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.



273 Comments For “G-SYNC 101”

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Phroster
Member
Phroster

Why is it, that in most games, borderless fullscreen + gsync, gives worse results then exclusive full screen mode? (uneven frametimes, micro stutters)
Using a frame limiter to set the framerate -3 below the refresh rate makes it even worse when using borderless fullscreen.

I did find that G-sync + Fast sync + borderless fullscreen seems to give better results in some games. Still limiting the frame rate in borderless fullscreen, introduces microstutters.

Why is borderless fullscreen so unreliable with gsync enabled?

jdawg
Member
jdawg

Hey, so I didn’t know about turning on V-sync in NVCP only, but before I did that I was getting the occasional stutter even though the action on screen wasn’t that intense. I have RTSS showing a graph of FPS and I notice there are several little dips happening every second. The game moves smooth but then I get the stutter occasionally. I’ve closed everything unnecessary but maybe there’s more to close…not sure what other processes I can close in Windows 10 and I haven’t done any optimizations like in Windows 7.

Fast forward to setting it up as recommended here (141 FPS limit in game for my 144Hz monitor, G-sync on, V-sync ON in NVCP only, V-sync OFF in-game) and I noticed that the dips on the graph are even deeper…however I haven’t seen a stutter yet and the game plays very smooth with no lag. Any explanation for those dips in the graph though?

metalpizza123
Member
metalpizza123

Hi hi, Just a quick heads up for users with several displays of varying refresh rates. Windows will sometimes only report the lowest refresh rate monitor as the system-wide V-Sync target. After testing on driver ver 436.02, with 3 different monitors, here are my findings. I testeed with 3 games, all had similar behaviour. I used the recommended settings as per the guide.
NVCP V-sync ON
Gsync Enabled
Ingame FPS Limiter or RTSS used
Ingame Vsync/buffering disabled

Main monitor :G-Sync, 144hz.
Second Monitor 60 Hz
In game Framerate 60~

Main monitor :G-Sync, 144hz
Second monitor 75 Hz
In game Framerate 75~

Main monitor G-sync,144hz
Second monitor, 60hz
third monitor, 75hz
In game framerate 60~

Only main monitor: G-Sync 144hz
In game frame rate 140~

There’s probably a way to disable this, but for now I’ve resorted to just unplugging my other monitors. Just a note for any multi monitor users. I wish I could test more, but I just wanna play games.

kucki
Member
kucki

Should we use the “Low Latency Mode” On or Ultra with G-Sync?

Chief Blur Buster
Admin

Possibly beneficial for uncapped GSYNC + VSYNC ON. Will need to be tested.

This will reduce lag differential of below-Hz (GSYNC behavior) versus match-Hz (VSYNC ON behavior).

Creakffm
Member
Creakffm

Hello Guys, really Intresting Article/Guide but i wanna know something from you.

i Playing Games since 20 Years i know in Old Times with 60 HZ Monitors i play Competitive Games with VSYNC off to get most FPS ingame.

So back to 2019.

Im Using a Nvidia Geforce 1080 TI and my Monitor is 240 HZ DELL Alienware AW2518HF with GSYNC on Displayport Cable.

i wanna Optimizing all to Play Competitive. Actual i play with Ingame Fortnite Framerate Limit 240 HZ because see this by a lot of People.

When i wanna get less Inputlag i set in Nvidia Inspector Framerate Limiter to 245,244 ( more FPS than HZ or less and than which one is best? )

thanks for Answering

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