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.



3006 Comments For “G-SYNC 101”

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dandyjr
Member
dandyjr

Hey Jorimt, I have a question regarding the issue of avoiding the G-Sync ceiling.

I recently purchased a 280Hz Freesync monitor (it’s not official G-Sync Compatible but after testing in multiple games, it seems to mirror my 144Hz officially G-Sync Compatible monitor in accuracy) and I’ve noticed an issue that has happened on previous monitors I’ve owned as well.

This monitor doesn’t have an OSD that I can have toggled on at all times so I had to manually open the menu to check each time but I’ve noticed that there are multiple moments where the refresh rate will read as 280Hz instead of whatever framerate the game is reading as at the time.

For example, I tried with in-game and external limiters, I can cap the frames at 240fps and the game will read as 240fps but when I open the menu of the monitor, it reads as 280Hz for that moment (causing me to believe that G-Sync has disabled in that moment and Vsync has toggled on). Then I’ll close the menu and reopen it and then the refresh rate will read as some variation under the 280Hz ceiling. That lets me know that G-Sync does engage, but there are moments where it’s not engaging even when it should.

I tested this in multiple games with multiple forms of framerate caps and noticed the same trend. The closer I capped to 280Hz, the more times I would see 280Hz in the monitor. The only way to stop it from happening was to cap the framerate far below the ceiling. Capping at 277fps, for example, in RTSS caused the 280Hz readout to never change at all (which would indicate that G-Sync was not engaging) which caused me a lot of frustration.

I would think that it’s possibly due to the monitor not being offically G-Sync Compatible but the same issue would happen with my 144Hz monitor as well (with lower framerates of course because the ceiling is lower) and that monitor had an OSD that I could leave toggled on. I would see the numbers rapidly change and by watching very closely, you could see the 144Hz flash multiple times within the mixture.

Am I overthinking this or are the monitors actually reading correctly and G-Sync is disengaging and re-engaging constantly even with framerate caps below the ceiling?

It’s sad to think that the 280Hz ceiling is useless because framerates need to be capped far below the ceiling even with external limiters that appear to be perfect in execution.

TkoSeven
Member
TkoSeven

Thanks for the wonderful article.

2 questions!

Adjust desktop size and position section,
“Perform scaling on: Display or GPU” (also override the scaling mode set by games and programs)
does it matter in terms of how g-sync monitor
interacts with GPU?

2nd question on “Max frame rate” on Nvidia settings,
if a game was designed to be locked at 60fps, like Tekken 8,
Nvidia panel set to 58 fps, does it work by limiting frame data transferred to display even though
the logic of the game (application) actually went through generating data for 60 frames?
or
does it actually limit the game to only generate 58 frames?

thank you in advance.

eeayree
Member
eeayree

Hi jorimt. I myself am from another country and therefore I hope that the translator will do his job correctly. Now I’m playing Metro 2033 and this game can produce from 80 to 120 fps on my system and at the same time the GPU is not working at full capacity. It works within 85 percent. Your tuning guide states that it is best to enable low latency mode in cases where the frame rate does not always reach or exceed the refresh rate. Am I doing the right thing if I leave low latency mode on if the video card is not loading at 99%? And at what percentage values ​​does the delay appear exclusively at 99%? On 95, 96, 97 will everything work with minimal delays?

SovonHalder
Member
SovonHalder

HI jorimt, I can’t thank you enough for writing this article. I read pages 1 through 15 multiple times to understand as much as I cound and i’t’s incredibly useful for folks like me who are new to PC gaming. Just wanted to acknowledge that adn say many thanks brother.

So I set up things for my 144hz 32GR93U exactly as you described: In nvcp Gsync+Vsync+Low latency ultra and the in game Vsync, double or triple buffering off and fullscreen on. I have 2 questions basically.

1. In most games I’ve tried so far like alan wake 2, god of war, stray the fps is capped automatically to 138 as it should but in red dead online (vulkan) it maxes out at 144. I use rtss to set it custom 138 but the question remains. Why doesn’t it happen automatically?

2. The new nvidia app reports an Average PC Latency in their overlay. For me above 60ms with mouse and controller feels sluggish whereas when it’s below 30ms the game feels much more responsive. I want to implement that on my RTSS stat overlay. (I find rtss overlay more robust and feature rich and I can see frametime grap and nvidia overlay is finicky and slow.) Could you share some insight as to how they are calculating that number?

Ezi
Member
Ezi

I have a question, so i did the settings you suggested and my gpu usage went from 99% usage to hovering around 70-88ish. Is this normal? Cause if i were to default everything back, the usage would go back to 99%

these are the settings i have in NCP:
– vsync on in NCP, off ingame
– set fps limiter -3
– gsync enabled – full screen
– LLM set to ultra since ingame doesnt have a limiter

my pc spec is:
– 4080 super FE
– 7800x3D
– M32U 4k 144hz monitor

wpDiscuz