G-SYNC 101: G-SYNC vs. V-SYNC OFF


Beyond the Limits of the Scanout

It’s already been established that single, tear-free frame delivery is limited by the scanout, and V-SYNC OFF can defeat it by allowing more than one frame scan per scanout. That said, how much of an input lag advantage can be had over G-SYNC, and how high must the framerate be sustained above the refresh rate to diminish tearing artifacts and justify the difference?

Blur Buster's G-SYNC 101: Input Latency & Optimal Settings
Blur Buster's G-SYNC 101: Input Latency & Optimal Settings
Blur Buster's G-SYNC 101: Input Latency & Optimal Settings
Blur Buster's G-SYNC 101: Input Latency & Optimal Settings
Blur Buster's G-SYNC 101: Input Latency & Optimal Settings
Blur Buster's G-SYNC 101: Input Latency & Optimal Settings

Quite high. Counting first on-screen reactions, V-SYNC OFF already has a slight input lag advantage (up to a 1/2 frame) over G-SYNC at the same framerate, especially the lower the refresh rate, but it actually takes a considerable increase in framerate above the given refresh rate to widen the gap to significant levels. And while the reductions may look significant in bar chart form, even with framerates in excess of 3x the refresh rate, and when measured at middle screen (crosshair-level) only, V-SYNC OFF actually has a limited advantage over G-SYNC in practice, and most of it is in areas that one could argue, for the average player, are comparatively useless when something such as a viewmodel’s wrist is updated 1-3ms faster with V-SYNC OFF.

This is where the refresh rate/sustained framerate ratio factors in:

Blur Buster's G-SYNC 101: Input Latency & Optimal Settings
Blur Buster's G-SYNC 101: Input Latency & Optimal Settings
Blur Buster's G-SYNC 101: Input Latency & Optimal Settings

As shown in the above diagrams, the true advantage comes when V-SYNC OFF can allow not just two, but multiple frame scans in a single scanout. Unlike syncing solutions, with V-SYNC OFF, the frametime is not paced to the scanout, and a frame will begin scanning in as soon as it’s rendered, regardless whether the previous frame scan is still in progress. At 144Hz with 1000 FPS, for instance, this means with a sustained frametime of 1ms, the display updates nearly 7 times in a single scanout.

In fact, at 240Hz, first on-screen reactions became so fast at 1000 FPS and 0 FPS, that the inherit delay in my mouse and display became the bottleneck for minimum measurements.

So, for competitive players, V-SYNC OFF still reigns supreme in the input lag realm, especially if sustained framerates can exceed the refresh rate by 5x or more. However, while at higher refresh rates, visible tearing artifacts are all but eliminated at these ratios, it can instead manifest as microstutter, and thus, even at its best, V-SYNC OFF still can’t match the consistency of G-SYNC frame delivery.



220 Comments For “G-SYNC 101”

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gen36
Member
gen36

Hi, I have a question about limiting frame rate at (refresh rate – 3).

My understanding is that if FPS > refresh rate, GSYNC defaults to VSYNC behavior (if VSYNC is enabled in Nvidia CP), which can result in additional input lag.

But I have some confusion on this. Example scenario:

– 144 Hz monitor.
– I’m playing an undemanding game, VSYNC OFF, and get 200 FPS.
– I turn on GSYNC + VSYNC, and get 144 FPS.
– With GSYNC + VSYNC on, is it defaulting to VSYNC ON behavior? Frame rate is not exceeding refresh rate but *would have* if vsync was off.

(My confusion is coming from the section in the FAQ saying if your frame rate exceeds refresh rate, to cap at a value lower than refresh rate, but if vsync is on, FPS doesn’t exceed refresh rate anyway)

Silver3
Member
Silver3

I was wondering if you could explain me a very persistent Frametime-Spiking-relating issue I’ve got recently with the console-emulator Cemu that I am tearing my hair out about at this time.

[… original comment modified here for length; view below comment reply for pertinent details w/follow-up…]

Sorry btw for that wall of text, but I am quite at my wit’s end by now on my way comprehending other/similar builds’ success although they probably don’t care half of that, pc-related, the way I do and I seemingly checked all of your mentioned points possibly causing frametime-spikes
and will continue with the hardware-part tomorrow.
If you have any suggestion that merely could hint in a direction I overlooked, PLEASE let me know.

Thank you for reading.

Skwuruhl
Member
Skwuruhl

On the topic of FPS limiters: Two tests have been done somewhat recently that found that RTSS provides more consistent frame times than in-game limiters do (at the expense of 1 frame of input lag)
https://youtu.be/xsXFUVYPIx4
https://www.reddit.com/r/Competitiveoverwatch/comments/9vcxz5/rtss_vs_ingame_fps_cap_or_frame_limit/
What’s your take on these?

rpate124
Member
rpate124

What value should the frame time limit be set to in rtss?

GITS_2501
Member
GITS_2501

Amazingly detailed, thanks for the guide. Is there a difference between having V-SYNC: ON versus VSYNC: Fast?

Thanks heaps.

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