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.



876 Comments For “G-SYNC 101”

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mspl
Member
mspl

Regarding optimal settings and low latency case, if we use nv’s frame limiter (since the version in which they added fps slider) – we can leave the latency mode on ultra without any issues – as the driver respects the fps slider instead of the earlier pre-determined settings.

Is there any specific reason why the guide suggests to use “on” instead of “ultra” ?

shuaka
Member
shuaka

i posted this question as a reply but i think it will be buried in the comments.
i got this g-sync compatible monitor recently and i would really like to know why borderless windowed is caping my fps even tho i do not have v-sync or any other cap anywhere,
this did not hapen with my other monitor that was not g-sync compatible.(in g-sync setings i do have enable g-sync in windowed also)
and my last question is,would my input latency be higher if i turn off g-sync
(for this specific game)
cause the video from Battle(non)sense states that i would get more lag with g-sync off than with it on.
this game i have to play in borderless… it’s called path of exile

kylmead
Member
kylmead

Hello sorry if this is a double post, I cant find my original. But basically im noticing fps drops and screen flickering when playing fortnite. My goal is to have the smoothest game and least input lag possible. Current running 237 capped fps and 240hz. Gsync on, vsync off, low latency mode off. Is there anything I’m missing for better performance/ smoothness?

NorfPews
Member
NorfPews

Hello. So I’ve been using the optimal guide for G-sync compatibility for most of my games (G-sync on, v-sync on, frame cap 141@144hz) but I’ve noticed that even a very small frame drop of 1 fps causes frame stutter which makes it noticeable in game. I was wondering if that is an intended thing of g-sync compatibility or if this is an issue because my monitor is technically not officially supported for gsync.

GrantVXR
Member
GrantVXR

Hi just wondered if you would be able to help me out. I have g sync enabled using your recommended settings and it works well with no noticeable tearing. I’m playing Call of Duty Warzone and my frames are fairly pinned at the 160fps ive set apart from some parts of the map it drops to 140fps. I’m after the lowest input latency possible so should I unable Nvidias low latency mode? If so which setting should I use? My gpu usage is 97/99%
Many thanks 🙂

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