How can g-sync smooth the gameplay?

[sanjuro]

Hi,
first of all i have read gsync previews and did not understand them , better said only thing i understand is what it should does. Actually i have 120hz LG W2363D and i barely encounter tearing with vsync off, most games have less than 120fps, isnt tearing problem of higher fps than refresh rate? but what i really dont understand is for example here http://www.infinite.cz/blog/nvidia-gsync-dojmy when they were testing it with metro last light, they experienced same feel of smoothness with 40fps with gsync on as 80fps without gsync. How can technology which purpose is to remove tearing do this(smooth out low fps gameplay)?
I am asking bacause i want to upgrade to benq xl2720z and i dont know if i should just wait for xl2720g. thanks

[RealNC]

isnt tearing problem of higher fps than refresh rate?

First, tearing occurs when there's no synchronization between the monitor and the GPU. Framerate doesn't matter. Tearing happens even with 120FPS in 120Hz mode, since without vsync, the GPU doesn't know when to start the next frame. The only information contained in "120Hz" is that there are 120 screen refreshes per second. It doesn't tell the GPU the exact time when each refresh happens. You need vsync in order to know those exact times.

Also, more FPS than refresh rate is better then the other way around; tearing becomes less noticeable.

Now as to why gsync makes things smoother: what do you think happens when you try to display 119FPS in a 120Hz mode? At least one frame won't fit, right? So that means you get stutter. Demonstration of the problem:



With gsync, there's never a discrepancy between FPS and refresh rate. If the game runs at 40FPS, the monitor is doing 40Hz. This means that all frames will "fit" now, so there's no stuttering. Simulation of how the above would look with gsync:



Furthermore, unlike vsync, gsync doesn't make the GPU wait for the monitor; it makes the monitor wait for the GPU. This reduces input lag, since with vsync, games would get input, render the frame, and then wait for the monitor to display the next frame. This wait at the end is what causes input lag with vsync. With gsync, that doesn't happen; when the game has a frame ready, it's sent to the monitor. The monitor then updates its display as it received the frame (rather that updating the screen at fixed intervals, like non-gsync monitors.) This gets rid of both tearing as well as input lag.

If you were reading carefully, you will notice that there's a problem when the game reaches an FPS count that matches or exceeds the monitor's refresh rate. If a game reaches 144FPS on a 144Hz monitor, then gsync will behave like vsync, since now the GPU *has* to wait for the monitor. So input lag is now back. In order to make sure this won't happen, it's best to use a frame limiter with gsync. On 144Hz monitors, you would set the frame limiter to something like 142FPS. This makes sure that at all times, it's the monitor waiting for the GPU, not the other way around.

[Chief Blur Buster]

Another article is:
How Does GSYNC Fix Stutters?
Showing the relationship between eye-tracking and frame timing, and how GSYNC can smooth stutters.

[sanjuro]

thanks for your reply, this makes sense, but funny thing is that with 60hz monitor i had much more tearing than now, i dont know why it is so.
So i will ask one more simple question, do you think that gsync is worth that 150euro on 120hz monitor or how much it will be? because in that article they mention problem of more motion blur when low fps even if the game is smooth, but motion blur is that kind of thing that i cant stand, because of that i am buying 120/144hz monitor.

[Chief Blur Buster]

thanks for your reply, this makes sense, but funny thing is that with 60hz monitor i had much more tearing than now, i dont know why it is so.

At lower refresh rates, you get more tearing visiblity time per refresh cycle.
At frame rates higher than refresh rates, you can have more than one tearline per refresh cycle.
Higher refresh rates, can reduce tearing visibility time (Tearlines are is visible for only one refresh cycle, unless they keep reoccuring in the same location in the screen).

[/quote]So i will ask one more simple question, do you think that gsync is worth that 150euro on 120hz monitor or how much it will be? because in that article they mention problem of more motion blur when low fps even if the game is smooth, but motion blur is that kind of thing that i cant stand, because of that i am buying 120/144hz monitor.[/quote]
Then you will probably like the ULMB mode that is included with GSYNC. See Photos: 60Hz vs 120Hz vs LightBoost. You will get a similar experience when you use ULMB (Ultra Low Motion Blur).

However, you will need high frame rates (framerate matching refreshrate) to take advantage of any low-persistence technology now on the market (strobe backlights, zero-motion-blur). Whether it is CRT, LightBoost, ULMB, or any other low-persistence technology.

[sanjuro]

However, you will need high frame rates (framerate matching refreshrate) to take advantage of any low-persistence technology now on the market (strobe backlights, zero-motion-blur). Whether it is CRT, LightBoost, ULMB, or any other low-persistence technology.

Main reason for upgrading my monitor is actually these motion blur technologies. In csgo i have no problem at getting 120fps @ 120hz. But what about other games. From what u said it means that i cant use Lighboost(espacially benq motion blur reduction) if i have lets say 70-80fps @ 120hz?

[RealNC]

funny thing is that with 60hz monitor i had much more tearing than now, i dont know why it is so.

With 60Hz but with the same framerate (say, 100FPS), there's going to be more tearing lines per scanout. Whether this looks worse or not seems to differ from person to person. I don't own a 120Hz monitor yet, but I have access to one. The tearing in 60Hz and 120Hz looks different, but I can't say whether it's better in 120Hz or not. It's just as annoying to me.

I am also not sure whether the panel itself has something to do with it (like the panel's pixel response times.) I suspect that it does. We had some old 60Hz Dell monitors in the university labs. These were really slow (you could see a trail behind the mouse cursor on the desktop, and animations in general were blurry.) Tearing on these monitors looked much worse than the 60Hz "gamer" monitor I have at home.

A good way to test this would be to switch your monitor to 60Hz. Does it look worse in regards to tearing?

So i will ask one more simple question, do you think that gsync is worth that 150euro on 120hz monitor or how much it will be? because in that article they mention problem of more motion blur when low fps even if the game is smooth, but motion blur is that kind of thing that i cant stand, because of that i am buying 120/144hz monitor.

Gsync for me is worth it. It's the reason I'm still using a 60Hz monitor; I'm waiting for the BenQ gsync monitors to come out.

The blurring at lower framerates has two causes. The first has nothing to do with gsync. Animations at lower framerates look blurrier on all monitors, not just gsync ones. On top of that though, LCD panels have issues when driven at very low refresh rates. When you're nearing 30Hz, the pixels will start to exhibit artifacts, and this contributes to blur. LCD pixels really want to be refreshed ASAP (they're somewhat similar to RAM in this regard; if you don't refresh them quickly enough, they tend to forget their state.) However, if your games never fall below 40FPS (and thus the monitor won't go lower than 40Hz), then this won't be much of a problem.

[RealNC]

From what u said it means that i cant use Lighboost(espacially benq motion blur reduction) if i have lets say 70-80fps @ 120hz?

You can use it. But it simply won't look as nice, since some frames will be displayed twice. There's still going to be less motion blur, but because some frames are displayed twice, you will get a "double image" effect (some people describe it as "judder", which I think is not correct, but it has a similar effect.) This also happens with CRT monitors, btw.

Also note that you can't use any of the blur reduction methods (lightboost, ULMB, or any other backlight strobing tech) together with gsync. It's either gsync, or blur reduction. You can't activate both at the same time. If you can't live without backlight strobing, then that would mean you can never use gsync. So this might answer your question on how important gsync is to you right now It's personal preference. Me, I prefer stutter-free and tear-free animations (gsync) over blur reduction (strobing.)

At some point, there could be monitors out there that can do gsync and strobing at the same time. But it's probably gonna take quite a while. I wouldn't expect anything this year.

[Chief Blur Buster]

Keep in mind that you can choose a strobe technology with low minimum strobe rate, so you can use a lower refresh rate for the "nice looking zero motion blur effect".

LightBoost = minimum strobe rate 100Hz
Turbo240 = minimum strobe rate 105Hz
ULMB = minimum strobe rate 85Hz
BENQ Blur Reduction V1 = minimum strobe rate 75Hz
BENQ Blur Reduction V2 = minimum strobe rate 50Hz (with Strobe Utility)

In practical terms, 85Hz is the lowest comfortable strobe rate, while some are just fine with 75Hz. So for modern games you could run at 85fps@85Hz to get the good low-persistence effect.

That said, GSYNC is a *REALLY* good thing to have as an option in a monitor, as high-frequency microstutter creates a sensation of extra motion blur. You're still bottlenecked by full persistence of a whole refresh cycle (e.g. 1/144sec of motion blur at 144Hz is still 6.9ms full persistence -- more than any of the strobe technologies). We are rooting for higher GSYNC frame rates (e.g. 240fps@240Hz+) for flicker-free low persistence, or by adding strobing to achieve lower persistence at lower refresh rates (e.g. variable-rate strobing done without visible flicker).

[sanjuro]

thanks guys for your great answers, i understand it better now, probably i will wait for gsync monitors