Understanding Frame rates and ATW (Asynch Time Warp)

[DerekSpeare]

Hi friends,

 

It's believe it's instructive for VR users to know the relationship between the base simulation frame rates and the Oculus ATW frame rates. Surely, most folks know this, the ones who are experienced users, but there may be new folks who can benefit from knowing the relationship base FPS and ATW FPS have with each other.

 

Asynchronous Time Warp, or "ATW" is the manner at which the Oculus runtime environment attempts to keep the VR device's frame rates at the refresh rate of 90hz (FPS) so that "judder" is avoided to the best degree possible (the DK2 refresh rate is 75hz). ATW frame rates will stay at 90/75 likely all the time.

 

The "Simulation Base Frame Rate", or "sbFPS" is the actual rate at which your sim is running, and that number will never go above 90FPS for the reason that it's locked by the implementation of VR compatibility by the developers. The goal is to keep your sbFPS as close to or at your ATW frame rate of 90fps. Your DCS FPS meter will give you the sbFPS in real time.

 

Hardware controls this relationship. And the more capable hardware you have running your sim, the better your VR experience will be. The reason is that capable hardware will keep your sbFPS as close to your ATW frame rates all or most of the time; the relationship is proportional, and the more powerful your PC the higher your frames.

 

The first sign of incapable hardware is the evidence of "ghosting". Ghosting is the appearance of fuzzy objects like buildings, other planes, objects, etc. You can witness this by watching your frame rate counter and moving your head rapidly. You want to avoid this scenario as the results of this can be VR induced disorientation, dizziness, nausea, or, in the worst case, possible epileptic like symptoms.

 

I've personally found on my own PC with the CV1 that the combination of the 5930 paired with the 980ti gives me sbFPS of 90 most of the time (more tests are needed in some specific areas), but there are some intense areas where frame rates dip noticeably. I'm reading on the various forums that the 5930/5820/6700/4790 CPU comboed with the 980ti is the way to go for VR, and we are considering building a 6700/1080-or980ti machine for testing purposes.

 

The need for good hardware can't be understated in the "VR Age". Since we're really rendering 2+ frames for every one frame of sbFPS, a stout pc is advisable. Knowing the relationship between ATW and your simulation base frame rates can help with ensuring your PC upgrades net you the best gain for the best VR experience you deserve.

 

Happy flying!

 

BoxxMann :pilotfly:

 

NB: It's not my intention to launch a debate about this and that. This is for informational purposes if you are interested in it.

[Ratcatcher]

Hi friends,

Happy flying!

 

BoxxMann :pilotfly:

 

Many thanks for taking the time to explain this. Very useful. I have a new PC on order and hope to see more constantly higher FPS.

 

As is though my experiences are mostly positive, VR is an amazing addition to the flight sim genre and I look forward to the future!

[vicx]

Is there reason you don't recommend the 1080?

[DerekSpeare]

Many thanks for taking the time to explain this. Very useful. I have a new PC on order and hope to see more constantly higher FPS.

 

As is though my experiences are mostly positive, VR is an amazing addition to the flight sim genre and I look forward to the future!

 

VR and flight sims are a perfect fit, something that's been needed for decades.

 

Is there reason you don't recommend the 1080?

 

ED doesn't have the VR features specific to the 1080 video card enabled and and maybe they never will. The 980ti's are dirt cheap now, and they are nearly as power as the 1080's. For over 200 bucks less you can get a video card that does the job and does it well. It boils down to best performance for dollar spent, in my opinion; e.g.:

 

http://www.videocardbenchmark.net/high_end_gpus.html

 

1080 = 18.22 passmarks per dollar

980ti = 27.46 passmarks per dollar

 

Moreoever, I've read nothing that leads me to believe that the 1080 offers significant speed benefits over the 980ti when it comes to DCS (or other titles like FSX:FI, P3D:FI, iRacing, Assetto Corsa, etc.). While the card is more powerful than the 980ti by some, it's really the VR features that make this card (and its progeny) the eventual winner, but since ED doesn't use these features, it is a waste of precious resources right now. Perhaps by the time a hypothetical 1180ti comes out, the developers will be taking advantage of the VR features it will likely have.

 

Ultimately, if a guy wanted simply the most maximum performance possible, then a 1080+4790k would be the top dog. The 1080 is the most powerful video card, and the 4790k is the CPU that offers the highest single core performance available. If one is after the most "thrust to weight" ratio, that's the ticket.

 

https://www.cpubenchmark.net/singleThread.html

Edited August 1, 2016 by DerekSpeare

[hansangb]

Is there a memory difference between the two GPUs? I thought there was, no?

 

And doesn't 1080 have a faster bus/memory? I guess one would have to throw that into the ROI equation.

[twobells]

Great OP, thanks so much, however, in reference to the 1080:

 

When my Rift first arrived I had my GTX970 installed, with DCS options set to 4K, a pixel density of 1.8 and everything maxed out except 'vertical sync' my frame counter recorded a rate of an average 28 FPS. However, when my Gainward 1080 arrived the framerate more than doubled. On average now I get approximately, 48-50 FPS.

In closing, I do expect ED to implement the GTX1080 features, sooner rather than later.

Edited August 2, 2016 by twobells