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.



1365 Comments For “G-SYNC 101”

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oliverds
Member
oliverds

Hello Jorimt,

i am a bit confused about the combination of G-Sync and V-Sync.

I am running the following system:

Intel 8700K @ 5 GHz / Gigabyte Aorus Extreme 2080ti Waterforce / 32 GB RAM DDR4-3000 / LG 34UC89B with native G-Sync.

I usually do simracing, espeacially with Assetto Corsa, which is a very CPU-intense simulation (only uses one core), so that the cpu can often reach 94% occupancy when having 50-70 cars on the track.

To reduce the cpuz occupancy, i use a framelimit of 70, in some situations the fps can go down to 55, but this does not bother me.

In the NVCP, i set G-Sync on and use the max. aviable refresh-rate of the monitor. Beforce beeing confronted with several videos, i was using G-Sync together with Fastsync activated in the NVCP, but now i think that this combination isn’t really the best.

What is the best combination of a low input-lag and acceptable cpu-occupancy? G-Sync with activated V-Sync and my 70 FPS-cap? This is really confusing.

With best regards and thanks in advance,

Oliver

TheBeker1
Member
TheBeker1

I’m having trouble with micro stutter, present in all games, i followed the guide, and even tried to clean install drivers and windows, but the stutter is still present, even in the NVIDIA Pendulum demo, the stutter happens inconsistenly, but and of course, there’s a framerate fluctuation that happens with it, i have a 1080Ti and a 9600k, 16gb of ram, and a 1tb SSD.

One of my friends has the same problem, and i’ve seen that is not uncommon on forums, can i blame faulty hardware. or is there something more i can try?

gzmm
Member
gzmm

Hey, i have a 144hz gsync compatible monitor, with 48~144hz range.
If i put the monitor at 120hz, the gsync still work? This will make a 60 fps game looks smooth?

andro92
Member
andro92

First of all thank you for your amazing work.

Now if i understand it all correctly, the optimum usage is this:

Nvcp vsync on, gsync on, frame cap -3/141fps (140 for me thanks to my ocd 🙂 i dont wanna bother with additional app rtss. The latest nvcp frame cap should be on par right ? So set and forget situation from nvcp.

Now my confusion comes from ullm. I have a good cpu. 9900k overclocked to fixed 4.9ghz at all times. Im using windows high perf power plan as well. Gpu is 2080s at 1440p. 32 gig 3733mhz cl16 ram, m2 ssd, clean windows 10 pro without bloatware (again thanks to my ocd). Also i have custom water loop so temps are all ok.

If i set ullm on or ultra all times(set & forget) will i see any negative effect ?

Sample1: game runs at 40-80 fps, gpu bound
Sample2: game runs at set fps cap 140, no gpu bound
Sample3: game runs at 60fps internal limit(mortal kombat 11, ds3, sekiro) no gpu bound.
Sample4: no sync, fixed refresh rate, gpu bound vs no gpu bound.
Note: cpu usage is always low, mostly below 30 but i understand system hiccups can happen even with the cleanest systems.

And what is the difference between on/ultra/ingame reflex ?

Effect of nvcp power management mode ? Should i leave it at default or choose maximum performance. Its ok if it consumes more power.

I’m fan of set&forget type of usage and i dont care if ullm ultra adds another fps limit below my fps limit for some specific game. But i dont want extra input lag or some bug.

My second question:

I was competitive Overwatch player, now i play Mortal Kombat 11 competitively. Motion blur, backlight strobing etc not as important in this but input lag is important. Even 1 frame matters in this game to take your turn. This game designed around 60 fps and it does not strain my gpu however it fluctates between 58-60. What settings are best for this specific game ? Can ullm on or ultra add more input lag if i set&forget ?

And the last topic sorry for wall of text:

Now gsync monitors are 30-144, gsync compatibles are 48-144. My question is how seamless is this this “lfc” or hz doubling/tripling. If my game runs between 40-60 fps is it better to just disable gsync for more fluid experience. What happens at the exact moment when the lfc kicks in ? What is the difference between adaptive sync and gsync module in this topic ?

blabliblu
Member
blabliblu

Thank you for this article.

The main reason I wanted to enable G-Sync (Freesync, in my case) was because playing AC: Valhalla on 4K on my RTX 3080 with V-Sync on causes heavy stuttering when the game drops below 60 FPS, while without V-Sync there’s massive tearing action going on (every 2-3 seconds, it’s horrible.)

Now, I might be missing something here, and I understand what’s written in the article, but if I enable G-Sync, and enable V-Sync on top of it in the Nvidia Control Panel, I still suffer from the same exact stuttering when the game drops below 60 FPS. And indeed, disabling V-Sync stopped the game from stuttering and fixed the issue, with the occasional and very rare tearing compared to a non-V-Sync experience, which is a trade-off I can live with.

So, what gives? Should I just keep V-Sync off, then? Or maybe set my V-Sync to “Fast” in the Nvidia Control Panel?

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