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.



576 Comments For “G-SYNC 101”

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Zehdah
Member
Zehdah

If I get a 240 Hz monitor, like the BenQ ZOWIE XL2546, should I still be using the method above (Gsync on, Vsync off in game, on in control panel and cap FPS to 237 with RTSS) or should I uncap my framerate with Vsync and Gsync off? The reason I ask is a lot of pros in FPS games such as Apex, Siege, CSGO, seem to do the latter and I can’t understand why, unless G-sync isn’t available on those monitors, but I read that G-sync is available on freesync monitor’s now with 10xx and above cards, am I wrong? Greatly appreciate any input!

DanWensing
Member
DanWensing

Which one has the lowest input lag?
1. Gsync + Vsync + Low Latency Mode at Ultra (no fps limit)
2. Gsync + Vsync + NVC/RTSS fps limit (3fps below Refresh rate)

DanWensing
Member
DanWensing

Hi, I understand that we should use Vsync On when using Gsync. But with the new LG OLED C9, which is gsync compatible, if I have Vsync “ON” I get some microstutter every 10s or so. But if I keep vsync off, the game is 100% smooth (I have the FPS capped at 3fps below the TVs refresh rate). One friend of mine has the same issue with his C9. Do you know why this is happening?

BlackStorm82
Member
BlackStorm82

(Gsync off/Gsync not supported) 144hz 144fps CAP(ingame) (no v-sync) this

144hz 139fps cap(ingame) (no v-sync)
Is it correct to lose input lag than condition?

If I turn off v-sync, is it the same as 139 or 144 cap?
Is a 139fps limit good for 144hz even on a regular monitor? in a v-sync off.
Sorry for the beginner. i love blurbusters

ezidifn
Member
ezidifn

i have a 144hz AMD freesync monitor. How should i get the leasy amount pf input lah? By enabling G sync on nvidia and cap hz at 142/141?

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