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.



1917 Comments For “G-SYNC 101”

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vizionblind
Member
vizionblind

Hello,

I have a 165 HZ monitor (the Gigabyte M32Q) and I mostly play FPS games and Open World Games. Just trying to understand if I need to do anything besides enablge gsync and vsync on in NVCP.
https://www.amazon.com/dp/B0968QT6SS?ref=ppx_yo2_dt_b_product_details&th=1

roro13200
Member
roro13200

Hello
I have a 165hz gsync compatible screen, and an rtx 2060.
I mainly play fighting games which are capped at 60fps.
what are the parameters that you advise?
thank you and sorry for my english!

Dan_G_303
Member
Dan_G_303

Hi Jorim, thanks for this guide. I had a question – I have a 144 Hz G-sync compatible screen (AOC AG241QX) but prefer capping to 60 fps, as for some games this is near the max fps my PC can produce, and I prefer a consistent refresh rate no matter the content, rather than running some games at 60 fps and less demanding games at higher fps (this also keeps me from spending too much money on a high end GPU as I’m not always chasing 144 fps !). I have refresh rate in Windows display settings set to 60 Hz too so that just normal desktop use is also consistent.

As far as I understand, for exclusive fullscreen games the Windows refresh rate setting is overwritten and the screen’s max refresh rate is used instead (144 Hz in my case) so that any fps cap ~3fps or more under the screen’s refresh rate will do the job of keeping the fps within the G-SYNC range (for my screen this would be a fps cap anywhere between 141-30 fps and I prefer to set it to 60fps).

However – for games that don’t have proper exclusive fullscreen (or those where borderless fullscreen is more convenient) the refresh rate seems to stick to the Windows display setting (60 Hz in my case). For these games should the fps limit be 57fps, or would 60fps still work?

Also for information – on my screen there appears to not be any built in hardware setting to set the refresh rate (i.e. in the screen’s OSD) – otherwise that would solve it.

Thanks.

SkaKunK
Member
SkaKunK

Hi jorimt. I am Spanish. I hope you understand me well.

I recently bought a LG C1 OLED 120Hz Gsync compatible TV and a nvidia 3060ti. My problem is that I have micro stuttering and it seems strange to me because while the Afterburner statistics say that I am playing for example at a constant 60fps 16.6, in the GSYNC menu of the TV I can see that the fps vary a lot and all the time; 63,70,57 , 52.

In some games they vary less than in others. I’m confused. I thought they would vary from 59 to 60 at most. How can it be that on the PC it tells me a constant 60fps 16.6ms and on the TV it doesn’t? I just activate vertical sync in the game (without GSYNC) and RTSS limiter at 60fps and I feel it better and smooth.

What could be the problem?. Thanks for advance 🙂

gsyncnoob2
Member
gsyncnoob2

Hello @jorimit,

Thanks for putting those together really helpful!

I used G+VSYNC in NVCP and in game(world of tanks) fps_max @141, however I noticed that the fps is staying at 124-125hz on my 144hz monitor, if I change fps_max to 144, it stables at 143-144hz, I am kinda new to gsync, but is it the expected behavior? I thought this setup should stay at 144hz.

Thanks!

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