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.



1486 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
DnsGaming
Member
DnsGaming

Good evening, I currently have an i7-8700k with a GTX 1080 TI.
My display is an MSI Optix MAG271cv freesync 144hz.
When I use G-Sync I have flickering black images, does this make sense?

axyloo
Member
axyloo

Can someone help me how to setup correctly ” DOTA 2 G-SYNC Setting ” ?
i have monitor 240hz

Redneval
Member
Redneval

Thanks for the guide, i don’t know much about how to get these settings to work. I reimaged my computer and now nothing works properly.

Mico
Member
Mico

Hi jorimt,

Thank you for this wonderful guide.

I encountered a weird problem when trying to follow your optimal G-SYNC settings. In my Nvidia Control Panel, the Low Latency Mode doesn’t have the “On” option, only “Off” or “Ultra”.

I’m pretty sure the “On” option used to be there. I don’t know what caused it to disappear as I didn’t not change any settings. The only difference that I noticed is that there is a message displayed on top of the Settings in NVCP saying “Windows OS now manages selection of the graphics processor. Open Windows graphics settings.” and there is a drop down menu asking me to select Preferred graphics processor. It is the same situation for both Global Settings and Program Settings, the “On” option just disappeared. High-performance NVIDIA processor has been selected as the preferred graphics processor and both GSYNC and VSYNC is turned on in NVCP. I also tried the “Restored Defaults” function and it doesn’t help. It seems that there is nothing I can do to bring back the “On” option for the Low Latency Mode. Could you help?

Here is my system’s spec:
CPU: Intel i9-10900KF
GPU: GeForce RTX 3080
RAM: 16GB
Monitor: AW3418DW 3440 X 1440 120Hz
Nvidia driver version: 461.40

Thanks again.

swollenplums
Member
swollenplums

Hi,

Thank you for the guide once again – I’ve been using and sharing this site for years.

I’m currently non-GPU and non-CPU bound with a 165hz monitor. When I use Reflex + Boost in COD Warzone I am getting a FPS cap at 158 (as expected as this is equivalent of setting Low Latency “Ultra” in NVCP).

Is there any advantage/disadvantage of keeping:
Reflex + Boost ON
vs.
Low Latency “On” + Power Management Prefer Maximum Performance + FPS Cap @ 162

(Both with G-Sync “On” and V-Sync “On”)

I know It’s a comical 4 FPS difference, but is there anything else valuable I can get using Reflex instead of Low Latency “On” in a non-GPU bound scenario?

Bonus questions if you have time:
If I’m never GPU-bound (luckily the case with a 3080 so far…) do I ever need Low Latency mode “On” if I’m always capping below refresh rate?
Would you ever recommend going above the refresh rate of the monitor + disabling sync technology + higher FPS cap?

Thanks again for your time!

wpDiscuz