G-SYNC 101: G-SYNC vs. Fast Sync


The Limits of Single Frame Delivery

Okay, so what about Fast Sync? Unlike G-SYNC, it works with any display, and while it’s still a fixed refresh rate syncing solution, its third buffer allows the framerate to exceed the refresh rate, and it utilizes the excess frames to deliver them to the display as fast as possible. This avoids double buffer behavior both above and below the refresh rate, and eliminates the majority of V-SYNC input latency.

Sounds ideal, but how does it compare to G-SYNC?

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

Evident by the results, Fast Sync only begins to reduce input lag over FPS-limited double buffer V-SYNC when the framerate far exceeds the display’s refresh rate. Like G-SYNC and V-SYNC, it is limited to completing a single frame scan per scanout to prevent tearing, and as the 60Hz scenarios show, 300 FPS Fast Sync at 60Hz (5x ratio) is as low latency as G-SYNC is with a 58 FPS limit at 60Hz.

However, the less excess frames are available for the third buffer to sample from, the more the latency levels of Fast Sync begin to resemble double buffer V-SYNC with an FPS Limit. And if the third buffer is completely starved, as evident in the Fast Sync + FPS limit scenarios, it effectively reverts to FPS-limited V-SYNC latency, with an additional 1/2 to 1 frame of delay.

Unlike double buffer V-SYNC, however, Fast Sync won’t lock the framerate to half the maximum refresh rate if it falls below it, but like double buffer V-SYNC, Fast Sync will periodically repeat frames if the FPS is limited below the refresh rate, causing stutter. As such, an FPS limit below the refresh rate should be avoided when possible, and Fast Sync is best used when the framerate can exceed the refresh rate by at least 2x, 3x, or ideally, 5x times.

So, what about pairing Fast Sync with G-SYNC? Even Nvidia suggests it can be done, but doesn’t go so far as to recommend it. But while it can be paired, it shouldn’t be…

Say the system can maintain an average framerate just above the maximum refresh rate, and instead of an FPS limit being applied to avoid V-SYNC-level input lag, Fast Sync is enabled on top of G-SYNC. In this scenario, G-SYNC is disabled 99% of the time, and Fast Sync, with very few excess frames to work with, not only has more input lag than G-SYNC would at a lower framerate, but it can also introduce uneven frame pacing (due to dropped frames), causing recurring microstutter. Further, even if the framerate could be sustained 5x above the refresh rate, Fast Sync would (at best) only match G-SYNC latency levels, and the uneven frame pacing (while reduced) would still occur.

That’s not to say there aren’t any benefits to Fast Sync over V-SYNC on a standard display (60Hz at 300 FPS, for instance), but pairing Fast Sync with uncapped G-SYNC is effectively a waste of a G-SYNC monitor, and an appropriate FPS limit should always be opted for instead.

Which poses the next question: if uncapped G-SYNC shouldn’t be used with Fast Sync, is there any benefit to using G-SYNC + Fast Sync + FPS limit over G-SYNC + V-SYNC (NVCP) + FPS limit?

Blur Buster's G-SYNC 101: Input Lag & Optimal Settings

The answer is no. In fact, unlike G-SYNC + V-SYNC, Fast Sync remains active near the maximum refresh rate, even inside the G-SYNC range, reserving more frames for itself the higher the native refresh rate is. At 60Hz, it limits the framerate to 59, at 100Hz: 97 FPS, 120Hz: 116 FPS, 144Hz: 138 FPS, 200Hz: 189 FPS, and 240Hz: 224 FPS. This effectively means with G-SYNC + Fast Sync, Fast Sync remains active until it is limited at or below the aforementioned framerates, otherwise, it introduces up to a frame of delay, and causes recurring microstutter. And while G-SYNC + Fast Sync does appear to behave identically to G-SYNC + V-SYNC inside the Minimum Refresh Range (<36 FPS), it’s safe to say that, under regular usage, G-SYNC should not be paired with Fast Sync.



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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