Performance (Frame Rates) and Anatomical Biology

[NM5K 1]

To me, straight line flight is not really too critical.If I'm doing 30 fps, I'm perfectly fine, and can actually hang with 20-25 in most cases. To me, having the overhead is what really counts.So being able to do 60-70 in easy flight is a good bit better.Not because it looks so much smoother in straight flight,but when making turns, taxing, etc it can really help tohave the overhead so in the bad spots, you can still do atleast 20-25 or so. Another thing about a really high frame rate is the illusionof wind, and the way it looks and "feels" is more realistic to meif the frame rate can remain high.The side to side motion and bounces are more fluid.I only need about 20 fps to make a "greaser" landing with a jet in FSX. Many large airports give me less than that, and I still manage to make decent landings. But I need at least 20+ to really have it feel smooth enough to nothave perceived delays in what the aircraft is doing vs my inputs,and also have the touchdown feel nice and smooth with no clips.Of course, 30+ is that much better.. And 50+ is where I really start to notice the effects of wind, etc start to really feel andlook pretty realistic as it's more fluid.

[january 19]

Just to throw another carrot into the stew-The number of retinal receptors in our eyes is fixed. Consequently, we perceive more image detail when our eyes concentrate on a small area. Often referred to as squinting- as in a single monitor 45

[Guest T-41C]

You seem to mix up 2 different issues here: Frame rates and latency.Latency (also sometimes called throughput delay) is the time between an input the user makes (usually measured at the primary flight controls e.g. stick) to the last pixel being drawn of the first image that reflects the system's reaction to the user input.This latency has to be below certain values to avoid PIO and other ill effects. Though some regulations allow as much as 150ms (or even 300ms for less sophisticated devices) in addition to whatever the actual delay in the simulated aircraft is, I think anything above 100ms can be perceived.Now, a completely different issue is frame rates (i.o.w. how many new images are rendered and displayed (in the professional world the display systems and the image generators are usually synched) in a given amount of time). All professional synthetic training devices of the highest level have to produce at least 60 images per second.Motion simulated by displaying static images at this rate is perceived as fluid under most circumstances by most people. Nevertheless, depending on the scenario and the sensitivity of indivduals, higher rates may be required to completely avoid any perception of non-fluid motion.Also, there is a third issue not mentioned yet: smearing (even at 60 Hz an easily perceivable issue). Conventional displays (e.g. CRTs) and some modern scanline based systems (laser projectors) draw a picture line per line. The time that one particular line is visible is only a fraction of the time that it takes to draw a full image. It will be dark long before this particular line is drawn again as part of the next image. Our brain likes this and easily interpolates between 2 succeeding images. With other projection systems (e.g. LCOS, LCD), one full static image is shown for 16ms and then switched to another static image with no dark time in between. This is problematic as our brain can not interpolate between the 2 images. To avoid this you need to either render and project at even higher rates or artificially introduce a black frame between 2 images, usually implemented via mechanical shutters.

[Illegitimi non carborundum 4]

One question that bothers me and I wonder if the experts can answer: What does FSX actually do when you set the frame rates within the settings to say 30 or even unlimited? Further . . . . At a setting of 30 is the sim actually sending or trying to send 30 frames per second to the monitor? What happens program and visual wise if FSX cannot send the supposed 30 frames?At "unlimited" how many frames are actually being sent to the monitor and what is that dependant on, ie cpu, ram, etc. And now to the biggie - what is the "optimum" frame rate setting in FSX that we should use? Is it a multiple of 24, 25, 60 or whatever?Aplogies, if these are very basic questions.Peter Hayes

[spesimen 135]

>One question that bothers me and I wonder if the experts can>answer: What does FSX actually do when you set the frame>rates within the settings to say 30 or even unlimited? i'm hardly an expert..but here's .02.. i think one of the phil taylor blogs (or maybe some nick n post) discussed this in detail, but if i recall correctly, the idea is if you set a fixed rate, whenever the simulation gets ahead of that speed it will use the extra time in that frame to get caught up on loading more texture details or terrain details rather than starting to render the next frame right away. at unlimited it prioritizes framerate over everything.>Further . . . . >At a setting of 30 is the sim actually sending or trying to>send 30 frames per second to the monitor? yes, in that case if it finds that a frame is done rendering faster than 1/30th of a second, instead of starting the next frame it will do other housekeeping tasks or grab some more higher-res textures etc. this can result in helping with 'blurries' or whatever. >What happens program and visual wise if FSX cannot send the>supposed 30 frames?then it's playing catch up and basically isn't acting much differently than if it's at unlimited but running slow due to whatever factors (detailed plane, lots of clouds or scenery or ai etc.)>At "unlimited" how many frames are actually being sent to the>monitor and what is that dependant on, ie cpu, ram, etc. up to a point it is limited by video card, but with anything 512mb+ like an 8800gt or better it is starting to get limited by cpu speed. when i overclocked my cpu by 10% i actually saw a pretty much linear 9-10% increase in framerate. if your videocard is relatively good it's not so much of a bottleneck although this can be affected by running very high quality aa settings and high resolutions together except on the most top end stuff.>And now to the biggie - what is the "optimum" frame rate>setting in FSX that we should use? Is it a multiple of 24, 25,>60 or whatever?basically it's up to you which feels better when you fly it, although i think you might say instead of 60 to set to the refresh rate for your monitor. the issue gets more complicated because for some people (myself at least) using a fixed framerate results in an overall reduction in average framerate. it also depends on what kinds of mods you are using and many other factors. there's no harm in just trying out different settings, although i think you'll find most people run something like 20-25 to prioritize appearance and smoothness, or unlimited for raw performance.. it also depends i'm sure on settings in your .cfg files..>Aplogies, if these are very basic questions.>Peter Hayesand apologies if my answers are off base at all. i was very interested in this thread because i have always been intrigued by the issue of how motion blur due to receptors (or film emulsion for that matter) being exposed over time affects your perception..different than discrete images like a video simulation is rendering... one thing not really mentioned is also that the physics simulation and your inputs to it seem smoother at higher framerates - i don't know how fsx does it but some engines calculate at a fixed delta and others by frame, which can lead to things like stuff snapping around on a slow frame because it extrapolates further than was expected without enough damping, (like flying with 2x or 4x time)but even with fixed intervals for physics, if your view of what is happening is across variable time intervals your ability to react is messed up.. back in 99 or so i read a study done by the military in sims where they examined the ability of pilots to react at different framerates and determined that the 60-75 range was where it stopped making as much of a difference, but anything lower than that was perceptible. that certainly bears out my personal experience with fps games and the like where if i don't have my mouselook locked at 60 i get dizzy or frustrated.. with fsx it's a little more forgiving since you aren't snapping your view 180degrees to watch your six of course, but if this was a combat sim that would be another story too lol.. i can certainly say i would rather run fsx at 60 if i could heh..cheers,-andy crosby

[Illegitimi non carborundum 4]

CrosbyMagnificent answer - made the whole scenario much clearer. I just had to wonder why Microsoft would place a frame counter (as do other games) amd a method of changing those apparent displayed frames in FSX, when it possibly had nothing to do with the way that human beings see images being displayed on digital (and analog) visual display media ie monitors.Now my dog says he gets 400 fps in FSX no matter where he is flying. Woof! Woof!Peter Hayes

[michal 44]

>just had to wonder why Microsoft would place a frame counter> as do other games) amd a method of changing those apparentBecause FPS is what people know about it, what an average person understands.The only way to do it 'right' would be to dump statistics to some flat file (say every 5 minutes) that would give you comprehensive histogram of all frames that arrived during this 5 mins, grouped by intervals between them. Say there 500 frames separated by 1/25 sec, 400 frames by 1/10 sec, etc. This type of comprehensive data could give you high level picture and true understanding what is going on in the fluidity department.Michael J.http://img142.imageshack.us/img142/9320/apollo17vf7.jpg

[Illegitimi non carborundum 4]

MichaelGood point, I knew that it had to have some validity.Peter Hayes

[tfm 169]

I think I read somewhere on Avsim a post by someone who works for a company building proper full-motion flight simulators. I think he said that the stuff they use delivers 60fps and they won't settle for anything less.That is consistent with the impression I received on a British Airways full-motion 737 simulator last year. The graphics were very primitive, but the smoothness & fluidity were so great that overall the experience felt very convincing indeed (though I guess the full motion and the proper controls helped too, obviously!). I remember estimating that the framerate must have been 50fps or higher and I tried it out back at home on FSX by reducing all my settings and landing at simple airports etc. Sure enough, I found there was a world of difference between an approach at ~60fps and an approach at ~25fps or even ~30fps: the ground just comes towards you much more alarmingly.Tim

[january 19]

-----"Sure enough, I found there was a world of difference between an approach at ~60fps and an approach at ~25fps or even ~30fps: the ground just comes towards you much more alarmingly."--------------Tim- If one has to choose between fps or a wider Field of View- I choose the latter without hesitation. For an experiment, I just took off in my triple monitor setup- 150

[tfm 169]

Good point. Maybe high framerates are only a poor substitute for a wide field of vision which, of course, is something else you get buckets of in a full-motion sim. Your screenshot certainly makes it look tempting.However, my wife is already on the verge of taking a hammer to all my flight sim stuff. I don't think coming home with another 2 monitors would improve her feelings towards FSX.Still ...Tim

[greggerm 312]

Quit giving me more reasons for investing in a TH2G system!! Darnit!:)-Greg