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.



662 Comments For “G-SYNC 101”

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Sort by:   newest | oldest | most liked
BlackStorm82
Member
BlackStorm82

HI
“fixed refresh rate”
Do you have information about?

Is it correct that G-Sync does not work when I use this?
In-game [frame limit release mode]
When it comes to monitor technology G-Sync, 100-600 FPS was also released.

[fixed refresh rate]
When I activated the League of Legends with this function, 300FPS was fixed.

rocet
Member
rocet

Hi, maybe i’m misreading or misunderstanding the graphs/article but there is no downside to just using G-Sync ON + V-Sync OFF + No fps limit?

G-sync would activate when below 144fps and then ‘de-activate’ above 144? Causing no input lag?

Zehdah
Member
Zehdah

I know that for the lowest possible input lag, you want to find the highest framerate your system can achieve an average of 95-99% of the time without maxing your GPU usage and cap your framerate there with an in game limiter, but what do I do to achieve that in a game like Warzone where my FPS can be as low as 140 in big open areas or as high as 240 when inside a building or small area?

My CPU and GPU usage always seem to be very high at 85-97%. I have an i7 9700k and 1080ti, playing on a 240hz monitor. The game seems to be poorly optimized so I’m struggling to decide what to do.

fanatycme
Member
fanatycme

When I play DOTA 2, my fps is all the time at ~117 because i capped it, but at the end of the game, when match finishes the base gets destroyed and i get a FPS DROP from ~117 fps to 80-90 fps and my game STUTTERS, is it normal? i am playing with g sync, vsync and fps cap, i thought gsync is supposed to GET RID of stutter or I do SOMETHING WRONG?? during the rest of the game everything seems ok

i am using:
-nvcp: gsync on fullscreen, highest refresh rate, vsync let 3d app decide
-dota2: vsync on, fps max 117 (120hz monitor), highest video settings
-latest drivers, gtx 1070, monitor aw3418dw

AnonymousH
Member
AnonymousH

I typically prioritize input latency and thus normally run with G-SYNC but without any framerate limit or V-Sync, which causes some tearing at high framerates. I initially thought that Fast Sync eliminates tearing but introduces some microstutter, and that was all, making it a viable option in combination with G-SYNC, and the rest depends on preference (with G-SYNC: none = tearing, V-Sync + framerate limit = higher latency, Fast Sync = microstutter). However, if I’m reading this correctly, even G-SYNC + Fast Sync without a frame limit isn’t recommended because it limits the framerate to something lower than the monitor refresh rate, or runs starting at that slightly lower framerate?

wpDiscuz