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LCD TV's and 50Hz PAL panning problems or not?

Discussion in 'LCD & LED LCD TVs' started by ilrenato, Jul 25, 2005.

  1. ilrenato

    ilrenato
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    Hello,

    Many tests reveal that almost all LCD TV's are 60Hz panels with tuners and scalers that convert to 60Hz.

    So when you watch TV in europe main land, you get PAL 50Hz that gets frame rate converted to 60Hz and then displayed.

    So far every test I have read or LCD I have seen has so much judder or tearing on pans that it renders an LCD unfit in my vision.

    I have a Dell 2405 whith the exact same problem.

    From a technical point of view, I know an LCD can be 50Hz, but the world market seems 80% 60Hz (USA) so most brands don't bother.

    So I have three questions:

    1: Are there real panning tearing trouble free PAL LCD tv's?

    2: If they exist, can it be that there are 50Hz LCD panels?

    3: Would a 50Hz display really flicker?

    Concerning frame rate control, even the most expensive scalers have trouble with 50-60Hz conversion, let alone your "sale!" tv.
     
  2. LV426

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    1: I can't comment on how the image is processed prior to display, but I see no panning judder on my 22 inch Samsung.

    2: ?

    3: LCDs don't flicker at all, regardless of refresh rate
     
  3. David Mackenzie

    David Mackenzie
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    I don't think that's how LCDs work, is it? The panel doesn't have a refresh rate as such - it only updates parts of the screen when they change?

    Have you ever tried it on an LCD TV? If it was on a PC, what DVD player software were you using?

    The problem you're getting there is probably that your computer is outputting 60hz even for PAL (50hz) DVDs. I don't think any computer video card is capable of outputting 50hz. But on a TV, a 50hz signal can be fed in no problem, and as far as I know without conversion.

    I've never noticed anything like this on my own Sony LCD TV and I'm the sort of person that would - but I'll have another look.
     
  4. ilrenato

    ilrenato
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    No, the memory may be partly updated, but every image pixel is scanned and displayed at a regular interval, say, 60Hz?

    Not on a PC, just using internal tuner or a PAL disc in a PAL dvd player.

    No, again no computer. And yes, it can be fed, but does it display in 50Hz?
    I have not seen the very $$ top of LCD's but also tests in for example C't (germany) show again and again, that many LCD's work 60Hz frame rate and inputs get frame rate conversion.

    There are test discs out there with moving objects that allow to trace such ill behaviour.

    In projectors, the synching is quite important so dlp projectors lock to multitudes of 50 or 60 Hz like 300Hz. But LCD's can not.

    Anyone with "digital video essentials" dvd that has tested this at 50Hz and sees perfect image of fluid moving bars?
     
  5. David Mackenzie

    David Mackenzie
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    Thanks for putting me in the right there then, I never knew of this problem. Do you have any examples you could give me of DVDs that would show it up best, or would any camera pan for example do?

    As I said, I use a Sony LCD WEGA myself so I'm curious to see what the result will be. It'd be good if we could get a lot of of people using a wide range of LCDs to post in here as well.

    I've just tested my own Sony KLV26HG2 and from testing a few discs, the panning is perfect on both 576i and 576p.
     
  6. ilrenato

    ilrenato
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    In case you have never noticed, you are best advised not to look for it :)

    Any panning on tv, say tennis, would do, but best is one of the test dvd's commercially available.

    For PAL my reference is www.peterfinzel.de test disc or the notorious Digital Video Essentials 2 (PAL) available thrugh various channels.
     
  7. David Mackenzie

    David Mackenzie
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    I don't have any test discs, but I just tested an animated DVD, no problem there, and also a live action one.
    The credits scene at the start of Pulp Fiction (I own the censored British disc because I have it in a 3-disc box set) makes a good test, when the names of the actors scroll up the screen. No jerking at all on my TV. If I tell my DVD player to convert the image into 480p/60hz (which I'm assuming would give the same results as if the TV were converting itself), jerking is visible. It's fairly uniform though, and would be easy to miss unless you had something to compare it with.

    So yeah - it looks like you helped me answer the question - TVs without the problem do exist. I really should get ahold of a test disc though.
     
  8. monopole

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    Just go to news 24 - the scrolling text at the bottom of the picture should be smooth - if it judders, then your refresh rate is unlikely to be 50Hz.
     
  9. LV426

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    Yes, that's a good test. I guess scrolling titles (eg at the end of a movie) would do it, too.

    No judder on my Samsung, then.
     
  10. kgreene

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    interesting stuff....
    If I am connecting my (yet to be purchased) LCD TV to a media centre PC for watching TV the graphics card on the PC can be set to output at 60Hz to the LCD.
    Does this mean I will NOT have this tearing panning problem or will it still be present as the broadcast TV signal is still at 50Hz so something in my PC is doing the conversion?
    I'm finding this LCD or plasma TV buying experience to be a nightmare! Glad I found out about this though. :smashin: and will probably get one of these test DVDs to take to the shops for test viewing.
    Ken
    BTW Is this why Sharp are talking about PAL optimised LCD TVs being released soon?
     
  11. David Mackenzie

    David Mackenzie
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    Kgreene, I think Sharp's PAL optimization would primarily mean resolution, but it would count for this too I suppose.
     
  12. LV426

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    If you are trying to display a natively 50hz signal (eg PAL TV) at anything other than 50hz or a simple multiple, then a complex frame rate conversion must be happening somewhere. And yes, if your PC's graphics are set to 60hz, then your PC is doing the work. And yes, it may, quite possibly, do it badly. And no, this has nothing at all to do with the monitor in use. Any artefacts thus introduced by the PC will display just as well on a CRT.
     
  13. ianh64

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    The service menu of the Loewe Xelos SL has the following option bytes:

    Byte 5
    #2 (1 on) 50 Hz Progressiv-Darstellung / 50 Hz progressive prepresentation
    #3 (0 off) 60 Hz Progressiv-Darstellung / 60 Hz progressive representation

    Byte 8
    #4 (0 off) 75 Hz Interface-Darstellung / 75 Hz interface representation

    NB. For Xelos A series, the option bytes are completely different and will goose your display if you fiddle with them.

    For Eurospec models, the defaults are in brackets. My interpretation of this is that the internals are driven at 50Hz. Not sure what the 75Hz option is as it is worded differently and is in a different option byte.

    I haven't fiddled with these but the unit is silky smooth with 50Hz DVD's when played at SD resolution. There is a scene in Pirates of the Carribean, about 16 minutes in I think, where the camera pans above the castle. I use this to test for judder even though I have DVE PAL. I have never seen judder in DVE even in the test scenes explicitly testing for this. Input from DVI however does suffer from slight judder on this scene - you only notice it if you are looking for it and I don't think it is the correct frequency for 50Hz->60Hz transcoding. It is odd however since SD-P component and DVI input are from the same DVD player (Meridian G98), the only difference externally is that the DVI output is upscaled. I have never been able to draw the conclusion whether it is a player issue or something different in the processing path of the Xelos.

    The moral of this post is that I believe that the Xelos SL is working at 50Hz but it can be changed to 60Hz in the service menu.

    -Ian
     
  14. Andy3

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    For what it's worth, here are my observations:

    Our little 17" Grundig LCD suffers from 'standards conversion' judder. It drives me potty, as I worked for 20 years in the TV repair trade and I'm very sensitive to things like this :suicide: . Some American shows suffer badly from this effect on camera pans and medium-speed movement, no matter what kind of set you watch them on.
    Our new JVC DS6 does not show this effect. No judder or skipping at all, and sideways scrolling text is as smooth as silk.
     
  15. kgreene

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    Cheers Nigel - very useful to have my suspicions confirmed.
    So when buying a new TV what do you have to look for in the detailed spec sheet to confirm that "the thing works with PAL properly at 50Hz".
    This info isn't the sort of thing they advertise as features I guess so any pointers on the question to ask would be appreciated - or do you just check what scrolling text looks like on News24 and use that or another test?

    Ta
    Ken
     
  16. ianh64

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    One things to add. Most screens accepting native resolution input at anything other than a standard video resolution will only accept it at 60Hz.

    -Ian
     
  17. BryanKitts

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    So have I understood the HTPC situation correctly?
    1. PAL sources should be output from PC to screen at 50Hz to avoid panning judder
    2. a decent spec HTPC should do a better job of upscaling than a TV, so it's better to upscale the source to the screen's native resolution on the PC, but
    3. most screens will not accept native resolution at 50Hz
    i.e. you can't watch a PAL source via an HTPC without compromising (either 60Hz judder or TV-based upscaling)? That would seem a shame.
     
  18. LV426

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    Yep, demo I think..... I don't actually recall seeing any LCD TV doing PAL TV badly (in this respect) on display in stores - and I do look for this type of artefact.
     
  19. kgreene

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    Just a bit!
    As I have my media centre PC coming tomorrow and plan to use it for viewing PAL TV broadcasts on a soon to be bought LCD TV. Will let you know if I find out anything useful (but at this rate it's going to take me months to decide on a LCD screen
    :rolleyes:
     

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