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.



2042 Comments For “G-SYNC 101”

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zikalol
Member
zikalol

Hi, i have a dell freesync monitor. The issue is when i enable Gsync the monitor turns off mid-game. can’t figure out what is causing this issue. thank you

Zanity
Member
Zanity

Hi, quick question, why do we still need to set 3 fps lower if we use nvidia ultra low latency mode ? which automatically force caps the frame rate lower already. thanks

Zehdah
Member
Zehdah

Hi Jorimt. I’m just wondering if the “variable refresh rate” option in Windows 10 graphics settings should be enabled or disabled or if it makes no difference? I use a Gsync monitor.

domfak
Member
domfak

Hello,

Want to thank you for all the info in this page.
Also I have couple of questions:

I got RTX 3080 + 165hz monitor, I am having those tearing lines on my low side of display if I play with GSync + uncapped fps. Sometimes it feels like stuttering. So I decided to try your method.
But where are some issues in game COD: Warzone:

1) GSync On + Vsync ON + LLM (Ultra) + Reflex On + Boost – caps my FPS in game at 60. Why?

2) GSync On + Vsync FAST + LLM Ultra + Reflex On+ Boost – I can cap myself at 161fps as you proposed. And FPS are dipping from 140 to 161. Also with thise method I found that blur line in the bottom of the screen still exist.

What is difference between VSync ON / VSync Fast?
Will I get more input delay in this case?
Also can I feel that option with Gsync + Vsync has more input delay on my mouse or it is only placebo?

Thanks for an answer.

majkool
Member
majkool

1. So with 390Hz monitor input lag with GSYNC + VSYNC and 386fps game limitter is nearly the same like with GSYNC/VSYNC off and fps_max 0 in CSGO.
2. I know that with 240Hz monitor there is a few ms delay with these options but I think it’s still better to accustom to it and play on a pro level?

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