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Tearing with g sync

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.

Tearing with g sync

Postby buzinski » 05 Jan 2019, 05:41

I bought a new dell alienware aw2518h and wanted to see if gsync is worth the money as they say it *eliminates* tearing. So at first I was curious to see if tearing would change from 60hz all the way to 240 hz using witcher 3 (no gsync for now) and I was surprised to see that even if the framerate was always the same(50-55) there is way less tearing at 240hz than at 60hz, almost to the point of it being acceptable, almost. Wasn't the fps supposed to be higher as well in order for the tears to last less time, not just the refresh rate of the monitor? I mean I'm happy it behaves like that, but if someone can explain I'd appreciate it.

Now the real problem came when I test gsync at all available refresh rates and found out it only *eliminates* tearing, in witcher 3 at least, for 144hz and up. Below 144hz it only reduces it, and I know there's no reason to set the refresh rate below 144hz but still it doesn't work as advertised. Also I tested some other games : Vampyr, Bioshock Infinite and Dirt 3 for tearing at 240hz with g sync ON and dirt 3 showed some tearing(less than 240hz with g sync OFF but still..). Can an old game like dirt 3 not run properly with gsync so the tearing is somehow the game's fault or is the monitor faulty? Or is g sync an even bigger scam?
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Re: Tearing with g sync

Postby jorimt » 05 Jan 2019, 11:13

For an explanation on why G-SYNC can still tear, start by reading this:
https://www.blurbusters.com/gsync/gsync ... ettings/2/

I'm also including a post I made in the article's comment section on this subject:
I’ve explained this ad nauseam (including in this article), but I’ll try to break it down as clearly as possible yet again…

Within the G-SYNC range (e.g. within the refresh rate), G-SYNC is V-SYNC, and V-SYNC is G-SYNC.

The “V-SYNC” option in the “on” position with G-SYNC enabled was originally a non-optional part of G-SYNC. It was only at a later point Nvidia revealed the V-SYNC “on/off” option in the control panel so that the screen would tear with V-SYNC “off” when the framerate exceeded the G-SYNC range/refresh rate, instead of reverting to V-SYNC behavior.

However, the V-SYNC option also has a role within the G-SYNC range/refresh rate as well…

Simply put, without the V-SYNC option “on,” G-SYNC can only avoid tearing within a certain transition time range; if the frametime difference between one frame and the next is too great for G-SYNC (e.g. if the new frame doesn’t begin close enough to the start of the next scanout) and the V-SYNC option is set to “off,” it will allow tearing within the G-SYNC range/refresh rate.

With the V-SYNC option “on” (a function I refer to as “frametime compensation” in the article), it will allow the G-SYNC module to hold the frame just long enough before delivery (we’re talking fractions of a millisecond here in the majority of instances when compared to “off”) to avoid tearing in these specific instances.

Your lag/performance savings with the V-SYNC option “off” over “on” with G-SYNC enabled is literally the tearing you’ll see, nothing more. And you’re only going to see tearing when a frame transition is very abrupt (like a frametime spike during asset loads, or frametime variances just near the very top of the G-SYNC range/max refresh rate).

The steadier your frametime performance/framerate are, the less tearing you will see with G-SYNC + V-SYNC “Off,” which is going to entirely depend on the given system and the given game and the interaction between the two.

TLDR; G-SYNC + V-SYNC “On” is original/absolute/complete G-SYNC that avoids tearing 100% of the time. G-SYNC + V-SYNC “Off” is spin-off/adaptive/incomplete G-SYNC that will tear if it needs to (even inside the G-SYNC range) in order to deliver the frame as fast as possible in instances were frametimes differences between the previous and next frame are too large/abrupt for G-SYNC to avoid tearing.

Finally, for optimal, tear-free G-SYNC settings, read here:
https://www.blurbusters.com/gsync/gsync ... ttings/14/
Author: "G-SYNC 101" Series

Display: Acer Predator XB271HU OS: Windows 10 MB: ASUS ROG Maximus X Hero CPU: i7-8700k GPU: EVGA GTX 1080 Ti FTW3 RAM: 16GB G.SKILL TridentZ DDR4 @3200MHz
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Re: Tearing with g sync

Postby buzinski » 05 Jan 2019, 15:24

Thanks for your response. That article advertises g sync better than nvidia :lol: .

Regarding g sync+ vsync as being the *best* choice, does that not mean the input lag is back?So in my case, that is 240hz of which I get to 150 max, should I stick to g sync+v sync and no limiters? Is there much of an input lag advantage in this case compared to traditional v sync?
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Re: Tearing with g sync

Postby jorimt » 05 Jan 2019, 20:48

No, so long as the framerate is within the G-SYNC range, G-SYNC + V-SYNC "On" does not bring back the input lag of standalone V-SYNC. And G-SYNC + V-SYNC "On" isn't so much the "best" choice, as it is the "100% tear-free" choice, which is obviously the original intent of G-SYNC functionality.

A 240Hz scanout (aka the time it takes to complete a single refresh cycle) is extremely fast, and at any framerate; the faster the scanout, the less time there is for tearing, effectively.

This means on a 240Hz display, G-SYNC + V-SYNC and G-SYNC + V-SYNC OFF are virtually the same (give or take 1ms) input-lag-wise, within the G-SYNC range. And again, the only input lag advantage G-SYNC + V-SYNC OFF is going to have is when you see tearing; that is your literal, visible lag reduction.

So as long as your framerate is below 240 (either naturally, or with RTSS or an in-game limiter of -3 FPS; at 240Hz, 237 FPS), and you are using G-SYNC + NVCP V-SYNC, you're getting the lowest input lag you can possibly have without tearing.

You'll only get standalone V-SYNC input-lag levels if your framerate exceeds your 240Hz refresh rate at any point with G-SYNC + V-SYNC "On," which is why an FPS limiter is required to keep framerates in the G-SYNC range to avoid V-SYNC-level input lag if the framerate can otherwise exceed the max refresh rate.

At 240Hz, a single frame of input lag is 4.2ms. Standalone V-SYNC with framerates above the refresh rate, can accumulate up to 6 frames of input lag. At 240Hz, that equals up to 25.2ms of additional input lag over both standalone V-SYNC OFF and G-SYNC + V-SYNC on/off within the G-SYNC range (either with a -3 FPS limit, or average framerates that fall naturally below the refresh rate) at the same framerate.
Author: "G-SYNC 101" Series

Display: Acer Predator XB271HU OS: Windows 10 MB: ASUS ROG Maximus X Hero CPU: i7-8700k GPU: EVGA GTX 1080 Ti FTW3 RAM: 16GB G.SKILL TridentZ DDR4 @3200MHz
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Re: Tearing with g sync

Postby Chief Blur Buster » 06 Jan 2019, 01:59

Regarding 6 frames of lag:
The number quite varies, depending on the driver, graphics card, whether SLI/CrossFire is in use or not, any framepacing behaviour in the driver, the "Number of Prerendered Frames" in NVInspector, the game engine internal frame handling behaviour, etc. It's often averaging a couple of refresh cycles worth of lag, most of the time in many games from many tests.

buzinski wrote:Thanks for your response. That article advertises g sync better than nvidia :lol: .

And thanks for the compliment on Jorim's article!
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Re: Tearing with g sync

Postby jorimt » 06 Jan 2019, 09:10

Yup, 6 frames is worst case, 2 frames is the average with standalone V-SYNC paired with framerates above the refresh rate. Though honestly, when directly compared to lower refresh rates, 240Hz is low lag in pretty much any scenario.
Author: "G-SYNC 101" Series

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Re: Tearing with g sync

Postby buzinski » 06 Jan 2019, 10:56

Well you've pretty much made it all clear. Now I can properly enjoy this monitor without any suspicions :D
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Re: Tearing with g sync

Postby jorimt » 06 Jan 2019, 11:39

Good to hear ;)
Author: "G-SYNC 101" Series

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