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?

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.



172 Comments For “G-SYNC 101”

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Member
king37

Very helpful

Member
besweeet

To confirm, G-SYNC ON + v-sync ON is better than G-SYNC OFF + v-sync ON? My ultimate goal is to eliminate tearing while not introducing input lag, so it seems like the former is the way to go.

Member
hkeep

Thank you for those detailed explanations. My question is why would we enable v-sync if it would never reach the refresh rate cap with the rtss. And also, if for example, I am consistently running the game at a higher refresh rate than my monitor (which is 120hz), what is the point of rtss if it would limit my fps to 2-3 frames below the refresh rate? Shouldn’t I just enable G-sync without a limit which as you said has less input lag than v-sync even when the fps goes over the refresh rate. Which brings to the question of why do we need v-sync at all?

Member
Dragonite

I have the Viewsonic VX2458-C-mhd which is a Freesync monitor. Since my GPU is GTX 1080 i could enable G-sync with the latest drivers. But the problem is that i have brightness flickering (which i read that is a quite frequent occurrence to all adaptive sync technologies). Since i tried to fix it but nothing worked i disabled Freesync/G-sync. So the question is, now that G-sync is off, should i just enable V-sync (NCP) + framelimit for better visual quality and prevent tearing or leave V-sync (NCP) off but still use framelimit?

Member
hyrnos

Hi, thanks for the excellent guide

I want to play games that are capped to 60 ish fps by their game engine, should i enable vsync? (assassin’s creed) I ofc want to enable gsync

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