Asus VG259Q and stutter with LFC

Talk about AMD's FreeSync and VESA AdaptiveSync, which are variable refresh rate technologies. They also eliminate stutters, and eliminate tearing. List of FreeSync Monitors.
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Asus VG259Q and stutter with LFC

Post by Spedemix » 11 Jun 2021, 03:26

Hi. Recently bought an Asus VG259Q, my first Freesync monitor so I'm a bit new when it comes to the VRR stuff. It's connected to my GTX 1060 3GB with DP cable. As far as I've understood the monitor is G-SYNC compatible so it should work pretty well. I'm running the latest Nvidia driver (the one that came out a day before writing this topic). Using Windows 10 2004. I'm running the G-sync compability "for fullscreen and windowed applications" since some of my games don't have exclusive fullscreen modes and it seems like fewer and fewer games have those as time goes on.

VRR works great with this display - as long as i run games at over 72Hz. You see the moment I drop down to say, 60fps, LFC kicks in and ups the screen refresh rate to 120Hz. And that's when I start getting pretty severe stuttering.

The thing is, it doesn't matter whether I run VRR with LFC or try to view a 60fps video using a static 120Hz mode, I WILL get heavy stuttering. All the stutters at 60fps go away when I drop the monitor refresh rate to 60. So basically whenever the fps/Hz ratio is 1/2, I get stuttering which does not show up on Rivatuner. If I cap a game's refresh rate to 60 (or 58 for example), Rivatuner shows a flat frame-time graph, yet the screen stutters when the refresh rate is double of the fps (on VRR mode the OSD fps meter also bounces back and forth between, say 100 and 140Hz).

What really makes me suspect the monitor really is a problem here is the fact if I boot into MacOS (the machine is a hackintosh), when the screen is connected to my motherboard with HDMI and powered via iGPU and I put the screen in 120Hz (VRR naturally doesn't work), I get the same exact stuttering prroblem when viewing 60fps videos. If I switch to 60Hz mode, the stuttering goes away.

So first of all: is LFC suppose to break your frame-pacing? Isn't LFC suppose to kick in at 48fps and not higher? Are you not supposed to be able to view 60, 30 and 24fps content with even frame-pacing on 120Hz screen refresh? Or does this monitor seems busted to you and I should return it (still have about 20 days left).

Secondly: Is there a way for me to disable LFC for the monitor in some way and test how the VRR works if I run with 1:1 ratio for all framerate ranges?

I'm aware of the Nvidia 10-series bug with LFC which gets fixed with cycling 144 and 120Hz back and forth.

I've tried various settings in NVCP, including all Vsync options, different frame-rate limits (I've yet to test say, 69 vs 75fps on a game that supports high refresh rates to see where exactly does LFC kick in).

Any insight into this is greatly appreciated. Thanks in advance!

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Re: Asus VG259Q and stutter with LFC

Post by Chief Blur Buster » 11 Jun 2021, 05:52

I am not sure your specific problem is LFC related.

Video players are often terrible at framepacing. The 60Hz forces a round-off system, so even if a frame is 5ms timed wrong by the video player software, it's rounded off to the correct 60Hz frame. But at 144Hz, refresh cycles are only 6.94ms whereas 60Hz is 16.7ms per Hz. So those software rounding errors starts to be more visible.

Test different players -- VLC, SMPlayer, MPV, MPC-HC, Windows Video Player, Chrome -- you will see some do a better job than others.
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Joined: 11 Jun 2021, 02:37

Re: Asus VG259Q and stutter with LFC

Post by Spedemix » 12 Jun 2021, 04:14

I did some further testing with Freesync and managed to verify it's working as intended: In a game where VRR works properly LFC kicks in at ~60-50fps and stays on until the framerate approaches 70. And at least in my testings the LFC was working properly. Another game that's locked to 60 fps (Genshin Impact) seems to have broken internal framepacing where the Freesync syns into one of the elements on the screen but some other elements run at different frame rate and thus you end up with, say background stuttering. Oddly enough the mismatch goes away when the screen is locked to 60Hz. But that's a problem with the game, not the screen. I've written feedback to the devs about it.

I've yet to figure out though why the screen stutters when playing 60fps videos on 120Hz screen (for the record I'm not attempting to play 30/60fps videos on 144Hz mode, that ofc would stutter due to the mismatch). I'll try different video players to see if that makes a difference (altough it'll be shame to let go of VLC).

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