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.



3099 Comments For “G-SYNC 101”

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Sort by:   newest | oldest | most liked
dandyjr
Member
dandyjr

Hello there! I recently bought a 500Hz G-sync monitor and it’s the first time I’ve owned a true G-sync monitor with a module. The exact model is the AW2524H. One of the first things I noticed with this monitor is that the frames never hit the max range of the monitor as if the module has it’s own way to prevent leaving the G-Sync range. The monitor is technically a 480Hz panel but it has a factory overclock you can set to 500Hz. In stock form (with all of the proper G-sync settings in the control panel) the frames automatically are capped at 477 and never will hit 480. Overclocked to 500Hz, The frames will never go above 496. I tested multiple games just to make sure and they all produced the same results. What I’m wondering is if this is an effect of this specific model or if this is true for all G-Sync native monitors. Does this mean that I never have to cap my fps because the monitor won’t allow the frames to hit the ceiling anyway? I noticed that if I enable reflex in supported games, the frames will be capped at 438 instead of 496. My guess is that Nvidia set such a low limit to be safe for G-Sync compatible monitors that happen to be 500Hz (since I’ve heard they are less accurate and will leave range more often). What are your thoughts on this? I’d be stoked to hear that I don’t have to cap my fps anymore but it seems too good to be true haha!

IggyRex
Member
IggyRex

Hello, you probably get asked this a lot, but I game on a lg c1 at 120hz, and I was wondering what would be best for my setup. I am currently using Vsync – on in the control panel, but I am unsure if I should set low latency to ultra or if setting to On would be the better option for me. Having it set to ON would require me to set an fps limit on a game basis correct? So something like elden ring would work better being capped to 59 or 57fps as opposed to it set to ultra which would do it for me. What are the benefits of either option? Sorry, and please let me know. I just want to get the most out of my hardware and out of gsync.

Kaffik
Member
Kaffik

Hi!
I have 165 Hz G-Sync Compatible (ls27ag500nuxen) monitor.
I used all your tips for this type of display but something irritates me a lot.
60 fps on my screen looks like 30-35 at best, I need to have like 95-100 fps to make it look like smooth 60.
For example my boyfriend has 144 Hz VRR TV and 60 fps looks like 60 fps.
I have DP 1.4 and VRR on.
Do I really need a G-Sync module to make it better?

Indignified
Member
Indignified

Hello, is there any point of having gsync or reflex on if fps is uncapped?

ChillyWilly219
Member
ChillyWilly219

Hello, on my LG Ultragear OLED 45GR95QE-B monitor I have experienced flickering in games like Lords of the Fallen or Hellbalde, even in Warzone. A slight flicker mainly in the menus and loading areas. Is there a solution to this problem? Many people say to turn off g sync directly. What do you recommend me?. Greetings.

wpDiscuz