G-Sync requiring very low FPS cap?

Talk about NVIDIA G-SYNC, a variable refresh rate (VRR) technology. G-SYNC eliminates stutters, tearing, and reduces input lag.

G-Sync requiring very low FPS cap?

Postby Glide » 17 Apr 2017, 17:35

So I finally got a G-Sync display - a PG348Q.
It's 3440x1440 @ 100Hz, and based on most of the advice here I should be adding a framerate cap about 2 FPS below this to prevent it from switching to V-Sync operation.

However if I disable V-Sync, I see tearing until I cap games at 87 FPS in RTSS.
Not constantly, but if I'm playing a game and I flip my view around quickly, it often exceeds that 87 FPS limit for a brief moment, and even 88 FPS can allow it to tear in that situation.
This is only seen on the monitor's FPS Counter, where I just see it hit 100Hz for a single frame. Afterburner doesn't seem to pick it up since it only allows polling at 100ms.

Is there some option that I have to change in Afterburner/RTSS to fix this? 87 FPS seems excessively low.
It's still a lot better than 60Hz of course (+27) but farther from 100Hz than I'd like. (-13)
I'm almost regretting not waiting for 144/200Hz panels with that limit - though I think it's only VA panels that are due to be released this year and I don't like them.
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Re: G-Sync requiring very low FPS cap?

Postby jorimt » 17 Apr 2017, 17:38

That's due to frametime variances, complete explanation in my article here:
http://www.blurbusters.com/gsync/gsync101-range/

Long story short, use G-SYNC + v-sync on (Nvidia Control Panel) + -2 fps limit below max refresh (98 in your case).

As long as you're in the G-SYNC range (via an fps limiter or when your system can't exceed 100 fps in a given game), v-sync isn't actually v-sync in this instance; it merely allows frametime compensation with G-SYNC enabled. G-SYNC + v-sync off does not.
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Re: G-Sync requiring very low FPS cap?

Postby Glide » 17 Apr 2017, 17:44

Oh I must have missed the part where you need to have V-Sync enabled to prevent it from exiting the G-Sync state with a framerate cap in place.
Do I still have to make sure that the monitor's FPS counter never hits 100 though?
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Re: G-Sync requiring very low FPS cap?

Postby jorimt » 17 Apr 2017, 18:16

If the monitor exceeds 100 fps at any point, with G-SYNC + v-sync off, you'll get full on tearing, and with G-SYNC + v-sync on, you'll get v-sync-level input latency.

As long as you have an appropriate in-game cap (RTSS adds 1 frame latency) of 98 (97 if you want to be super safe), you shouldn't be in danger of hitting or exceeding 100 fps, no.
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Re: G-Sync requiring very low FPS cap?

Postby Glide » 17 Apr 2017, 18:19

Hmm, I've only tested it in a couple of games so far, but I still had to drop the limiter to 93 FPS for the monitor to never report 100Hz being used.

EDIT: Make that 91 FPS.
Better than 87 I suppose.
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Re: G-Sync requiring very low FPS cap?

Postby jorimt » 17 Apr 2017, 18:43

What games, what limiters? And what are you using to report the current fps?
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Re: G-Sync requiring very low FPS cap?

Postby Glide » 17 Apr 2017, 18:52

jorimt wrote:What games, what limiters? And what are you using to report the current fps?
The last game I tried, which caused me to drop it from 93 to 91 FPS, was the original Dishonored.
Using RTSS 7.0 for the framerate limiting, and the monitor's own FPS Counter (refresh rate monitor really) to check what the display is running at, since that updates every refresh while RTSS/Afterburner do not.
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Re: G-Sync requiring very low FPS cap?

Postby RealNC » 17 Apr 2017, 19:28

This is normal. On my 144Hz monitor, I still get tearing with a 120FPS cap. G-Sync is active, but the frame time variance compensation mechanism gets disabled with v-sync off.

You need to do four things:

1. Enable G-Sync.
2. Enable vsync in the nvidia panel.
3. Disable vsync in the in-game settings.
4. Limit the frame rate to 2 (I use 3, just to be safe) FPS below max refresh.

That way, G-Sync will be always active, including the safeguard against bottom tearing. Forcing vsync in the nvidia panel DOES NOT add input lag in G-Sync mode. It just makes sure the tearline is not visible. If you read the g-sync 101 post, it's all explained there.
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Re: G-Sync requiring very low FPS cap?

Postby Glide » 17 Apr 2017, 19:35

RealNC wrote:You need to do four things:
Yes, I've enabled V-Sync now instead of letting the application decide, but I still need to cap at 91 FPS to prevent the monitor's FPS counter from ever hitting 100 in-game.
So far. It may have to be lower once I start testing more games.

With V-Sync disabled it had to be 87 FPS to prevent tearing.

EDIT: DOOM in Vulkan required the cap to be dropped to 86 FPS with V-Sync enabled.
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Re: G-Sync requiring very low FPS cap?

Postby jorimt » 17 Apr 2017, 20:22

Sounds like something weird is going on, or the built-in meter isn't accurate, and is giving false "100 Hz" positives; I'd defer to RTSS readouts in this instance. Either way, if you're not sustaining 100 fps/Hz for long periods, and it simply spikes infrequently, there isn't going to be time for noticeable input latency to build up, theoretically.
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