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"upconversion lag" in HD-ready LCD:s (calling the forum experts!)

Discussion in 'LCD & LED LCD TVs' started by Spokkx, Sep 3, 2005.

  1. Spokkx

    Spokkx
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    here is a quote from an article on upconversion that happens on all "hdtv" (including LCD)

    Indeed. There was a distinct lag between button-press and onscreen-response. In other words, when I pressed the JUMP button, Mario JUMPED about ¼ second later

    since alll new hd-ready lcd:s have 1366x768 resoultion.. upconversion is always necessary in all modes (480i, 480p, 720p etc)

    the processor which does this.. is it usually fast enough?

    I just ordered av Sony klv-S32A10, which I will be using for XB360 gaming in 720p.. do you think the upconversion will make the buttonpresses lag? Lyris or some other expert probably har something to say about this (I hope :)

    or have I got it all wrong? othervise would the inputsignal (VGA or component make any difference?)

    link to the whole article

    http://www.4colorrebellion.com/archives/2005/08/08/the-dirty-little-secret-of-hdtv/
     
  2. David Mackenzie

    David Mackenzie
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    Hey Spokkx, I remember reading that article too.

    On my last year Sony LCD model, there's no lag on any of the modes, and believe me I'd notice. I've heard that the scaling is almost instant, so the only area you can go wrong in is Deinterlacing. But I've never had a problem there either. When I press the Channel Up button on my Freeview decoder the picture cuts to black instantly before finding the next channel.

    If the 2004 Sony LCDs don't have this problem, it's a safe bet your new 2005 one won't have it either.
     
  3. Spokkx

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    sweet, thanks for the answer

    yeah it would be wierd if 2005 model lcd had this problem..
    and I hadn´t heard about this problem at all in flat-screen lcd screens.. DLP:s I knew about..

    buying stuff for this kind of money makes me want to check every everything out..

    especially if it will be for gaming.. wouldn´t be that great if I had button-lag in every game on the x360 (or older consoles for that matter)
     
  4. mince bigalow

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    This guy was talking about a DLP TV, and had no experience with LCDs and plasmas. I reckon he had a duff set. Also there would be no way that Microsoft would use Samsung HDready LCDs in the XBOX 360 demo pods if there was a problem with lag.
     
  5. David Mackenzie

    David Mackenzie
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    He also mentions it was a Samsung DLP. I've never used one of their DLPs (or any DLP for that matter!) but I don't personally have the best opinion of that company.
     
  6. Spokkx

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    ok make me feel really at ease..

    because if there was button-lag on the flatscreen lcd:s there would be an uproar.. though it makes sense that upconversion SHOULD take some milliseconds..
     
  7. jon2099

    jon2099
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    There are 2 places where lag can be introduced- first is the deinterlacing, where the display has to wait for two fields to arrive (sometimes more, say if it wants to detect 3/2 pulldown) before deinterlacing and second is the actual scaling, where it has to wait for the the complete frame to arrive and fill the frame buffer before scaling it to the panel's native resolution. If the display is fed a progressive signal then only the second case applies.

    Compared this to a CRT that does not include any picture processing, where it starts to paint the picture (or scan it) as the video signal arrives.

    Assuming you want to upconvert 576i, then this will be a minimum of a 40ms lag (2 fields). I guess if you want minimum lag, then you use the console in progressive mode as the second delay also applies to PC monitors. In theory this will also affect 1080i, although some panels don't bother deinterlacing and just treats it as a 540p signal.

    I have seen this with a 50Hz CRT and an LCD TV side-by-side being fed with the same signal and the scene changes do always occur later on the LCD.
     
  8. stealth chicken

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  9. David Mackenzie

    David Mackenzie
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    That's not the same kind of lag. The "response time" manufacturers quote is the time the liquid crystal panel takes to react to changes from the video processor in the set. But what we're talking about here is a delay in the time it takes the video processor to finish doing its job and to send its instructions on to the panel.

    (I don't know if this is exactly how the architecture of an LCD TV works, it's just a basic wording to try and explain the difference).
     
  10. Spokkx

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    ah.. intreresting.. exactly what I was looking for..

    so a 360@720p shouldn´t be noticeable.. upconverting shouldnt take that long.. I don´t even notice it when i use my cheap Delll 17" LCD screen in 800x600 (native 1280x1024). we should be talking about.. 10-15ms tops here?

    but for example a gamecube@i576.. 40 ms lag from the deinterlacer? + upconversion.. thats kind of much

    how do you know that every "pass" takes 20 ms? with a fast deinterlacer that could be faster? and upconverting also could be done faster with better hardware? or has this anything to do with that the screen updates 60 times a second?

    please enlighten me :)
     
  11. Caimbeul

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    I have a Samsung SP46L6HX DLP TV and there is most definatley lag (to te point of being unable to play) on UK PS2, Gamecube & Xbox running in standard interlaced modes.

    Also have a Samsung LE26R41BDX in the bedroom. will test one of the console on this and report back.
     
  12. Spokkx

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    oh please do, really interested if the lag is noticeable at all interlaced on a lcd that is hd-ready
     
  13. wush

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    I've noticed absolutely no lag on a Samsung LE26R41B while playing via 480i, 480p, 720p or 1360x768 VGA inputs. :smashin:
     
  14. Spokkx

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    that´s good to hear :)

    but to deinterlace i guess 40 ms really is minimum.. (1 sec / 60 x 2 passes= 33 ms.. add some overhead.. 40ms.. is this right?)

    40 ms may not be really noticable though.. wouldnt know myself as I have not tried a interlaced (576i or such) source on an LCD
     
  15. pjskel

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    Even if it was double that - 80 ms, this is a lot less (1/3) than 1/4 sec (250 ms) as mentioned in the original post.
    So, at a guess I'd say there was nothing to concern yourselves over.
    Certainly, with a DC and Soul Caliber/DOA running into a Sharp GD1 LCD, I've seen nothing noteworthy on this "issue". Even with it's reduced resolution, the DC games were plenty playable and thoroughly enjoyed - been years since I had the DC doing anything but gathering dust. And this was using the SCART, never had need for the VGA cable option.
     
  16. andrewfee

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  17. Spokkx

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    40ms in an online games is noticeable though..(not by THAT much)

    but if the gamers in this forum don´t notice button-lag on and flat LCD in interlaced modes, It cant be really that bad.. more examples anyone?
     
  18. Spokkx

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    of course! why didn´t I think of that.. thanks

    should eliminate any lag the deinterlacer adds (if any)

    edit: but I see this won´t work with PAL Scart-sources.. (the only ones I have on old consoles)

    are there other VGA-adapter/converters?
     
  19. andrewfee

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    The XRGB2+ does work with PAL SCART sources, it's just that most displays won't accept a 50Hz VGA signal.

    If your display will accept it, it'll work. You just have to rewire the SCART cable. I modified a SCART switch block so that I could just plug in regular RGB SCART cables, and it'd output Japanese RGB.

    Even if your set does not have lag, I would recommend buying one, as it improves the image quality for gaming quite a bit too.
     
  20. Spokkx

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    ah.. I doubt my KLV-S32A10 will accept 50hz VGA though..

    may be that input-lag in gaming isn´t really that noticable even through interlaced scart on HD-LCD though.. I sure hope so.. would be a lot less of a hassle for me :)
     
  21. Nic Rhodes

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    Lag is present on all LCDs, due to the reason Jon2099 stated, typical figures will need 40 to 60msec, not a quarter of a second. This will need correcting to sync up the external audio but many processors can do this now. Most notable in lips and speech so may not be too much of an issue for gamers but it will be there.
     
  22. Spokkx

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    for us gamers this stuff is important, every millisecond counts :)

    have I got this right:

    1. upconversion from progressive sources (720p to 1366x768 native display pixel for example) need no deinterlacing. Correct? Therefore you need not wait for 2 full frames. The delay would then be about 16 ms from progressive sources (1 second/60).to receive the whole frame.

    And then some milliseconds to for the processor to transfer the frame from the buffer and display on the screen?

    So about 20ms delay for progressive sources?

    2. And this is the same as the delay you experience on LCD TFT monitors that display pixels that don´t match the native pixelcount fpr the screen. For example display 800x600 on a 1280x1024 sceen?

    If it really is the there really is no problem. Since I can´t se this delay. Have tried it on my 17" LCD Dell monitor..

    Can some expert here confirm if what I state is correct or not?
     
  23. jon2099

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    The deinterlacing lag does depend on whether the source is 50Hz or 60Hz. The 40ms figure I gave was valid for 50Hz sources as it is the time for two fields, for a 60Hz source this is 33.3ms (as spokx pointed out, again this is a minimum figure). This is assuming the panel has a reasonably sophisticated deinterlacing algorithm. I think that at 60Hz if the panel wants to detect and deinterlace 3/2 pulldown material then it would need to delay it by 3 fields, pushing the minimum figure up to 50ms.

    If the panel is using 'bob' deinterlacing, this simply takes one field and scales it up (e.g. 576i50 becomes 288p50 and 480i60 becomes 240p60) and hence there is no deinterlacing lag (just the scaling one, which can be considered to be near-instantaneous). An example of this was in an article that claims some panels treat 1920x1080x50/60i as 1920x540x50/60p by using bob deinterlacing. I don't know if any panels do that at SD resolutions though.
     
  24. jon2099

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    spokx, sound about right (on both points), though I'm no expert. I'm not sure how long it takes for the transfer from the display's internal frame buffer to the panel itself though.
     
  25. Spokkx

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    very intresting, now I see. thanks :)

    As a gamer this mean no more scart-consoles.. component/hdmi all the way from now on..
     
  26. Caimbeul

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    a 40ms delay would mean you are running 66 frames per second behind what is actually happening in a game (assuming a 60fps source) that is far too much for any game in my oppinion...precision is crucial.
     
  27. Nic Rhodes

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    66 frames, are you sure?

    time lag on deinterlacing is also dependent on what chip you use, from roughly 30ms to upto 280ms, most are in the 40-60 for decent deinterlacing.
     
  28. Nic Rhodes

    Nic Rhodes
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    oh componet / HDMI will just change where the lag occurs.
     
  29. andrewfee

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    With progressive sources, there is no lag. End of.

    It only happens with interlaced sources, and as I said above, the XRGB2+ eliminates it. Scaling is so quick on current LCDs, the delay is negligible.

    I don't know how some people think the lag is less noticeable for games??? If anything it's more noticeable, as you're interacting with what's going onscreen, rather than just watching/listening.
     
  30. Spokkx

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    games are way more sensitive to lag than movies etc.. thank god the new consoles are progressive and you don´t have to deinterlace..

    as andrewfee said, you are INTERACTING with what you se in real-time.. every millisecond is important

    Caimbeul: 66 frames after?

    say you play a game in 60hz (60 frames per second)
    1 second = 1000 ms

    1000/60 = 17 ms per frame

    a 40ms lag for interlaced sources is more like 2-3 frames after
     

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