G-SYNC 101: G-SYNC vs. V-SYNC w/FPS Limit


So Close, Yet So Far Apart

On the subject of single, tear-free frame delivery, how does standalone double buffer V-SYNC compare to G-SYNC with the same framerate limit?

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

As the results show, but for 60Hz (remember, a “frame” of delay is relative to the refresh rate), the numbers are relatively close. So what’s so great about G-SYNC’s ability to adjust the refresh rate to the framerate, if the majority of added input latency with V-SYNC can be eliminated with a simple FPS limit? Well, as the title of this section hints, it’s not quite that cut and dry…

While it’s common knowledge that limiting the FPS below the refresh rate with V-SYNC prevents the over-queuing of frames, and thus majority of added input latency, it isn’t without its downsides.

Unlike G-SYNC, V-SYNC must attempt to time frame delivery to the fixed refresh rate of the display. If it misses a single one of these delivery windows below the maximum refresh rate, the current frame must repeat once until the next frame can be displayed, locking the framerate to half the refresh rate, causing stutter. If the framerate exceeds the maximum refresh rate, the display can’t keep up with frame output, as rendered frames over-queue in both buffers, and appearance of frames is delayed yet again, which is why an FPS limit is needed to prevent this in the first place.

When an FPS limit is set with V-SYNC, the times it can deliver frames per second is shrunk. If, for instance, the FPS limiter is set to 59 fps on a 60Hz display, instead of 60 frames being delivered per second, only 59 will be delivered, which means roughly every second a frame will repeat.

As the numbers show, while G-SYNC and V-SYNC averages are close over a period of frames, evident by the maximums, it eventually adds up, causing 1/2 to 1 frame of accumulative delay, as well as recurring stutter due to repeated frames. This is why it is recommended to set a V-SYNC FPS limit mere decimals below the refresh rate via external programs such as RTSS.

That said, an FPS limit is superior to no FPS limit with double buffer V-SYNC, so long as the framerate can be sustained above the refresh rate at all times. However, G-SYNC’s ability to adjust the refresh rate to the framerate eliminates this issue entirely, and, yet again, beats V-SYNC hands down.



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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