Smooth and No Stutters - suggested solution

[Peter Dooley]

This issue has been talked about for years and has frustrated all of us.

Instead of trying to fix the problem with higher and higher frame rates, I suggest that LM look into the slow "draw rate" (refresh rate) that limits scenery AND gauge refresh updates to 18FPS (the old tick 18 problem )

Frame rate must not be confused with refresh rate.

To illustrate this refresh rate limitation, simply fly any aircraft that can climb at more than 10,000 FPM (usually any military jet) and set your scenery sliders to a value that gives you a frame rate greater than 25FPS ( I usually do this test at around 100FPS)
Then look closely at the Altimeter needle (or any other fast moving needle) and you will notice that it is not smooth and appears to stutter, just like the scenery does. This appears to be caused by the slow draw rate limitation (refresh rate) of 18FPS. Then fly low level and look closely at your scenery and you will notice that the scenery is also not smooth and appears to stutter at the same slow refresh rate as the gauges do.

So in my opinion, if the draw rate ( refresh rate ) of the scenery and gauges is increased marginally from 18FPS to 25FPS, we will all have smooth and stutter free graphics when our graphic settings allow a frame rate of 25FPS or higher.

I therefore again request that LM investigate this and I sincerely hope that this post will help in solving this age old problem.

Kind regards

Peter

[Kosta]

So you mean, although PMDG and FSL allow the refresh rate of their gauges to be set to 30fps, and nominally at 20fps, that these fps are actually not maintained, am I understanding this correctly?

[Peter Dooley]

Yes, that is exactly what I am saying.

Furthermore, remember also that a standard monitor can only refresh at 60Hz so even if LM were able to increase their draw refresh rate to lets say to a whopping 100FPS, the monitor would then become the new limiting factor but that is not the case here. For that reason, when I fly normally, I always limit the FPS to 60 because a value higher than that wastes my other hardware resources but I do not intend confusing this post with monitor refresh rate discussions as they are currently not applicable to the problem.

I am also a great fan of PMDG and others and have a great respect for them so this response is in no way intended to speak badly of anyone. If however they have another good reason why they allow this setting, it would be interesting to hear from them too.

[downscc]

Many of us have gone to 20 fps frame rate lock and 4K monitor or TV at 30 Hz. Works amazingly well. Try it. Some may bump the lock to 24 but 20 works for most.

[Kosta]

20fps... ugh. Ugly, really ugly. Anything below 30 is for me a slideshow, even 25. I see difference clear as day. And my monitor can also do 30hz without problem.
For me 30fps is a big compromise. Did some flying at 60fps, with Majestic Dash, and wow... talking about reality.

On the topic of gauges, well I never really investigated it, but I'll go with this one: gauges have never been for me something great in FS. Yes, they work, are mostly smooth, but they could definitely be smoother.

So, one thumbs up to fix this.

[Peter Dooley]

Thanks Kosta.

Generally, the human eye can only detect flicker below 25FPS which is why the old movies were mostly filmed at that rate. So setting a value below that will usually always result in the user being able to detect some flicker (stuttering as I call it)
Conversely, anything above that is essentially wasted except that I like to limit my frame rate to 60FPS to smooth out any sync errors (eliminates the old wagon wheel turning backwards effect in the old movies)

I will do some more tests and post the results later for those who are interested.

[105OE]

Anything below 60fps is not acceptable when doing any faster maneuvering than required during smooth, low bank angle IFR flying.
That's where 30fps is sufficient IMO.
The gauge refresh rate was never a problem but e.g. the way too jerky and jumping needles due to the way too low resolution is when performing e.g. an ILS approach.
Makes precise GS/LOC control much more difficult than necessary. X-plane and Aerofly FS2 e.g. have totally smooth navigation instruments.

[Kosta]

I don't know why it's always said that human eye cannot see a difference about 25 and 60 fps, yet I see a very distinctive difference between 30 and 60 fps, even if my FPS is very very smooth, for instance monitor running at 30 and 60 fps for these test.
The reaction of the sim is completely different, the sim is smoother, the response of controls (or actually the display of that) way faster and precise... for me, landing in MJ Q400 at 60fps is a way better experience than doing the same at 30fps!
And before anyone asks, I would bet a lot, that I could differ these two without knowing which is which.

[105OE]

I completely agree. That's why I wrote 30fps for IFR type flying is 'sufficient'.
60fps definitely offers the smoothest flying experience this high frame rate is difficult to achieve in P3D/FSX.

[Kosta]

Yes, but also in IFR you need visual of the runway, especially in flare, and this is where 60fps behaves completely different.
It's doable with 30fps, but for me, anything less, especially 20-25fps, and my landings suffer greatly.

But as you say, even maintaining 30fps is a real challenge in P3D. And it most likely will never change.

[105OE]

Didn't notice substantial differences (if any) between 30 and 60 during the flare but I don't have the Dash 8 and maybe their 'external' FDE is heavily frame rate dependent ? (like x-plane)
20-25 is definitely too low for precise & smooth maneuvering.

[Peter Dooley]

I have done some more tests and can confirm that the maximum update rate is 18 per second and it appears that this applies to the entire scene, that is, the gauges and the scenery.

That means that if your simulation software is updating the scene at 18Hz and your frame rate is lets say 36Fps then your graphics card is rendering each simulation scene update twice before it is updated. If however you have a frame rate of 54Fps, then the graphics card is rendering each scene update three times. In other words, the same scene three times before the next scene update

However, if your hardware is only capable of lets say 9Fps, then every second scene update is missed and this will most certainly appear to stutter.

The problem arises where the scene update and the frame rate momentarily go out of sync as would be the case if you had both a graphics card frame rate of 18 (or thereabouts) and a simulation scene update rate of 18. So to keep it all smooth, we set a graphics card frame rate to at least double the 18Hz scene update so that if the graphics card misses a scene update due to a timing sync mismatch at any point, it can catch the updated scene on the second round before the simulation software updates the next scene.

If anyone requires my test procedure, I will be happy to post details.

[Peter Dooley]

The bottom line is that the current simulation scene update rate of 18 per second is simply too slow. We need at least 25 per second (or better) to get past the flicker threshold of what the human eye can detect (25Hz)

I certainly hope that LM can fix this problem and make stutters a thing of the past.

[Martyson]

The bottom line is that the current simulation scene update rate of 18 per second is simply too slow. We need at least 25 per second (or better) to get past the flicker threshold of what the human eye can detect (25Hz)

I certainly hope that LM can fix this problem and make stutters a thing of the past.

Would the P3D fix for [slow "draw rate" (refresh rate)] need to take into account users:
Which CPU, OS, graphics card, payware scenery, number of monitors, monitor type, SLI, P3D settings, Nvidia profile settings are in use?

I use Target FPS = 20 and all my gauges are smooth for the aircraft / flights I do.
If I set Target FPS to 60 all is ok also but the FPS counter drops to 40 .. no harm .. my system just cannot do 60 FPS in FSX, P3D or Xplane.

[105OE]

Which plane in P3D has smooth LOC/GS indications if I may ask?