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.



251 Comments For “G-SYNC 101”

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Savatgy
Member
Savatgy

NO matter how I configure G Sync, it appears to cause input lag in Overwatch.

Chief Blur Buster
Admin

Which monitor model? And G-SYNC native or G-SYNC compatible (FreeSync)?

Karker
Member
Karker

so functionally and properly setup, gsync and quite possibly gsync-compatible* should have lower input lag than even an uncapped frame rate?

if this is the case, why arent competitive gamers doing this?

ivandudude
Member
ivandudude

should i cap it to 141 if i have a 144hz monitor with v sync on or off? also i dont have g sync but im looking to get the less input lag. this is for fortnite and this game called smite.

bioinfinite121818
Member
bioinfinite121818

Hi, I was wondering I recently bought a g sync 240hzmonitor and I have g sync and nvidia v sync on, should I lower the refresh rate of my monitor 237 or is okay if I can keep it at 240?

rayjays1986
Member
rayjays1986

Was wondering, do you have any advice on State of Decay 2? I seem to be having major stutter/lag issues with that game and G-Sync. It’s hard to explain, it’s almost as if there’s some sort of asset loading going on while I’m driving especially, and it looks quite laggy/stuttery. I have seen numerous others talk of this, and numerous others who say it runs smooth as butter. I change over to fixed refresh and vsync, and it seems to help a little, but it’s not totally gone. BUT, using fixed refresh w/ fast sync, it almost (not quite but almost) eliminates the effect, with the lag much less apparent. I experimented a bit and G-sync plus fast sync seems to help too, though here it says not to do that. I wouldn’t think of doing that in anything else, I just seen several posts that it had something to do w/ that game/engine in particular w/ G-sync and laggy/stuttery moments on occasion. Did you (or anyone else here) happen to experience any of this with State of Decay 2? If so, anyone know how to fix it? I actually really enjoy the game, but that lag is incredibly annoying for me (seems to happen most when I’m driving). Thanks in advance for any answers!

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