refresh rates and strobing

Discussion in 'Projectors, Screens & Video Processors' started by Mr.D, Sep 3, 2001.

  1. Mr.D

    Mr.D
    Well-known Member

    Joined:
    Jul 14, 2000
    Messages:
    11,167
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    133
    Ratings:
    +1,209
    Ok I've hit on something that doesn't make sense to me and maybe you guys can come up with the answer.

    I look at 24fps material every day at work. As a consequence of this my monitor is set to refresh at 72Hz ( res is 1280x1024) . Now when I view material with pans or other horizontal movement in it deopending on how it was shot there is some strobing but not anything greater than you would see if the film itself is projected ( something borne out by viewing the material when it goes back to film)

    However when I watch a 525/60 dvd mastered from 24fps material at home on my PC where it is effectively inverse telecined back to 24fps the strobing on pans is very obvious. ( this is at 1024x768 and again at 72Hz refresh)

    If I up the refresh rate to 120Hz the strobing becomes more like what I'd expect on film material ie visible but not particularly ugly. And additionally more like what I'd expect at work where I use 72Hz.

    disc used for reference was hollow man region1 ( the bit where Kevin Bacon drives into the car park for the first time)

    Questions:

    Why should I get a different result using the higher refresh of 120Hz compared with 72Hz at home. Why should I get similar results to what I see at home using 120Hz to what I get at work at only 72Hz?

    Things to bear in mind at work I have a real 24fps source whereas at home I have dvd inverse telecined to 24fps. This means that the dvd material is actually running at 23.98fps ??? If so why does 120Hz not show a similar result if its as a result of speed mismatch? ( x5 repeat averages out the mismatch better than x3 repeat??)

    My other thought was that the software player ( windvd) was not performing an adequate inverse telecine and I was still seeing a 30fps image with exacerbated deinterlaced 3:2 pulldown and this was visibly improved by going to 120Hz which is a mutliple of 30 as well as 24. However the frame counter is visibly running at 24fps on playback so its not this.

    Reason I'm asking is I doubt there are projectors out there that operate at 120Hz at reasonable resolutions ( certainly not any my missus would not notice hanging from the ceiling). So does selecting the magic refresh rate I see mentioned in other threads (71.94 something I think) solve the strobing? And how hard is it to get a projector to accept this non-standard refresh rate?
     
  2. Jeff

    Jeff
    Well-known Member

    Joined:
    Jul 13, 2000
    Messages:
    5,507
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    106
    Location:
    Basingstoke
    Ratings:
    +263
    Keith,

    The magic number is 71.928, with a bit of work you can get powerstrip to use this magic number. I'm not overly convinced though, unfortunately my Aconda only does 60Hz anyway. The problem with a projector is that many of them don't do a good job at anything other then 50/60Hz anyway. The Rock scaler did very well at the event, its 72Hz is actually the magic 71.928, but it also has extra processing called the Judder terminator to smoothen things out. If you look closely you get what if often refered to as micro judder, you may also get a small jump in movement which is probably some timeing error. When I finally get a projector I will definately have a play, but I might be limited by what the projector can do (specs don't mean jack here).

    Jeff
     
  3. Mr.D

    Mr.D
    Well-known Member

    Joined:
    Jul 14, 2000
    Messages:
    11,167
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    133
    Ratings:
    +1,209
    Thanks Jeff,

    Does this mean that most people with even top notch projectors are watching strobing material ?

    What happens with a 625/50 disc ? Surely if its played in multiples of 25 its an exact match rather than the case with 525/60.

    If so can anyone say for sure that 625/50 material at 75Hz for example doesn't exhibit the strobe on pans to the same extent. If not and this scenario is just as strobey to the same extent as 525/60 material at 72Hz then the strobe seems unlikely to be as a result of the small timing mismatch issue?

    In which case what the bejesus is causing it?
     
  4. JohnAd

    JohnAd
    Member

    Joined:
    Mar 14, 2001
    Messages:
    362
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    18
    Location:
    London
    Ratings:
    +4
    Keith

    Jeff is right when he talks about the correct rate for NTSC film stuff. The fly in the ointment is the sound chip. The was most DVD software players work is to use the DirectShow timing mechanism. This drives the timing off the sound card's timings. I think how it works is that the picture and the sound go there own seperate ways and then there is an adjustment when they go too far out of sync.

    This is the cause of the blips you get even when the refresh rate is correct.

    (What follows is speculation, based on my understanding of DirectShow)

    You're problem seems to be different.

    The other factor here is that the flip timing will only be accurate if you have lots of processor to spare, if you are running on marginal hardware (< 6/700 Mhz) then the flips will just happen when they can and not when they are supposed to. This may look like the stobing you're seeing.

    To get round this you should try and make sure the DVD player is using < 50% CPU (may have to be even lower)

    (end of speclation)

    Things like DScaler can stop the judder only by taking over the whole machine and doing everything themselves. DVD software works in a very different way.

    Hope this helps.

    John
     
  5. Mr.D

    Mr.D
    Well-known Member

    Joined:
    Jul 14, 2000
    Messages:
    11,167
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    133
    Ratings:
    +1,209
    I understand there may well be some governing going on to maintain sync between audio and video paths but this would surely result in the odd pause and stutter here and there. ( see this effect on very early dvd players sometimes)

    The effect I'm referring to is an obvious strobe on medium speed horizontal motion ( pans). If this is down to the slightly less than 24fps of NTSC being viewed at 72Hz instead of the magic number 71.928Hz then viewing a 625/50 film sourced disc that will run at 25fps when deinterlaced at 75Hz should be visibly superior with regard to the strobing? Due to the exact ( I think) 25 relationship?

    I've yet to make my dvd-rom drive region free so could someone with a multiregion drive have a look at some 625/50 material refreshing at 75Hz and comment on the pans please.

    My PC is reasonably well specc'd and I'm pretty sure the strobe isn't down to a lack of resources ( why would it improve at 120Hz) it does look like a presentation issue.

    Really like to get to the bottom of this.
     
  6. Stuart Wright

    Stuart Wright
    AVForums Founder Staff Member

    Joined:
    Jan 24, 2000
    Messages:
    14,602
    Products Owned:
    7
    Products Wanted:
    1
    Trophy Points:
    167
    Location:
    Birmingham, UK
    Ratings:
    +10,467
    Can't answer some of the questions, but if the timing is out and the PC has to skip (or repeat) a frame at 120Hz, then you get that 'error' for 1/120 of a second rather than 1/72 of a second. Hence it looks less severe.
     
  7. JohnAd

    JohnAd
    Member

    Joined:
    Mar 14, 2001
    Messages:
    362
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    18
    Location:
    London
    Ratings:
    +4
    Keith

    Both NTSC and PAL disks run smoothly for me at 72 and 75 respectively. I get occational jumps due to the the resync but overall pans are smooth at these rates.

    Stuart is right that at 120 the errors are better masked but you should not be seeing continuous jumps at 72.

    What is the spec of your machine and how much processor is being used during playback?

    Does this happen with all region 1 films or just hollow man?

    The other usual questions are:

    1) Is there anything else running? Virus, firewall, office, etc<br />2) Are you sharing inturrupts on any key devices<br />3) Is DMA enabled on the DVD drive<br />4) Have you got the latest motherboard firmware<br />5) Have you got the latest graphics card firmware and drivers

    John
     
  8. Stuart Wright

    Stuart Wright
    AVForums Founder Staff Member

    Joined:
    Jan 24, 2000
    Messages:
    14,602
    Products Owned:
    7
    Products Wanted:
    1
    Trophy Points:
    167
    Location:
    Birmingham, UK
    Ratings:
    +10,467
    John, presumably there is a utility to show you how much CPU is used/available? Is there a URL to pick it up?
     
  9. JohnAd

    JohnAd
    Member

    Joined:
    Mar 14, 2001
    Messages:
    362
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    18
    Location:
    London
    Ratings:
    +4
    Sorry, I'm so used to running win2k that I'v forgotten you don't get a CPU tool in windows.

    Get wintop, a quick google search found this site.

    <a href="http://btp1da.phy.uni-bayreuth.de/~ralfp/software/sysutil/wintop.txt" target="_blank">Installation instructions</a>

    <a href="http://www.naples.net/ftparea1/ftp_files/wintop.zip" target="_blank">Wintop Files</a>

    It is part of the free Windows 95 Kernel toys kit and so should be OK to redistribute.

    John

    [ 04-09-2001: Message edited by: JohnAd ]</p>
     
  10. Mr.D

    Mr.D
    Well-known Member

    Joined:
    Jul 14, 2000
    Messages:
    11,167
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    133
    Ratings:
    +1,209
    Thanks John its good to know that this problem can be licked I wouldn't fancy my chances of finding an affordable projector that handled decent resolutions at 120Hz.

    I'm currently configuring my PC as a non-linear editing deck so I've removed all programs surplus to requirements. I'll build another to function as an HTPC in the future.

    Just for the record my PCs specs are:

    Asus A7V Mobo<br />Athlon 900MHz<br />1024M PC133 RAM<br />Soundblaster live <br />Asus V7700 Geforce 2 GTS 32M<br />Memorex Trimaxx whatever DVD/CD-RW combi drive<br />ata100 IBM deskstar 46Gb<br />W2K sp2

    I was using Windvd2000 for playback.<br />Proc usage was averaging 12% on dvd playback<br />ZoneAlarm firewall ( switching off made no difference to playback or proc stats)<br />DMA enabled on secondary IDE port where the dvd drive is . ( shows as DMA when dvd in use)<br />dvdgenie enabling HWMC on card.<br />( using nvidia 6.62 driver for graphics as it performed better than the latest one :3Dbenchmark scores above average for similar spec machines)

    Flashed the Bios on the Mobo a few months ago to the latest version then 1006 I think. Avoided flashing graphics and dvdrom as any info I could find on this applied only to windows 98/ME and certain things are different in W2K. IRQs are assigned automatically also I believe. ( no conflicts in device manager)

    Latest W2K drivers for the soundcard.<br />removed elderly version of adaptec direct CD software that is main culpret for a few BSODs I had ( known problem) : wrongly thought it was WinDVD at first.

    System seems very stable and I can playback a decent amount of 1K res film files ( 1024x778) in other packages. ( better than the SGI Octane I use at work in this respect)

    DVD playback is nice and smooth (occasional pause or stutter no more than once in a 30 min period like your self) Its only when the medium speed pans ( fast and slow ones are fine) come on that the strobe becomes apparent and it does look like a display rate issue rather than the machine running out of steam. Other discs exhibit same effect.

    Normally view dvd in 1024x768 (32bit) squished on display.
     
  11. JohnAd

    JohnAd
    Member

    Joined:
    Mar 14, 2001
    Messages:
    362
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    18
    Location:
    London
    Ratings:
    +4
    Keith

    Have you got the latest version of DirectX and of windows media player installed?

    (just to check that you have the latest version of DirectShow installed)

    John
     
  12. Mr.D

    Mr.D
    Well-known Member

    Joined:
    Jul 14, 2000
    Messages:
    11,167
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    133
    Ratings:
    +1,209
     
  13. JohnAd

    JohnAd
    Member

    Joined:
    Mar 14, 2001
    Messages:
    362
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    18
    Location:
    London
    Ratings:
    +4
    I'll check out some material at the weekend and see if I can replicate what you're seeing.

    Otherwise I'm stumpted...

    John
     
  14. Mr.D

    Mr.D
    Well-known Member

    Joined:
    Jul 14, 2000
    Messages:
    11,167
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    133
    Ratings:
    +1,209
     
  15. JohnAd

    JohnAd
    Member

    Joined:
    Mar 14, 2001
    Messages:
    362
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    18
    Location:
    London
    Ratings:
    +4
    Keith

    Just tried a PAL disk as 75Hz and am getting all sorts of bad panning artefacts. I'll continue to try and work out what is going on.

    It improved slightly when I changed to window mode and usd YXY to size the window rather than using the full screen option.

    But am still getting not very good results.

    John
     
  16. Mr.D

    Mr.D
    Well-known Member

    Joined:
    Jul 14, 2000
    Messages:
    11,167
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    133
    Ratings:
    +1,209
    Nice one John thanks for the info. I'll be reinstalling my machine over the next few days and I'll see if I can look into this further.
     
  17. JohnAd

    JohnAd
    Member

    Joined:
    Mar 14, 2001
    Messages:
    362
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    18
    Location:
    London
    Ratings:
    +4
    Tried playing around some more and couldn't get very good pan's at all with win2k.

    I had a quick play with win98 and that didn't seem any better.

    Just to check I wasn't going mad I ran the same stuff though DScaler with JudderTerminator on and it was lovely and smooth at 75Hz.

    So the probelm isn't in the card rate not being an exact number or anything like that. I'll review all the AVS stuff on judder and see if there is anything obvious we're doing wrong.

    John
     
  18. JohnAd

    JohnAd
    Member

    Joined:
    Mar 14, 2001
    Messages:
    362
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    18
    Location:
    London
    Ratings:
    +4
    I think I've cured it on my machine at least.

    Turning off hardware motion compensation in DVD Genie seems to get rid of the jerkiness.

    Hope this helps...

    John
     
  19. Mr.D

    Mr.D
    Well-known Member

    Joined:
    Jul 14, 2000
    Messages:
    11,167
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    133
    Ratings:
    +1,209
    Hmm interesting I'll leave dvdgenie off the machine when I reinstall windvd .No reason to use it as the drive is region1 in firmware at the moment anyway.
     
  20. Mr.D

    Mr.D
    Well-known Member

    Joined:
    Jul 14, 2000
    Messages:
    11,167
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    133
    Ratings:
    +1,209
     
  21. JohnAd

    JohnAd
    Member

    Joined:
    Mar 14, 2001
    Messages:
    362
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    18
    Location:
    London
    Ratings:
    +4
    Keith

    Motion compensation is an MPEG-2 thing rather than a video thing. It is used to fill the I frames based on the initial frame plus the motion vectors.

    I have a feeling that the video card makers don't run tests with film at 72/75 and so there may be wierd things happening when you do.

    I would guess it works well at 60Hz and possibly at 120Hz as you found.

    Given the low amount of CPU that you use I would guess you do have it switched on. Try turning all hardware acceleration off.

    I also wonder if the fact that it only occurs on medium speed pans means that the motion comp routines get overloaded in some way and stutter. This is sort of what it looks like on my samples.

    John
     
  22. Mr.D

    Mr.D
    Well-known Member

    Joined:
    Jul 14, 2000
    Messages:
    11,167
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    133
    Ratings:
    +1,209
    Thanks John <br />Good info will have a fiddle.
     
  23. Mr.D

    Mr.D
    Well-known Member

    Joined:
    Jul 14, 2000
    Messages:
    11,167
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    133
    Ratings:
    +1,209
    Just reinstalled windvd 2000 ( which is version 2.1).

    Same strobing effect still present at 1024x768 at 72Hz less apparent at 120Hz but I think I can still see it a bit.

    I suspect this is down to the windvd player being a fairly old version: perhaps a newer version will do a better job. I do suspect its a decoding issue. With HWMC switched off( you need dvdGenie to activate it on my geforce2 GTS anyway) cpu usage is averaging about 40% ( highest 68% lowest 20%). I'm also pretty sure the so called brightness slider in Windvd is actually a gamma control rather than a black point control. ( certainly shows up how off the colour temp is across the grayscale on my monitor). Also suspect the whites are a bit on the clippy side although VE test patterns disclose correctly. ( will look into in the future)
     

Share This Page

Loading...
  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice