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.



3525 Comments For “G-SYNC 101”

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BloodyNZ
Member
BloodyNZ

Hey jorimt, thanks for this amazing article and all the research put into it.
My question is if everything present here still applies nowadays with all the new technology and it’s evolution, or anything changed.
I’m rocking a 5060ti but still on a 1080p 144hz display, so I’m trying to optimize it. I play a different range of games, from competitive to single-player. I just want a stable and consistent experience everywhere.

Treeplex
Member
Treeplex

Hello Dear jorimt! I am interested in one question, I will be grateful for the answer. In the game Fall Guys without vertical synchronization limit FPS 300, but with synchronization enabled FPS is equal to 360, what to do in this case?

KasaiRyujin
Member
KasaiRyujin

Hello jorimt, thanks for all the info.

I read almost all the pages of this post, but I’m still not sure what to set in my case.

I have a RTX 4090 + R7 7800X3D. I play on 1440p ~180Hz, so most games run at refresh rate. But I see that the frametime is unstable in some games.

I enabled G-SYNC and set V-Sync to “On”. Also set max framerate to 175 on NVIDIA App.

What should I do with Reflex and Low Latency Mode when I’m hitting refresh rate constantly?
I realized V-Sync has an option called “Fast”, should I use it?

Thanks in advance.

mike-lesnik
Member

Hello jorimt!
For what purpose did Nvidia choose such a significant frame limit for Reflex and LLM Ultra (for example 224 for 240Hz), if you prove that 2-3 frames are enough?

rundown
Member
rundown

Great series, thank you!

Sorry for yet another question about v-sync! 🙂 I do believe that screen tearing occurs with VRR on and v-sync off, but I’m trying to understand on a technical level how it happens with an FPS cap under the max refresh rate? Suppose a 144hz refresh and 140 fps cap.

My understanding is, the display waits in vertical blank until the new frame arrives and immediately scans it out in 1/144 seconds. If the frame limiter is doing its job, a new one shouldn’t arrive until 1/140 seconds after the first one, so the display should be in vblank again.

What am I missing — imperfections in the frame limiter?

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