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.



273 Comments For “G-SYNC 101”

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Phroster
Member
Phroster

Why is it, that in most games, borderless fullscreen + gsync, gives worse results then exclusive full screen mode? (uneven frametimes, micro stutters)
Using a frame limiter to set the framerate -3 below the refresh rate makes it even worse when using borderless fullscreen.

I did find that G-sync + Fast sync + borderless fullscreen seems to give better results in some games. Still limiting the frame rate in borderless fullscreen, introduces microstutters.

Why is borderless fullscreen so unreliable with gsync enabled?

jdawg
Member
jdawg

Hey, so I didn’t know about turning on V-sync in NVCP only, but before I did that I was getting the occasional stutter even though the action on screen wasn’t that intense. I have RTSS showing a graph of FPS and I notice there are several little dips happening every second. The game moves smooth but then I get the stutter occasionally. I’ve closed everything unnecessary but maybe there’s more to close…not sure what other processes I can close in Windows 10 and I haven’t done any optimizations like in Windows 7.

Fast forward to setting it up as recommended here (141 FPS limit in game for my 144Hz monitor, G-sync on, V-sync ON in NVCP only, V-sync OFF in-game) and I noticed that the dips on the graph are even deeper…however I haven’t seen a stutter yet and the game plays very smooth with no lag. Any explanation for those dips in the graph though?

metalpizza123
Member
metalpizza123

Hi hi, Just a quick heads up for users with several displays of varying refresh rates. Windows will sometimes only report the lowest refresh rate monitor as the system-wide V-Sync target. After testing on driver ver 436.02, with 3 different monitors, here are my findings. I testeed with 3 games, all had similar behaviour. I used the recommended settings as per the guide.
NVCP V-sync ON
Gsync Enabled
Ingame FPS Limiter or RTSS used
Ingame Vsync/buffering disabled

Main monitor :G-Sync, 144hz.
Second Monitor 60 Hz
In game Framerate 60~

Main monitor :G-Sync, 144hz
Second monitor 75 Hz
In game Framerate 75~

Main monitor G-sync,144hz
Second monitor, 60hz
third monitor, 75hz
In game framerate 60~

Only main monitor: G-Sync 144hz
In game frame rate 140~

There’s probably a way to disable this, but for now I’ve resorted to just unplugging my other monitors. Just a note for any multi monitor users. I wish I could test more, but I just wanna play games.

kucki
Member
kucki

Should we use the “Low Latency Mode” On or Ultra with G-Sync?

Chief Blur Buster
Admin

Possibly beneficial for uncapped GSYNC + VSYNC ON. Will need to be tested.

This will reduce lag differential of below-Hz (GSYNC behavior) versus match-Hz (VSYNC ON behavior).

Creakffm
Member
Creakffm

Hello Guys, really Intresting Article/Guide but i wanna know something from you.

i Playing Games since 20 Years i know in Old Times with 60 HZ Monitors i play Competitive Games with VSYNC off to get most FPS ingame.

So back to 2019.

Im Using a Nvidia Geforce 1080 TI and my Monitor is 240 HZ DELL Alienware AW2518HF with GSYNC on Displayport Cable.

i wanna Optimizing all to Play Competitive. Actual i play with Ingame Fortnite Framerate Limit 240 HZ because see this by a lot of People.

When i wanna get less Inputlag i set in Nvidia Inspector Framerate Limiter to 245,244 ( more FPS than HZ or less and than which one is best? )

thanks for Answering

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