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[Thread Superseded] G-Sync 101 w/Chart (WIP)

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

Re: G-Sync 101 w/Chart (WIP)

Postby drmcninja » 28 May 2017, 23:51

Awesome, can't wait for your article, it's going to be a huge knowledge bomb. There's so much pseudo-science being spread online about this subject.

120Hz w/300 fps and Fast Sync is a little over a 2x ratio, which is enough excess frames to get you within a few milliseconds of G-SYNC input latency, but since Fast Sync drops frames, you're not going to get near as smooth frame pacing. But yes, in that situation, it is much better than uncapped double buffer v-sync input latency-wise.
Yeah, uncapped v-sync is terrible, but would it be better than V-Sync with framerate limited to 1-2fps below refresh rate (or even just a few decimal points below)? (No G-Sync in this situation)
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Re: G-Sync 101 w/Chart (WIP)

Postby RealNC » 29 May 2017, 00:30

Fast sync with frame rate capped below refresh would give you the same latency as vsync with the same cap.
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Re: G-Sync 101 w/Chart (WIP)

Postby Sparky » 29 May 2017, 01:53

drmcninja wrote:So if I'm reading you correctly, using RTSS means you can just use G-Sync and do not need to enable V-Sync at all? Then why doesn't everyone just do this rather than enabling V-Sync which might introduce extra input lag?

And correct me if I'm wrong, RTSS alone can't help me if I don't have G-Sync, right? I'll need to use either V-Sync or Fast-Sync to get rid of tearing? Or can I set RTSS @ my refresh rate and hope for the best? There's no impact on input lag with RTSS either, right?

RTSS adds 1 frame of input lag over an in-game framerate limiter. G-Sync +V-sync add input lag only in the case that framerate goes above the max refresh rate of the monitor. Even then, unless average framerate is higher than refresh rate, the difference in latency will be limited to the variance in frametime. Basically if you have a tear at the bottom quarter of a 144hz g-sync monitor, v-sync on at 143fps will turn that tear into a 1.7ms delay for the frame at the bottom of the tear. RTSS at that framerate would add about 7ms of delay.

Fast sync should add a random amount of lag between 0ms and 1/framerate, compared to g-sync capped in game. So at 300fps that would be about 1.7ms on average. V-sync on capped below the refresh rate(without g-sync) will behave the same, but will have more judder due to the lower framerate.
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Re: G-Sync 101 w/Chart (WIP)

Postby drmcninja » 29 May 2017, 02:26

Sparky wrote:
drmcninja wrote:So if I'm reading you correctly, using RTSS means you can just use G-Sync and do not need to enable V-Sync at all? Then why doesn't everyone just do this rather than enabling V-Sync which might introduce extra input lag?

And correct me if I'm wrong, RTSS alone can't help me if I don't have G-Sync, right? I'll need to use either V-Sync or Fast-Sync to get rid of tearing? Or can I set RTSS @ my refresh rate and hope for the best? There's no impact on input lag with RTSS either, right?

RTSS adds 1 frame of input lag over an in-game framerate limiter. G-Sync +V-sync add input lag only in the case that framerate goes above the max refresh rate of the monitor. Even then, unless average framerate is higher than refresh rate, the difference in latency will be limited to the variance in frametime. Basically if you have a tear at the bottom quarter of a 144hz g-sync monitor, v-sync on at 143fps will turn that tear into a 1.7ms delay for the frame at the bottom of the tear. RTSS at that framerate would add about 7ms of delay.

Fast sync should add a random amount of lag between 0ms and 1/framerate, compared to g-sync capped in game. So at 300fps that would be about 1.7ms on average. V-sync on capped below the refresh rate(without g-sync) will behave the same, but will have more judder due to the lower framerate.
About how much lag is added for each frame below the refresh rate with V-Sync capped in-game? i.e, 119fps/120Hz, 118fps/120Hz, 117fps/120Hz, etc.

Vsynctester shows my monitor stays mostly just barely over 120Hz and with 120fps cap, I feel like it's sometimes responsive, sometimes not and at 121fps, there's full blown v-sync lag. So I dialed it back to 119fps, not sure if I should go to 118 to be sure.

With 144Hz, I'm uncertain about how stable framerates are so I wouldn't go over 142.
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Re: G-Sync 101 w/Chart (WIP)

Postby Sparky » 29 May 2017, 02:53

drmcninja wrote:About how much lag is added for each frame below the refresh rate with V-Sync capped in-game? i.e, 119fps/120Hz, 118fps/120Hz, 117fps/120Hz, etc.
Not a whole lot. 117 would be something like 0.1ms more latency on average than 120. The difference gets bigger as framerate drops(as in the difference between 59 and 60 is bigger than the difference between 119 and 120). The framerate cap shouldn't change the amount of calculation time, so really it's just the change in frametime, (and half that, because your input event timing is random compared to when the frame starts).
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Re: G-Sync 101 w/Chart (WIP)

Postby drmcninja » 29 May 2017, 17:32

For some reason, V-Sync at 119fps/120Hz feels better than Fast-Sync at 300fps/120Hz. It looks slightly smoother/more synced, but there's no real tearing in either and Fast-Sync is pretty much as smooth. And the mouse feels a little laggier in V-Sync, but it's so subtle that I still aim far better in V-Sync. No idea why. I can just see and aim at targets easier.
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Re: G-Sync 101 w/Chart (WIP)

Postby Sparky » 29 May 2017, 20:50

Try fast sync at a multiple of your refresh rate. Or even exactly your refresh rate.
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Re: G-Sync 101 w/Chart (WIP)

Postby YukonTrooper » 29 May 2017, 21:46

In your testing has there been any engine-specific input lag due to running within the G-Sync polling range? I know the subject has been touched upon in the past, but I also think I remember reading Nvidia was going to address that phenomenon.
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Re: G-Sync 101 w/Chart (WIP)

Postby RealNC » 29 May 2017, 21:55

YukonTrooper wrote:In your testing has there been any engine-specific input lag due to running within the G-Sync polling range? I know the subject has been touched upon in the past, but I also think I remember reading Nvidia was going to address that phenomenon.

There's g-sync disabled vs g-sync enabled results. That's exactly what you're asking for.
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Re: G-Sync 101 w/Chart (WIP)

Postby drmcninja » 30 May 2017, 05:58

Sparky wrote:Try fast sync at a multiple of your refresh rate. Or even exactly your refresh rate.

So 240fps kind of works, but there's still a little bit of tearing. I made it better by putting on Antialiasing ('Low - FXAA') to make it seem smoother.

I don't know if it's in my head but 240fps looks better than 300fps and feels better too.

120fps leaves noticeable tearing. 130fps has good mouse response, but still some tearing. Over that I start to get really bad stuttering until near 200 again.

Fast-Sync @ 240fps or 130fps has better mouse response than V-Sync @ 119fps, but V-Sync still looks so perfectly tear-free and smooth that it kind of boosts my aim a little bit anyway. I mean the bit of 'lag' I notice in V-Sync over Fast-Sync is very slight but still there. I have greater precision/accuracy in V-Sync but in Fast-Sync I can literally aim faster with a still pretty good degree of precision/accuracy so I guess I'll keep experimenting to see which is better for me.
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