ATI R300 : Vibrating / Blur effect with Vsync - low fps

[THe_KELRaTH]

Ever since I installed a 9700Pro some 5 months ago I've had areas of games that stutter quite noticably. I eventually isolated it to having Vsync on and fps below the vsync cap.

I recently posted this on Rage3D:
To replicate the stuttering effect all you do is set the Display / monitor refresh Hz rate above the fps rate and lock Vsync on. In any game if the fps is the same or would be higher if Vsync were off then games are smooth / fluid but when the fps drops below the display Hz you get stuttering - this can be in long or short intervals (like motion blur) and seems to being caused by the card stalling due to a collision between the graphics memory updating and the display refreshing.
To demonstate the problem clearly it's easiest to use a lower spec CPU like 1 - 1.8Ghz (so your fps isn't too high all the time), run a game like UT2003, set monitor refresh at 60Hz and set Vsync on. Using a map like DM-Antalus, pan / strafe the trees and rocks and notice how when your fps is above 60Hz it's perfectly fluid but when fps drops below 60 you will see a motion blur / rubber band.
I have gone back to the earliest drivers, that could be altered to set vsync on via registry, and all show the same problem.

Sireric (ATI) replied:

Ok, the QA guys tried to replicate this and then came to get me to try to reproduce it. Here are the two systems we tried:

P4 1.7 GHz, i850, 512MB, SB Audigy, NIC, 9700P

Athlon 1400, KT266A, 512MB, SB Audigy, NIC, 9500

With both, we ran DM-Antalus in "instant action" mode. Using latest Demo of UT2003. Ran at:

1024x768, noAA, noAF
1024x768, 4xAA, 8xAF
1280x1024, no AA, noAF
1280x1024, 4xAA, 8xAF

tried with our latest drivers (9700p) as well as Cat 3.0a (9500) (7.81, downloaded from the net yesterday).

We set the refresh to 60 Hz, VSYNC forced on always. With the 9700pro, we saw no stuttering and the whole thing was very clean and smooth.

With the 9500, with AA on, there was a few stuttering items noticed, but straffing the trees/rocks, etc... there was no rubber banding or really any lack of smoothness. Overall, we each played 10 minutes on both system, and it looked really smooth.

Can you try the following items:
1) Set AGP aperture to 64MB
2) Disable all sound, disable all background apps and run with a clean boot.

Can you see if there's anything that causes an improvement difference?

My response:
Hi there Sireric, appreciate your time on this.

My AGP was already set at 64MB but I tried 32MB just in case and I've removed the Audigy sound card and drivers.

I've got to say I only used 60Hz as an example. With UT2003 Demo it's half the polygon count of the retail version so your fps will be much higher. (Mine was about double!)

The key to the problem is when your fps drops even 1 fps below your display Hz setting - it's an on/off effect not a gradual either. In console (~) type Stat fps to get the fps up or use fraps (www.fraps.com).

If my fps is above or at 60fps with 60Hz set it's absolutely fluid but as soon as it drops below this, thats when I see this vibrating / motion blur type of effect.
I can strafe along the rocks and as my fps goes above and below the display Hz setting I can watch the vibrating effect go on and off.
I've now tried with Vsync off but used triplebuiffering but unless I can get the fps almost matching the Display Hz there's serious tearing.
I can't remember id the demo had triplebuffering option or not but as with all demo options it has to be done but editing the ut2003.ini file under
[D3DDrv.D3DRenderDevice]
UseTripleBuffering=True

The tests have been done on an Asus CUSL2 Intel 815e chipset with P3-1Ghz 512mb ram - even installed an older Bios just in case, and an Asus P4T533-R 850e with P4-2.53 512mb PC1066 32bit Rdram.
The CUSL2 has Win2k Sp3 while the P4T533R has XP Pro.
Both 9700Pro's are Ver 1.1 - Dx9 Final with Cat3a.
Also tried DVI port - just in case!
Both PC's have been striped down to basic components with fresh installs. I think I mentioned earlier that I've also tried a full range of drivers starting with the one's on the CD.
Neither PC is having problems with any game glitches - even RalliSport is running fine. The problem doesn't seem to game related. For these tests I've been using RTCW openGL, UT2003 D3D and UT1 openGL and D3D.
UT2003 Antalus map - point of test reference
...........................................

On another point regarding D3D settings requiring a reboot:
Both PC's suffer from this since using the CAT3 Final drivers but the compatibility settings can be altered immediately and I've just tried RageTweak 3.7 and that alters AA/AF immediately.
................

The question is.. is it just me (and a few others) or is this the cause of the many posts complaining of stuttering and mouse lag.
It would be really useful if other users with R300 based cards could test this theory out too or suggest another reason that this happens.

Cheers Kel

[Joe DeFuria]

Seems to me the characteristic you described is just the natural phenomenon of v-sync, and nothing to do with the card.

You SHOULD notice "stuttering" (uneven frame rate) when the fps drops below the refresh rate. And it will indeed be the worst when the FPS is just below the refresh rate.

The only solution is to either raise the FPS (lower resoplution, turn down AA, get a faster CPU), or lower the monitor refresh rate.

Or, you turn v-sync off, and it will be smooth...but of course you have to deal with the tearing.

[Mize]

Seems to me the characteristic you described is just the natural phenomenon of v-sync, and nothing to do with the card.

You SHOULD notice "stuttering" (uneven frame rate) when the fps drops below the refresh rate. And it will indeed be the worst when the FPS is just below the refresh rate.

The only solution is to either raise the FPS (lower resoplution, turn down AA, get a faster CPU), or lower the monitor refresh rate.

Or, you turn v-sync off, and it will be smooth...but of course you have to deal with the tearing.

Joe is absolutely correct: the perceived frequency when two are mixed is termed the "beat frequency" and is equal to the difference in frequencies - the closer they are the lower the frequency.

Mize

[THe_KELRaTH]

I could understand that there might a a small amount if for instance you have display Hz at 60 and your fps is going a bit below and above as then it's really switching from 60 to 30 but this happens even when fps shows as a constant 35fps therefore there shouldnt be any vibrating effect as it's really running just at 30.
I've never seen this effect before and I've had 3D cards since Voodoo 1

[OpenGL guy]

Here's a good test reference point:
http://upload.ipaska.net/012003/UT2003-Antalus.jpg
I don't understand the relevance as the image is updating without respect to vsync.

[Mize]

Here's a good test reference point:
http://upload.ipaska.net/012003/UT2003-Antalus.jpg
I don't understand the relevance as the image is updating without respect to vsync.


Me neither, but it sure hurts my brain.

Mize

[Joe DeFuria]

I could understand that there might a a small amount if for instance you have display Hz at 60 and your fps is going a bit below and above as then it's really switching from 60 to 30 but this happens even when fps shows as a constant 35fps therefore there shouldnt be any vibrating effect as it's really running just at 30.

That's not correct. You will get inconsistent frame rates any time your actual frame rate is lower than your monitor refresh rate. If you are at 60 Hz refresh, and your FPS is lower than that, you will be "switching" FPS constantly. If you are between 30 and 60 FPS, your synced frame rate will vary between 60 and 60/2 (30) FPS. If you drop to between 20 and 30 FPS, your syncd frame rate will vary between 20, 30, and 60 FPS. (At least, I believe that's correct.)

Here's an "illustration:"

http://www.sciencejoywagon.com/explrsci/dswmedia/tonebeat.htm

Click on 403 Hz...Imagine that is 60 Hz refresh rate. Now click on 401 Hz. That represents 59 FPS. The rhythmic change in the tone you hear represents the rythmic "changing" of the FPS. Sometimes at 30 FPS, sometimes at 60. Your average will be closer to 60 than 30.

[THe_KELRaTH]

If I strafe left / right across the UT2003 pic using a Ti4200 with Vsync on, Display set at 60Hz (although 75 / 85 makes no difference) the image is quite smooth and the edge of the tree trunk does not vibrate like an elastic band but it does with my 9700Pro.
I bought UT1 when it 1st came out some 3 years ago, back then I had a Rage Fury 32mb - ave fps was about 25 - 45, my display Hz has always been set to 85Hz - it was perfectly fluid. Now, with my 9700Pro my fps is alot higher but the difference I get this vibrating / blurring effect as soon as my fps drops below the Display Hz.

I've been playing games at 30 - 50fps for years and this have never been an issue, I'm sure we're not talking about the same level of problem that I'm experiencing.

Oh.. my pic - I'm seeing something about don't steel bandwith - is that what you guys are seeing - it's meant to be a pic of UT2003 DM-Antalus!
(must be only for use on Rage3D). If so appologies, as the flashing is quite annoying!

[Mize]

I'm convinced that you're seeing something other than the inconsistent fps that Joe is talking about. Is it possible that you have a corrupt drivers installation? I'm not near my machine so I can't test your problem, but I'm just wondering if you might have a driver issue from leftover files from other driver sets or your old detonators...possible?

Mize

[THe_KELRaTH]

Hi Mize.. My detonator drivers left me along while ago - about 5 fresh installs of Win2k ago! :wink: I've also gone right back to the CD drivers (6143), then all the way up to the latest Cat3a. Always the same.
Further there's 2 PC's with 9700Pro's and 1 with Geforce 3, and 1 with GF4 Ti4200. The other PC with 9700Pro is a P4T533R/ P4-2.53 WinXP Pro). The PC's with Geforce cards in are based in Intel 815e chipset with P3-800 and 1Ghz (both Win2K Sp3).

[THe_KELRaTH]

I did some more testing earlier and the vibrating / blurring effect reduced as I lowered the detail settings of the games I tested. In Ut2003, by the time I'd turned off or set to lowest all the video option settings, it was quite smooth at any fps whether 30 or 59.

So, as a summary: with Vsync on with Display at 60Hz I can run the game smooth with fps anywhere between 30 - 59 with low detail OR turn full details at max and get this vibrating effect except when at the same fps as Display Hz.

Just out of curiousity, can anyone tell me why this should happen?
I can understand why loading the card with higher textures etc could cause the vibrating effect but why would getting fps to the same speed as the Display Hz with Vsync On counter this.
What actual components within the card would go out of sync when a higher texture load is put on. Does Vsync syncronize certain parts of the card aswell?

Cheers Kel