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


At the Mercy of the Scanout

Now that the FPS limit required for G-SYNC to avoid V-SYNC-level input lag has been established, how does G-SYNC + V-SYNC and G-SYNC + V-SYNC “Off” compare to V-SYNC OFF at the same framerate?

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

The results show a consistent difference between the three methods across most refresh rates (240Hz is nearly equalized in any scenario), with V-SYNC OFF (G-SYNC + V-SYNC “Off,” to a lesser degree) appearing to have a slight edge over G-SYNC + V-SYNC. Why? The answer is tearing…

With any vertical synchronization method, the delivery speed of a single, tear-free frame (barring unrelated frame delay caused by many other factors) is ultimately limited by the scanout. As mentioned in G-SYNC 101: Range, The “scanout” is the total time it takes a single frame to be physically drawn, pixel by pixel, left to right, top to bottom on-screen.

With a fixed refresh rate display, both the refresh rate and scanout remain fixed at their maximum, regardless of framerate. With G-SYNC, the refresh rate is matched to the framerate, and while the scanout speed remains fixed, the refresh rate controls how many times the scanout is repeated per second (60 times at 60 FPS/60Hz, 45 times at 45 fps/45Hz, etc), along with the duration of the vertical blanking interval (the span between the previous and next frame scan), where G-SYNC calculates and performs all overdrive and synchronization adjustments from frame to frame.

The scanout speed itself, both on a fixed refresh rate and variable refresh rate display, is dictated by the current maximum refresh rate of the display:

Blur Buster's G-SYNC 101: Scanout Speed DiagramAs the diagram shows, the higher the refresh rate of the display, the faster the scanout speed becomes. This also explains why V-SYNC OFF’s input lag advantage, especially at the same framerate as G-SYNC, is reduced as the refresh rate increases; single frame delivery becomes faster, and V-SYNC OFF has less of an opportunity to defeat the scanout.

V-SYNC OFF can defeat the scanout by starting the scan of the next frame(s) within the previous frame’s scanout anywhere on screen, and at any given time:

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

This results in simultaneous delivery of more than one frame scan in a single scanout (tearing), but also a reduction in input lag; the amount of which is dictated by the positioning and number of tearline(s), which is further dictated by the refresh rate/sustained framerate ratio (more on this later).

As noted in G-SYNC 101: Range, G-SYNC + VSYNC “Off” (a.k.a. Adaptive G-SYNC) can have a slight input lag reduction over G-SYNC + V-SYNC as well, since it will opt for tearing instead of aligning the next frame scan to the next scanout when sudden frametime variances occur.

To eliminate tearing, G-SYNC + VSYNC is limited to completing a single frame scan per scanout, and it must follow the scanout from top to bottom, without exception. On paper, this can give the impression that G-SYNC + V-SYNC has an increase in latency over the other two methods. However, the delivery of a single, complete frame with G-SYNC + V-SYNC is actually the lowest possible, or neutral speed, and the advantage seen with V-SYNC OFF is the negative reduction in delivery speed, due to its ability to defeat the scanout.

Bottom-line, within its range, G-SYNC + V-SYNC delivers single, tear-free frames to the display the fastest the scanout allows; any faster, and tearing would be introduced.



1304 Comments For “G-SYNC 101”

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Zrex
Member
Zrex

Hi I just recently bought the new Asus PG259QN 360hz Monitor just wanted to get a little bit of information on what’s best for a competitive settings/setup.

– Should I use g-sync with the optimal settings or Fixed refresh uncapped ?

– Game I usually play is siege and its uses DX11 & vulkan api, should I run DX11 api with LLM on/ultra or vulkan with LLM off ?

Also is it fine to use display scaling or GPU Scaling in nvcp does it matter in g-sync fixed refresh rate settings ?

– I also use 2 monitors one is at 60hz can go to 144hz and one is my main at 360hz will that conflict with anything including stutters etc?

nevo2323
Member
nevo2323

Hi, I understand that gsync barely adds lag compare to only vsync and offer a tearless experience but how does it compare to the fixed refresh settings? which one gives the lowest input lag? (At frame rates lower than refresh rate and higher than it, each case to its own of course)
Thanks!

hramulka
Member
hramulka

Thank You so much for being there and helping users!!!

mct1980
Member
mct1980

Nice bit of info here. Cheers! Is it possible to avoid screen flickering when fps drops below 30 when the gpu usage is low? Like forcing it to run at minimum 30 fps even if the application doesn’t want it to?

BlackStorm82
Member
BlackStorm82

Hello, God of Knowledge.
G-SYNC ULTIMATE VS G-SYNC VS G-SYNC COMPATIBLE

Is G-SYNC ULTIMATE or G-SYNC more advantageous in Inputlag than G-Sync compatibility?

Can you say that the compatibility between G-Sync and G-Sync differs in the smoothness of the screen?

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