The Nvidia G-Sync Thread

[Keysplayr]

I read in a post somewhere (not on this forum) that G-sync will not remove the microstuttering caused by multi GPU setups, i.e. the uneven rendering of frames.

This confused me a bit. I thought the g-sync device would be seated between the monitor and the gpu and therefore would reduce/eliminate any kind of stutter?

Someone please deconfuse me.

A frame will not get sent to a monitor until G-Sync "tells" it too. There isn't any possibility for tearing or stuttering. It doesn't give any opportunity for stuttering or tearing. At least down to just below 30fps. then it will behave just like normal V-Sync, or above the monitors actual refresh rate ability.

 

[DigDog]

As a FPS gamer, i'd sacrifice anything - color.. gamut .. - to get smoother frames. G-Sync is, if it delivers, the best thing i could hope for. It singlehandedly kicked back 1 year my new-parts purchase, as i'll be waiting for a good deal on a Nvidia as soon as g-enabled monitors are released.

Honestly, i can't say my crappy Hannsspree TN monitor lacks in color, sure it's not the best i've seen, but since i turn off everything DX10+ in my games (blur, godrays, fogs, etc) anyway, who cares?

(note that, G-Sync does imply that you'll need a GPU capable of keeping up with the monitor's requests .. which might not be all that easy)

 

[Whitestar127]

A frame will not get sent to a monitor until G-Sync "tells" it too. There isn't any possibility for tearing or stuttering. It doesn't give any opportunity for stuttering or tearing. At least down to just below 30fps. then it will behave just like normal V-Sync, or above the monitors actual refresh rate ability.

That was my understanding of it. So it will eliminate microstuttering as well. Thank you for a simple-to-understand explanation.

 

[wand3r3r]

A frame will not get sent to a monitor until G-Sync "tells" it too. There isn't any possibility for tearing or stuttering. It doesn't give any opportunity for stuttering or tearing. At least down to just below 30fps. then it will behave just like normal V-Sync, or above the monitors actual refresh rate ability.

Does it actually have frame pacing? According to the NV site it doesn't advertise anything about it. Maybe I've missed it since I haven't read much about it yet. Without frame pacing it cannot fix stuttering (microstutter).

 

[bystander36]

That was my understanding of it. So it will eliminate microstuttering as well. Thank you for a simple-to-understand explanation.

He was incorrect.

Microstutter is a problem when two video cards get out of sync. G-sync does not do anything to help this. It does prevent stutter induced by V-sync, however.

There are 3 places stutters can be created. The CPU, GPU and Display. G-sync only prevents the display stutters from happening.

 

[Keysplayr]

Does it actually have frame pacing? According to the NV site it doesn't advertise anything about it. Maybe I've missed it since I haven't read much about it yet. Without frame pacing it cannot fix stuttering (microstutter).

I don't know that it would even need frame pacing. If you had to ask this question, then I would totally suggest you re-examining the interview with Scott Wasson and Tom Petersen when they are discussing G-Sync.

 

[Keysplayr]

He was incorrect.

Microstutter is a problem when two video cards get out of sync. G-sync does not do anything to help this. It does prevent stutter induced by V-sync, however.

There are 3 places stutters can be created. The CPU, GPU and Display. G-sync only prevents the display stutters from happening.

How do you figure? A frame can only be drawn on the screen one way
The frame is complete and the monitor has finished drawing its last frame and ready for a new one. That is it. And that frame doesn't get delivered until G-Sync says to do so. Explain to me how anyone would experience Microstutter?
And also, bystander, two video cards are not required for microstutter. A single GPU can exhibit microstutter although not nearly as pronounced as multi GPU setups.

 

[bystander36]

How do you figure? A frame can only be drawn on the screen one way
The frame is complete and the monitor has finished drawing its last frame and ready for a new one. That is it. And that frame doesn't get delivered until G-Sync says to do so. Explain to me how anyone would experience Microstutter?
And also, bystander, two video cards are not required for microstutter. A single GPU can exhibit microstutter although not nearly as pronounced as multi GPU setups.

There are many causes of stutter. Note, I did not say microstutter, only because many people, and definitions written, do say it only happens with multi-GPU's. In either case, forgetting about the definition, stutter happens in many situations. G-sync only stops one type of stuttering.

G-sync prevents the stutter that V-sync causes. V-sync causes stutter when your FPS does not maintain your refresh rate, which causes frames to change from faster and slower frame times.

But what happens in multi-GPU stutter (microstutter) is not caused by v-sync. It is caused by having two GPU's delivering frames almost on top of each other. Now one GPU is ready, sends a frame to the display, and immediately after, the 2nd GPU does the same thing. Then there is a large delay for the next frames. That is still stuttering. G-sync may impose a little spacing in this situation, as the display still has a limit to how fast it can send images, but other than that, G-sync does nothing to evenly space out frames.

In the case the CPU gets busy, and cannot prep a new frame for the video card, a new image will not be rendered. In this case, you can get large delays occasionally. G-sync will not help the CPU from getting delayed.

G-sync only helps prevent stutter caused by V-sync. It does not help other types of stuttering.

Note: multi-GPU microstutter shouldn't be a big issue with the frame pacing solution in place on these cards, but G-sync is not what fixes it.

 

[wand3r3r]

^ That seems logical and is what I would expect unless they try "smoothing" via software. So far I haven't heard about any frame pacing.

 

[bystander36]

^ That seems logical and is what I would expect unless they try "smoothing" via software. So far I haven't heard about any frame pacing.

It shouldn't be a big issue with the frame pacing fixes, though even that doesn't fix CPU/OS imposed stuttering.

 

[wand3r3r]

It shouldn't be a big issue with the frame pacing fixes, though even that doesn't fix CPU/OS imposed stuttering.

Yeah if the drivers and possibly hardware are handling the framepacing in SLI then I agree.

The original point was that I don't think what Keys mentioned was accurate based on what I understand at this point, and I was trying to ask if there was some other information available if it works like he was saying. I think G-sync has good potential anyway.

 

[3DVagabond]

There are many causes of stutter. Note, I did not say microstutter, only because many people, and definitions written, do say it only happens with multi-GPU's. In either case, forgetting about the definition, stutter happens in many situations. G-sync only stops one type of stuttering.

G-sync prevents the stutter that V-sync causes. V-sync causes stutter when your FPS does not maintain your refresh rate, which causes frames to change from faster and slower frame times.

But what happens in multi-GPU stutter (microstutter) is not caused by v-sync. It is caused by having two GPU's delivering frames almost on top of each other. Now one GPU is ready, sends a frame to the display, and immediately after, the 2nd GPU does the same thing. Then there is a large delay for the next frames. That is still stuttering. G-sync may impose a little spacing in this situation, as the display still has a limit to how fast it can send images, but other than that, G-sync does nothing to evenly space out frames.

In the case the CPU gets busy, and cannot prep a new frame for the video card, a new image will not be rendered. In this case, you can get large delays occasionally. G-sync will not help the CPU from getting delayed.

G-sync only helps prevent stutter caused by V-sync. It does not help other types of stuttering.

This makes sense. It would seem like GSync won't help GPU induced stuttering at all because it doesn't even out the frame delivery. It makes the monitor work at the GPU's leisure. Makes sense that FPS moving up and down past 30fps could also produce issues as GSync disengages/reengages at that point. Basically giving us VSync type stuttering you explain. That's if I understand how it works. I haven't really studied it too hard since we only have press release stuff to go by.

 

[bystander36]

This makes sense. It would seem like GSync won't help GPU induced stuttering at all because it doesn't even out the frame delivery. It makes the monitor work at the GPU's leisure. Makes sense that FPS moving up and down past 30fps could also produce issues as GSync disengages/reengages at that point. Basically giving us VSync type stuttering you explain. That's if I understand how it works. I haven't really studied it too hard since we only have press release stuff to go by.

I do not know how they impose the minimum 30hz, but it would be pretty awesome if it simply forced a refresh when too much time has elapsed, then refreshed when the frame is ready.

I have a feeling, by the press videos that this may not be the case, but it could be done.

 

[Teizo]

The whole point of G-Sync is stutter free, butter smooth, image delivery. Not sure why frame pacing is even being discussed as an issue. Microstutter on SLI is virtually non-existent anyway.

 

[bystander36]

The whole point of G-Sync is stutter free, butter smooth, image delivery. Not sure why frame pacing is even being discussed as an issue. Microstutter on SLI is virtually non-existent anyway.

The whole point of G-sync is to allow the display to sync with the GPU, without imposing latency or additional stuttering as a result of the GPU having to wait for the display to be ready.

G-sync is not designed as a way to remove all forms of stutter. Just a very specific, very annoying one.

You are right that frame pacing should make the multi-GPU stutter go away, but you can see by FCAT, it isn't perfect. Though it is good.

 

[3DVagabond]

I read in a post somewhere (not on this forum) that G-sync will not remove the microstuttering caused by multi GPU setups, i.e. the uneven rendering of frames.

This confused me a bit. I thought the g-sync device would be seated between the monitor and the gpu and therefore would reduce/eliminate any kind of stutter?

Someone please deconfuse me.

The whole point of G-Sync is stutter free, butter smooth, image delivery. Not sure why frame pacing is even being discussed as an issue. Microstutter on SLI is virtually non-existent anyway.

See the other post I quoted. The question was asked, so it's being discussed. I imagine it's because standard vsync is used to fix/reduce MS and Whitestar127 read where G-sync won't do it the same way. Since we don't have any actual working examples to go by, it's all conjecture and we'll have to wait and see.

 

[bystander36]

Don't get me wrong. I am very excited about G-sync. I plan to get it, no question about it. I just recognize what they are doing, and watched all their interviews showing off the tech.

They go on and on about how smooth it makes things, and I believe it, but no where does it mention a thing about removing stuttering other than what is caused by V-sync.

I think the best way to explain it would be like this: G-sync will give frame delivery times like FCAT shows when v-sync is NOT used, but prevent the tearing that is normally present.

Visually, without v-sync, it can look a bit like stuttering, so G-sync will feel smoother than not using v-sync now.

These are all great things. Let's just not go overboard and expect it to fix things it plays no part in.

 

[Whitestar127]

Hmmmm. It doesn't seem to be quite as simple as I first thought.

I watched this video yesterday: http://www.youtube.com/watch?v=KhLYYYvFp9A and learned quite a lot from it.

At about 1:13:08 they mention SLI. Tom says: "SLI is supported out of the gate ... SLI, a key technology...and actually it makes a lot of sense...it's a little bit harder to do with G-sync, but it gets back into how do you meter and what's the right policy for metering when you have basically an infinite refresh rate asynchronous monitor."

Am I right in assuming that he touches on what we are discussing? The metering of the variance in frame rendering? This would indicate that the frame rendering variance (micro-stutter) is indeed an issue/challenge.

 

[Raghu]

Stutter is caused due to varying delta between game time and frame display time. With gsync, the delta between game time and frame display time is kept fixed. So, gsync does fix all types of stutter.

 

[moonbogg]

If a game already feels very smooth, would Gsync make a difference? Sometimes things run so well I couldn't imagine it looking much smoother.

 

[bystander36]

Stutter is caused due to varying delta between game time and frame display time. With gsync, the delta between game time and frame display time is kept fixed. So, gsync does fix all types of stutter.

If that were true, there would be no stutter without v-sync. You'd just get tearing, but we should all know that isn't true by now. (Look at all the early FCAT data.)

 

[Whitestar127]

If a game already feels very smooth, would Gsync make a difference? Sometimes things run so well I couldn't imagine it looking much smoother.

G-sync will have the same buttery smooth feeling (visually) as a game that always delivers 60+ fps when v-synced at 60Hz. At least that's how Tom described it in that video. But with G-sync you get the added benefit of reduced input lag compared to v-sync.

 

[Teizo]

See the other post I quoted.

I know. I'm not calling you out or anything. Just seems it was starting to get a bit overblown with gossip. According to Nvidia, this shouldn't be an issue. We'll seen soon enough if that is the case.

If a game already feels very smooth, would Gsync make a difference? Sometimes things run so well I couldn't imagine it looking much smoother.

In that video Linus posted with Tim Sweeny, he mentioned that you could read the letters on the clock as it was moving it was so smooth. If that is the case, which there is no reason not to believe him, then the smooth it delivers will likely be different than the smooth we have come to 'accept'.

Tom Petersen did say though that the closest example as to what G-Sync delivers is what a perfectly timed V-Sync @ 60hz (or 120hz) looks like. It just does it all the time.

 

[bystander36]

Just keep in mind, he was using a demo, which is designed to show what they want. It isn't as complicated as many games, and won't likely have game generated spikes, like some games do, or stuttering issues like others (Far Cry 3 for example).

G-sync most certainly addresses a HUGE issue, but you can't expect it to fix ever issue in games related to stutter. It simply does nothing to address many things that causes stuttering, but it does address one in a very big way and another not typically associated with stutter, but also big (tearing). It even fixes latency that V-sync has.

 

[Whitestar127]

In that video Linus posted with Tim Sweeny, he mentioned that you could read the letters on the clock as it was moving it was so smooth. If that is the case, which there is no reason not to believe him, then the smooth it delivers will likely be different than the smooth we have come to 'accept'.

Yes, but this is where it gets a little bit confusing again. The above would indicate that there is some sort of blur reduction going on.

But according to this http://www.blurbusters.com/confirmed-nvidia-g-sync-includes-a-strobe-backlight-upgrade/ you currently have to choose between the G-sync mode and a low persistence (strobing) mode similar to LightBoost that will reduce blur. So basically choose blur or stutter.

But maybe there is also some sort of blur reduction inherent in the G-sync mode. It certainly seems like that based on what I've read and the above statement from Sweeney. Guess I'll just have to wait until I can see it with my own eyes.