Pimax VR: What is the trick to using lower FPS rates smoothly?

[Dangerzone]

Hi,

I’ve noticed some people running VR at frame rates lower than their headset’s native refresh rate.

Back when I used the HP Reverb (60/90Hz) with a 2080S, I could get smooth performance at 30 or 45 FPS using SteamVR and motion reprojection. The key was running at a clean divisor of the headset refresh rate (e.g., 90Hz → 45 or 30 FPS). I couldn't get anything smooth however with not clean divisors. (ie, 55fps on 60hz). 

Now, with my Pimax (lowest refresh rate 72Hz) and newer hardware, I’m seeing people talk about lower-than-native fps. For instance, @Calvin.Pimax mentioned to expect 65-70fps on a 5090 (which is less than the slowest native refresh rate of the headset). 

I'm sitting here going "BUT HOW?" (Like MOSS in the IT crowd) 

If I run less than 72fps (say at 65 as mentioned) - I get poor frame pacing. It's jittery and would definitely cause me motion sickness after a while. I need to hit the headset’s full refresh rate. Anything lower - especially if it’s not a divisor like in the above example - looks jerky. Yet, I keep hearing users talk about flying with 50–55 FPS. (Non-divisor fresh rates). How is that possible? How can VR stay smooth at non-divisor frame rates?

I thought maybe they're using 'motion smoothing' to fill in the gaps, but when I use it - it's still a jittery mess for me. 

Is there a setting, tweak, or technique I need to use in order to use lower than native refresh look smooth in VR? I can't help but think I'm missing something really basic. 

For now, I'm able to maintain 72FPS (just) with my setup with numerous compromises, but that's with relatively basic missions, but I'd love to know how people are having success with less than 72FPS.

[Peedee]

7 hours ago, Dangerzone said:

Hi,

I’ve noticed some people running VR at frame rates lower than their headset’s native refresh rate.

Back when I used the HP Reverb (60/90Hz) with a 2080S, I could get smooth performance at 30 or 45 FPS using SteamVR and motion reprojection. The key was running at a clean divisor of the headset refresh rate (e.g., 90Hz → 45 or 30 FPS). I couldn't get anything smooth however with not clean divisors. (ie, 55fps on 60hz). 

Now, with my Pimax (lowest refresh rate 72Hz) and newer hardware, I’m seeing people talk about lower-than-native fps. For instance, @Calvin.Pimax mentioned to expect 65-70fps on a 5090 (which is less than the slowest native refresh rate of the headset). 

I'm sitting here going "BUT HOW?" (Like MOSS in the IT crowd) 

If I run less than 72fps (say at 65 as mentioned) - I get poor frame pacing. It's jittery and would definitely cause me motion sickness after a while. I need to hit the headset’s full refresh rate. Anything lower - especially if it’s not a divisor like in the above example - looks jerky. Yet, I keep hearing users talk about flying with 50–55 FPS. (Non-divisor fresh rates). How is that possible? How can VR stay smooth at non-divisor frame rates?

I thought maybe they're using 'motion smoothing' to fill in the gaps, but when I use it - it's still a jittery mess for me. 

Is there a setting, tweak, or technique I need to use in order to use lower than native refresh look smooth in VR? I can't help but think I'm missing something really basic. 

For now, I'm able to maintain 72FPS (just) with my setup with numerous compromises, but that's with relatively basic missions, but I'd love to know how people are having success with less than 72FPS.

Calvin’s reply was for the Crystal Super running in high resolution and in TAA. That means rendering in crazy high resolution for each eye. 
 

Using DLSS 4 or lowering the resolution just a bit should get you over 72 fps. And then you can run the headset at 72 fps and get it smooth. Even with lowering the rendering resolution on the Crystal super a bit you would still enjoy the fantastic pixel density of the Crystal Super and the great field of view. I can’t stand jittery and stutters in VR either.  

[Dangerzone]

50 minutes ago, Peedee said:

Calvin’s reply was for the Crystal Super running in high resolution and in TAA. That means rendering in crazy high resolution for each eye. 

Thanks. That explains the reason why I can get 72fps, and the expectation of the super is that it won't get that high with a 5090 - but at the same time, I'm still wondering how people are surviving in VR with less than refresh rate FPS's.  Are people really putting up with the jitters that come with running less than that (for those who can't reach 72fps), or is there something basic that I'm missing that allows a lower FPS to work fine with higher refresh hz VR?

As mentioned - I was able to run 36fps back 'in the day' with SteamVR and it was quite good on the HP Reverb. Seems that since OpenXR I haven't been able to achieve the same level of smoothness without reaching a min FPS that matches the Hz, so just wondering what I'm missing with OpenXR, etc.

[miguelaco]

I concur with your observations. Anything below headset's native refresh rate seems jittery and definitely not a good experience. I also wonder how people cope with these situations and even say they're happy to have such a "high" refresh rate. I also thought if there is some magic or trick I am not aware of to get good results when fps go down below native's.

Edited Thursday at 04:56 PM by miguelaco

[Dangerzone]

11 hours ago, miguelaco said:

I concur with your observations. Anything below headset's native refresh rate seems jittery and definitely not a good experience. I also wonder how people cope with these situations and even say they're happy to have such a "high" refresh rate. I also thought if there is some magic or trick I am not aware of to get good results when fps go down below native's.

Thanks. I'm glad to know I'm not the only one / not going mad. 

I'm still suspicious that ther is some setting that I'm missing, or some trick but for me - if my PC can't keep up with the native fresh rate and drops behind - it gives jerkiness that I can't contend with. Hopefully those that are happy with sub-refresh rates will be able to chime in.

[miguelaco]

What really puzzles me more about this subject is realizing that some people prefer to run the headset at 90Hz,which means it's more likely to have drops below the native rate. Having quite a hefty system myself (i9 14900K + 64Gb + RTX 4090) I find it simply it's not possible to run the sim at 72 fps in all situations. There are instances, for example, while flying low over highly populated areas in some maps, I struggle to reach the required rate for smooth flying. Maybe lowering details or reducing the headset's pixel density would alleviate things a bit, but I'm quite skeptical it's worth it at all. What do you think, is 72Hz the way to go or 90 Hz with less detail is worth it?

Edited yesterday at 11:25 AM by miguelaco