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.



1655 Comments For “G-SYNC 101”

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Linkaran
Member
Linkaran

It’s a great article, I understood a lot of things

However, recently the Mass Effect Legendary Edition game was released, it imposes different framerate limitation ranges like 30/60/120/144 and 240.

This makes it impossible to limit the FPS to 117 for a 120hz screen for example via the nvidia control panel
Cannot disable this option in the game, forced to play 30/60/120/144 or 240 fps or nothing

What do you recommend in this case?

Enable 120 FPS limitation in Mass Effect + Vsync game with nvidia control panel?

or the limit of 120 FPS in the game + vsync in the game?

this game is a special case that I find interesting concerning the GSYNC + VSYNC because it forces its framerate limitation in the game

askobilv
Member
askobilv

A lower fps limit would rob frames

What if I want to reduce load on my GPU and CPU by capping to lower values like somewhere between 60-90 (on 144hz monitor)

Could that work or I will experience bad implications?

Jimmy
Member
Jimmy

Hi, thank you for the great articles you guys are amazing.
I have one quick question. I’ve recently bought a G-SYNC monitor 144hz and its capable of 180hz OC. The game that I play gives me around 160-170 fps. Do you recommend capping my fps @ 141 or OC the monitor and let the G-SYNC do its job while capping @ 177 ? My main goal is lower input lag with the highest fps.

18koko
Member
18koko

Hi I just want to ask if I enable low latency mode in nvidia control panel and also enble ingame low latency mode (valorant nvidia reflex on+boost) will it conflict with each another? Do I enable both or no?

christofin
Member
christofin

Hello, thank you for the wonderful article. I’ve been using a g-sync compatible monitor for a long time and have always left g-sync on, vsync on, and a framerate cap in the Nvidia control panel at 156fps with a 160hz monitor.

I think as time has gone on I’ve become more sensitive to noticing microstuttering in games. For example PUBG is an absolute stutterfest and it’s something I used to not notice. Likewise with games with awful frame pacing issues in general like Dark Souls 3. I’ve always tried to stick to games that have very smooth frametimes, like Overwatch. But even now with the reflex patch, I’ve seen a few frametime spikes here and there in Overwatch and I have to admit that it does bother me.

My question to you is this: is there something I can do system wide to reduce frame time spikes? Would turning off vsync help? I saw in the article in the stuttering section, you mentioned that if the game has a pause, no settings can fix that, but are there any settings that could mitigate how noticeable it is?

I used to try to just throw money at the hardware to mitigate stuttering. I’ve upgraded my ram and power supply, for example. Right now I have a 9900k with a mild overclock and a 3090 founders edition running at stock. I do aggressively monitor what tasks I let run in the background and I generally keep software closed while I’m playing games. Is there anything else I can do to help reduce stuttering in various games?

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