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.



90 Comments For “G-SYNC 101”

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pervyjutsu
Member
pervyjutsu

Should “Reduce Buffering” option in Overwatch be enabled or disabled? Many competitive/pro players suggest having reduce buffering on to get higher framerate and reduced input lag but would having this option on have a negative effect on G-SYNC?

Also I recently upgraded my system to a i7-8700k and 1080ti. I usually sit at a steady 300fps on Overwatch now and use a 240hz monitor (Asus PG258Q). Would G-SYNC be worth using in this case?

shashank066
Member
shashank066

Excellent article. Just like other on Blur Busters. It was such detailed that, I had to read it twice to understand perfectly. Thanks for this.

bcbuse
Member
bcbuse

First, this is the best Gsync/Vsync information on the internet. I appreciate the effort you put into this, well done.

I read a comment you posted somewhere that ‘technically’ the absolute least input lag would be with Gsync Off + Vsync Off + Framerate upcapped(getting at least 2x the monitor refresh rate). Can you approximate how much less input lag that would be versus Gsync On + Vsync On(NVCP) + Framerate capped 2 below monitor refresh rate?

daniel8747
Member
daniel8747

to clarify: with fps capped 2-3 fps below monitor refresh rate, do i still need to have v-sync enabled?

Abiak
Member
Abiak
jorimt please answer. 1) NVIDIA Control Panel G-Sync: Full Screen vs. Windowed and Full Screen, which one should I use for gaming? 2) Does just “full screen” work on windowed borderless? 3) Preferred refresh rate “Highest Available” or “Application controlled”? 4) Does “Highest Available” work on windowed borderless? 5) From what I understood, for a 144Hz monitor, the best options are gync + vsync on (NVCP) + in-game vsync off and frame limited to 142 fps. However I don’t get why you need vsync, why gsync + frame limiter is not enough? 6) If the game has no fps-limiter, you… Read more »
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