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.



2981 Comments For “G-SYNC 101”

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wrdh
Member
wrdh

Hey! I hope you can help me. My PC setup includes an RTX 4070 (ASUS TUF OC), i5-14600KF, and an ASUS TUF VG27AQA1A monitor (supports FreeSync and is G-Sync compatible). My problem is that games don’t feel smooth, even though the FPS shows 144-170 (currently using DisplayPort, 165Hz), with FreeSync turned on and G-Sync for fullscreen games also turned on. When I use G-Sync, my monitor flickers (only in fullscreen games).

Here’s a summary of the settings:

V-Sync is on
LLM – Ultra
G-Sync is on
I’ve had this problem since I bought my new PC a month ago. I don’t think games should look like this, so I suspect a driver update might help when a new version comes out.

Thank you for your time!

kizx
Member
kizx

hey πŸ˜€ , quick question was gives the less latency between RTTS to cap frame or NVCP? thanks

jtcuth48
Member
jtcuth48

Hey Jorimt! Apologies if this has been asked before.

If the game does not have customizable vsync settings and it’s forced on (mainly looking at the From Software games here), is enabling vsync in the control panel still optimal? Will in-game vsync on and the control panel vsync conflict and create any adverse effects? Should I let the 3D application decide in this case?

Thanks!

kizx
Member
kizx

Hello Jorimt, I have a question for the longest time I have like weird feels bad/ stuttering /frame drops idk how to call it in my league of legends game due to dual monitor my primary being 140 hz and my secondary being not the same 60 hz. After reading your post about imput-lag I managed to isolate to problem by going full screen with G-sync-V-sync on in the nvidia control panel but then I keep reading you also mention that if the game we are playing doesnt allow to set a custom value for fps we must do it with RTTS or insane nvidia so I did 141 inside Nvidia. My question is do I need to change it to 141 even if I have the V-Sync on from nvidia or not? But then I kept on reading and also tried the low latency mode on and ultra. From my testing ( very hard to tell the difference ) I think ON gives me the lowest latency and I think ultra gives me the best Hz, frames stability of every animations but overall I do feel like I have more latency having V-sync then not having it. capping my fps at 141 in Nvidia control panel with G-Sync and low latency ultra or ON do seem to feel like im at lower latency with no tearing but its not as perfect than if I had V-Sync on…

What should I do to have the best of both worlds : low latency feeling smooth but also no hz monitor/frames issues.

Thank you.

finaltidus
Member
finaltidus

Hi Jorimt! Glad to see that you are still active here. Sorry I have some very noob questions on my recent weird observations on certain games which I play.

I have recently upgraded my monitor and graphics card to a G-Sync compatible 4k 144hz Dell G3223Q and RTX 4070. My CPU is i5-8600K so I understand that I may experience moderate to severe CPU bottlenecking. On the latest Nvdia 551.52 driver.

My current settings on NVCP are as follows with my target as having the lowest input lag following your optimal settings article.

G-Sync – ON
V-Sync – On
LLM – Ultra

All of my games stay way below the 144fps threshold without any fps limiter. The G-sync range for this monitor is 48-144hz.

Recently I play this game Robocop- Rogue City. There is no Reflex support on this game. With the above settings, my fps is around 60-70fps but with MAJOR stutters until it’s almost unplayable. It cannot be my CPU bottleneck as the CPU is around 40% utilisation. My GPU also ranges from 80-90% utilisation.

I was trying frantically to try to resolve this stutter problem but to no avail. Then for the fun of it, I just set LLM to off and tried out the game. Guess what? No stutters and GPU utlisation went to 99% most of the time. My FPS went to around 80-90fps and very smooth!

I tried to set LLM to Ultra and Off again to ensure that this wasn’t a one off event. But no. LLM Ultra=stutterfest while Off=smooth

Any reason why this is happening? Should I then set LLM as Off for my case in all games going forward for games that DO NOT support Reflex?

In my other games that have Reflex, I set it as On+Boost as default and so far no problems with it.

I understand that Reflex will override LLM regardless of the setting in NVCP.

What then should be the optimal settings in my current specs and objective in achieving lowest input lag, tear free experience and minimal stutter? I am not keen on trying every single game I have and having to tinker with the settings all the time as I have 100+ games on my PC so I would appreciate a general guide to an optimal settings.

Thank you so much!!! πŸ™‚

Thxt
Member
Thxt

Turn LLM on “ON” or “OFF”. You can find it https://blurbusters.com/gsync/gsync101-input-lag-tests-and-settings/8/. I think in ur case you want to set LMM to “ON”, just check the link i sent for jorimt’s answer.

finaltidus
Member
finaltidus

Thanks!!

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