1/2 Refresh Rate - inconsistent input lag?

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Finnen
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Joined: 04 Nov 2019, 16:32

1/2 Refresh Rate - inconsistent input lag?

Post by Finnen » 04 Nov 2019, 16:49

Sometimes, when I can't maintain stable 60 FPS in games, I tend to lock them at 30 FPS for more consistent experience. I play mostly RPGs / TPP games, so it's not really a problem for me. I vastly prefer "flat-line" 30 FPS than fluctuating 40-50. To do that and minimize the input lag, I use the following method:

- disable in-game VSync
- force "1/2 Refresh Rate" standard VSync through NVIDIA Inspector
- set the maximum pre-rendered to 1
- lock the frame rate to 0.01 FPS below the half of my refresh rate in RTSS (59.99Hz / 2 = 29.995Hz, so I lock to 29.98)

This trick always worked fine. It gave me very consistent 30 FPS with heavily minimized input lag (though, in my opinion, still higher than some console games like Horizon, which is quite bizzare).

Sadly, this "trick" is hard to pull recently. I am using Windows 10 (1903). I started to notice that input lag is not as low as it used to be when doing the above procedure. What's most important, the input lag became inconsistent. I can actually feel that it's changing while playing the game - sometimes it's higher, sometimes it's lower.

The most bizzare thing, however, is that when I launch the game the input lag is a bit high. Then I press ALT+TAB and go back to the game. Suddenly, input lag is much lower (as it used to be long ago when I used this trick before), it works fine for several seconds, and then it rises again and the game clearly feels less responsive. The same "switch" of latency can happen even after opening/closing in-game menus or, for example, going through the loading screen when reloading save game or switching zones.

Has anyone encountered such phenomenon? It's almost as if the RTSS was losing focus on the game or something? Though not completely, because when I completely disable RTSS or set the framerate limiter to 0, I can feel even higher input lag. I tried disabling full screen optimizations in Windows 10, game bar, setting the compatibility to Windows 7 (to disable all kinds of enhancements Windows 10 might be adding), enabling/disabling HPET in BIOS, changing maximum pre-rendered frames, setting the latest Ultra Low Latency Mode. Nope, nothing, absolutely the same results in all cases.

Tested on games on Origin (for example, Kingdoms of Amalur at 4K res) and from Xbox Game Pass (The Outer Worlds) and Steam (for example, Skyrim Special Edition). Can install more games and test more, if needed.

Spec: i5-4440, GTX 970, 16GB RAM, latest NVIDIA Drivers (fairly fresh installation of Windows 10, the same thing happened in two previous NVIDIA driver versions)

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RealNC
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Re: 1/2 Refresh Rate - inconsistent input lag?

Post by RealNC » 07 Nov 2019, 09:01

Did you test for your actual refresh rate? Most monitors are not 60.0Hz. They're somewhere near 59.94 so you'd need to cap to 29.96FPS. Test here:

https://www.testufo.com/refreshrate

Make sure your browser has hardware acceleration enabled.

Also, you might want to try RTSS scanline sync x/2. If that works for your game, it provides the lower input lag.
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