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.



1796 Comments For “G-SYNC 101”

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BlackStorm82
Member
BlackStorm82

Hello, is it true that the monitor with the GSYNC module contains GPU scaling?

And is it also true that GSYNC module monitor cannot use display scaling?

If GPU scaling is forced on the GSYNC module monitor. GPU scaling is used as “no scaling” in the NVIDIA control panel, and if the resolution and direct resolution of the game are the same, it doesn’t work anyway?

Also, is it the same story for GSYNC compatible monitors or only GSYNC module monitors?

Deus_nsf
Member
Deus_nsf

Please take a look at this, we may have a solution for the windowed mode nightmare that doesn’t require owning an adaptive sync display!!! https://steamcommunity.com/app/993090/discussions/0/3053989078739351832/?ctp=4

biggydeen
Member
biggydeen

Hi,

First I like to thank you for this awesome guide. I’m sure you helped tens of thousands of people to get the best out of their g-sync/freesync screen.

I do have a question no one else could anwser. Maybe you know what is going on with my system and if it is related to g-sync/freesync.

My current settings:

  • 144hz screen (LG 27GL850 Ultragear, G-sync compatible)
  • G-sync (fullscreen mode) on
  • V-sync on in NVCP
  • Framelimit 140 in RTSS
  • Core park on
  • Turned off vsync ingame and any buffers if they are available
  • Low latency mode is set to “on”.
  • Basically, exactly what you mention as the optimal settings. I’m not using any overlays like g-force exp. and RTSS.

    My problem:

    I’m expieriencing some kind of (micro)stuttering when my frames drop below 140. But it’s application dependent. For example:

    When i’m playing Battlefield V on the smaller snowmap (without the train) I constantly get 140 fps. This map runs butter smooth as I would expect with free-sync. Other smaller maps also run butter smooth. When playing the bigger snow map (with the train) and fps sometimes dips below 140 (like 135) i’m expierincing some kind of stuttering. It’s just not smooth like the smaller maps. Now this confuses me because it’s only dipping 5 frames or so below my FPS cap. But the difference for me is night and day. I have the same expierence on all maps in BF V where the frames drop just a bit below my limit.

    When I run the Timespy benchmark, everything is butter smooth. But i’m no where near my fps cap. In the first demo the FPS is going all over the place dipping to 60 and all the way up to 120 but everything looks butter smooth.

    When playing Sea of Thieves I have the same problem as BF 5. When FPS goes down the smoothness is gone. Eventhough FPS is above 100.

    It’s definitely not a hardware problem (unless my screen is the problem). I’ve had the same issue with completely other hardware. I already have a new cpu, gpu and ram. Same issue’s.

    To give you an idea what i’m expierencing:

    I did expierence the same thing when I was still using a 60hz screen + vsync. If FPS dropped below 60, even if it’s 1 frame, the smoothness is gone. That would be expected with a 60hz + vsync but I would not expect this with free-sync only dropping a few frames and way above 130 fps.

    The strange thing is, this does not always happen. Like the timespy example, everything is butter smooth but the FPS is not even near the fps cap. So, free-sync is working just fine.

    Do you have any idea what i’m facing here? Could it be CPU related because BF5 is very CPU heavy and basically always hits 100% cpu use ( i’m running the 5800x). But some cores are actually running 100% on the small now map (I checked) but on that map everything is butter smooth.

    wellroman
    Member
    wellroman

    Hi, I’m here for an advice and I hope I’ll get one from smart people. I bought 165hz monitor with g-sync and I want to use it but I really do care about my input delay so I want to know what option is going to be the best in my situation:

    1. 165 hz monitor + 162 in game fps lock + g-sync on + v-sync on
    2. 165 hz monitor + 162 in game fps lock + g-sync on + v-sync off
    3. 165 hz monitor + 180 in game fps lock + g-sync off + v-sync off

    So the questions are:

    • Does the v-sync even make sense with g-sync and will I get less input delay by turning v-sync on or by turning it off (while with g-sync)?

    • Should I even use g-sync? Is there a big difference in the input delay between the option 1 and option 3 in my list?

    I hope you got my questions right and will help me))

    xpnkz
    Member
    xpnkz

    Beautiful, this is like the holy grail when it comes to G-Sync information, thanks.

    I just want to ask over to be sure, since I recently switched to a Nvidia GPU with a G-Sync Compatible display and reading the comments I saw some conflicting comments too, specially since late driver updates seems to have changed a bunch of things (for example no more display selection under G-SYNC tab, but just says “Set the G-SYNC capable display as the primary display”).

    So for the best results, all I have to do in Nvidia Control Panel is:

    ● G-Sync: “ON” (Fullscreen) in the G-Sync tab and Monitor Technology set to “G-Sync” too?
    ● Vertical Synchronization: “V-Sync ON” (not Fast Sync)
    ● Low Latency Mode: “ULTRA”
    ● Max Frame Rate: “141” (my monitor is 144Hz)
    ● In game: V-Sync or related settings all OFF

    If someone can quickly glance over this and say if it’s correct, thanks!

    wpDiscuz