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.



977 Comments For “G-SYNC 101”

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compddd
Member
compddd

My monitor is 144Hz but if I’m playing a game like Sekiro Shadows Die Twice which has a max FPS limit of 60 due to being a console port, do I set my FPS limiter to 57 FPS for that game in RTSS?

svatt
Member
svatt

Hi guys, i have bunch of problems with freesync.
My pc: r5 3600, rtx 2070, 144hz freesync monitor

My problem is that normally when i turn on gsync compatible in NVCP(i also turn on gsync indicator) its not working games are just stuttering and indicator is not showing, BUT when i go to any game properties and i disable thing called “disable fullscreen optimalisation” gsync compatible(“freesync”) starts working and indicator start showing but im noticing heavy flickering(i know its normal in loading screen but im noticing it like every 10sec. in game playing). okay so that is my first problem, second is why when i restart my computer and i have enabled gsync compatible but NOT DOING that thing in game properties(disabling fullscreen optimalisation) gsync compatible just starts working and again with high flickering.
Gsync compatible is just sometimes working and sometimes not after restarting pc. I go to the shop where i buy monitor and they replace monitor for the same model but problem is stil here. Is there any way to slove it or i must buy certified Gsync compatible monitor wich is in Nvidia list or is there problem in any hardware part like GPU or MB?

thanks for any help and sorry for my english but im from slovakia.

Jhaniel
Member
Jhaniel

So GSYNC ON, VSYNC ON. In game settings VSYNC OFF and cap fps to 141 if I have a 144hz monitor? Anything else TIA

DeepskyScorpion
Member
DeepskyScorpion

I would like to ask if the behaviour of VSYNC with GSYNC enabled on an Nvidia GPU — where the module deals with frame time variance better and doesn’t allow suddent changes in frame time to introduce tearing — applies to Freesync monitors, with GPU from both venders? Or do the GPU and/or the display treat it differently depending on the venders of both components?

stollywood
Member
stollywood

Hi there,

Great article!!

I have 8700k and 2080ti and when running at 1440p on high settings I’m having some stuttering So tried to run gysnc on, vsync on (nvc), llm on & and in game limiter 3fps under my 144hz refresh.

Problem is im hitting 100% gpu usage when i look in. Hw monitor when play destiny 2 and COD MW.

What is the best thing to do?

I have changed some options in nvidia control via some other guides and not sure if that is causing it.

Surely my gpu being 2080 ti sound run under 100% all all of the time. Temps are around 82oC max

Cheers Ryan

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