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.



1653 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
askobilv
Member
askobilv

A lower fps limit would rob frames

What if I want to reduce load on my GPU and CPU by capping to lower values like somewhere between 60-90 (on 144hz monitor)

Could that work or I will experience bad implications?

Jimmy
Member
Jimmy

Hi, thank you for the great articles you guys are amazing.
I have one quick question. I’ve recently bought a G-SYNC monitor 144hz and its capable of 180hz OC. The game that I play gives me around 160-170 fps. Do you recommend capping my fps @ 141 or OC the monitor and let the G-SYNC do its job while capping @ 177 ? My main goal is lower input lag with the highest fps.

18koko
Member
18koko

Hi I just want to ask if I enable low latency mode in nvidia control panel and also enble ingame low latency mode (valorant nvidia reflex on+boost) will it conflict with each another? Do I enable both or no?

christofin
Member
christofin

Hello, thank you for the wonderful article. I’ve been using a g-sync compatible monitor for a long time and have always left g-sync on, vsync on, and a framerate cap in the Nvidia control panel at 156fps with a 160hz monitor.

I think as time has gone on I’ve become more sensitive to noticing microstuttering in games. For example PUBG is an absolute stutterfest and it’s something I used to not notice. Likewise with games with awful frame pacing issues in general like Dark Souls 3. I’ve always tried to stick to games that have very smooth frametimes, like Overwatch. But even now with the reflex patch, I’ve seen a few frametime spikes here and there in Overwatch and I have to admit that it does bother me.

My question to you is this: is there something I can do system wide to reduce frame time spikes? Would turning off vsync help? I saw in the article in the stuttering section, you mentioned that if the game has a pause, no settings can fix that, but are there any settings that could mitigate how noticeable it is?

I used to try to just throw money at the hardware to mitigate stuttering. I’ve upgraded my ram and power supply, for example. Right now I have a 9900k with a mild overclock and a 3090 founders edition running at stock. I do aggressively monitor what tasks I let run in the background and I generally keep software closed while I’m playing games. Is there anything else I can do to help reduce stuttering in various games?

MrSnave
Member
MrSnave

Hello, thanks for this incredible in depth post. I have one main question regarding G-Sync that I cant seem to wrap my head around.

My settings right now are: G-Sync On + V-sync On (NVCP) + in-game frame limit to 141 (144hz monitor) + Nvidia Low Latency On.

This works perfectly for games like fortnite where I am able to get the right FPS. however, in games like Mordhau my FPS cannot reach the 140 range. My question therefore is: what do i do in cases where the game cannot reach the optimal fps? do I limit my frames to a lower number that can be reached? or do I just leave it?
I hope to hear from you soon, and keep up the great work.

wpDiscuz