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50 hz vs 60hz -whats it all about

Discussion in 'Televisions' started by SwissTony, Sep 28, 2005.

  1. SwissTony

    SwissTony
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    I wonder if anyone can explain the importance of 50hz vs 60hz scanning at HD resolution?
    Which is the US Standard for 720p and 1080i?
    What will Sky and other European satellite broadcasters adopt?

    Are there some HD plasma models that manage 50 & 60Hz?

    I ask because I am looking to buy a HD ready plasma or LCD, but as I may get moved to the US next year I want to ensure that it is compatible with the US Satellite HD as well.

    Thanks
     
  2. Welwynnick

    Welwynnick
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    Basically, the US & Japan use NTSC 60 Hz video, and the rest of the World use PAL or SECAM at 50 Hz, because those are the mains frequencies. Most plasmas in the UK will run on both, but US plasmas are just NTSC 60 Hz. Sweepeing generalisations all, but that's the gist of it.

    The real issue with HD is that you really need an HDMI (or DVI) input, and with many supposedly HD-Ready displays, this doesn't accept 50 Hz at the display's native resolution, or wil convert it to 60 Hz for display. This means the display will expect either the wrong frequency or the wrong resolution - both bad for picture quality. It's an insane problem that most people don't know about, and which Pioneer and Panasonic are only just starting to get around. Remember if you want to take it to the US, you may be able to receive SD broadcasts, but you will need an external ATSC tuner, and maybe a mains transformer. (and a very good shipper).
     
  3. Batch

    Batch
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    Do Samsung's espacially the LE26R41B 26" suffer from this problem?
     
  4. SwissTony

    SwissTony
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    Thanks Welwynnick for the explanation. It is frustrating because so few manufacturers include this information in their specs. Do you know any true multi standard models?

    In realtion to your other points (voltage and TV Tuner) I have been doing my research.
    It is interesting to note that the two most popular producers -Pioneer and Panasonic do not make multi voltage models (neither do Sony or Philips). However Hitatchi and most cheaper brands do.

    I guess any external ASTC tuner with AV input (as opposed to RF) should work.
     
  5. Stephen Neal

    Stephen Neal
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    If you buy a display with the European "HD Ready" logo on it, it should support 50Hz and 60Hz inputs via both analogue component and HDMI digital (or DVI with HDCP) inputs - at both 720p and 1080i.

    If the power supply copes with the US 110V 60Hz input (or will be happy fed via a transformer feeding it 240V at 60Hz (rather than 50Hz) via a step-up transformer - then it will work on external HD inputs in the US. You would need to use an external ATSC, Satellite or Digital cable receiver bought in the US as a programme source though - as any internal PAL I or Freeview tuner wouldn't work in the US.
     
  6. Stephen Neal

    Stephen Neal
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    An ATSC receiver will have an RF input (which you connect to the aerial to receive the digital TV broadcasts - just like Freeview) and an HDMI or analogue HD component output which will go to your display. It will probably also have a composite or S-video standard def output to allow you to connect it to a DVD recorder or VCR for standard def recordings to be made.
     
  7. jensjens

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    Hi there,

    i was just having more or less the same question in the american avsforum on that.
    I moved back from Canada 2 months ago and I own a panasonic hd6uy industrial panel.
    I want to connect it to "premiere" (german hd provider from 11/01 on) through DVI. Problem is that the Panny only accepts 720p and 1080i in 60HZ through DVI. Premiere is transmitting in 50HZ through hdmi. All other analog outputs will be downscaled. So I am pretty much f'ed.
    Question:

    1) does anybody know if the DVI blade from Panasonic can be "convinced" to accept 50HZ.
    2) what happens if I connect the 50 HZ input to the 60HZ output. No picture at all?
    3) I have as well a denon 3910 MR. With this i can watch - and did watch - a lot of PAL DVDs - without any problems in 720p. How can that be. No jitter whatsoever

    Can anybody help and explain?

    @SwissTony: I called Panasonic regarding the power supply. They said that all their panels have an unpublished universal power supply from 90V to 260Volts. So no transformer need. But I have to admit I did not dare to try it out yet - it is connected to a transformer :)
    I attach the relevant mail from panasonic:

    Hello Jens,
    The plasma will operate OK, as it has an auto power supply built in,
    you may however need an adapter for the AC plug itself.

    Regard.
    Chris Robinson
    Broadcast Technical Support & Service
    > Panasonic
    > ideas for life
     
  8. Kalos Geros

    Kalos Geros
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    This is a real shame - I thought plasmas ran at 100 or 120 Hz at least to eliminate refresh flicker...we all know that 75 Hz is barely enough to use a computer comfortably...with every new technology there are some loose ends...when they finally will have put all the imaginable gizmos in HD plasmas, to prevent price drop about 25 years from now they will come up with a 100 hz plasma and market it as a next big thing, just like they did with a 100 Hz CRT...shameful...
     
  9. Logan09

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    Plasma, LCD & DLP screens display images in a different way to CRT screens, in that they display all the fields at the same time (progressive). Therefore, even at 50/60Hz there will be no flicker. So Don't worry.
     
  10. StooMonster

    StooMonster
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    1) nope, limitation of Silicon Image DVI Receiver chipset used on blade.
    2) no picture.
    3) PAL DVDs at 576p or 576i @ 50Hz are acceptable signal to DVI panny blade -- it's 720p@50Hz and 1080i@50Hz that do not work. They do work over analogue inputs though.

    StooMonster
     
  11. StooMonster

    StooMonster
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    Yes, CRT draws each field by sweeping one scanline at a time and relies on persistence of phosphor and human vision; whereas plasma, LCD, DLP update all pixels in an array at the same time.

    StooMonster
     
  12. Kalos Geros

    Kalos Geros
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    OK, so phosphor is a main culprit as it fades quickly so the initiation by the beam has to be performed at least 75 times or so per second for the human eye not to notice the fading of phosphor (percieved as full-screen flicker), wheras plasma and LCD elements can stay lit up much longer (I'm not that technical) and lower refresh can be used (although I assume that 25 Hz is too low, the eye is faster than that)...

    That explains it, then...thx, guys...
     
  13. Stephen Neal

    Stephen Neal
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    I think people are slightly misunderstanding how plasma panels work.

    As I understand it, having read up a bit, plasmas work not at 50Hz or 60Hz for their panel refresh, but at frequencies nearer 300Hz. They do this because they have to use pulse-width modulation techniques to (partially) deliver their greyscale, meaning that each TV field or frame is split into multiple sub-fields to generate the greyscale.

    Whilst it is true that the bulk of Plasmas are inherently progressive, the ALiS type (Alternate Lighting of Surfaces) DO use interlace scanning, and were developed specifically for 1080i interlaced sources for the Japanese market. (1024i ALiS displays are a good match for the original 1030i Japanese HD standard, now tweaked to 1080i.)
     
  14. Stephen Neal

    Stephen Neal
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    This isn't accurate in my experience.

    Large area flicker isn't related to interlace - and I certainly see large area flicker on plasma displays, though not on LCDs (presumably because the response time of LCDs is so high that they don't decay fast enough between frames?)

    Also - ALiS plasmas are not progressive AIUI they exploit interlace techniques to display a 1024i image.
     
  15. Welwynnick

    Welwynnick
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    Everyone thinks that plasmas illuminate all the pixels all the time.

    Well I distinctly recall reading a very authoritative source saying that they DO scan the frame progressively, a line at a time, just not a pixel at a time like CRTs.

    BTW, phosphor is not the culprit, because the persistence is tuned to match the scanning rate - the limitation is in the broadcasting, storing and electronics.

    BBTW, I believe the new 6 series Panasonic plasmas can display 100Hz under some circumstances - quite a step forwards.

    Nick
     
  16. Nick_UK

    Nick_UK
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    No, that's incorrect. In fact, to refresh a pixel on a plasma, you have to send a signal to extinguish the pixel before it is refreshed and re-lit. People have taken high-speed photo's of plasma TV's and have seen no sign of scanning.
     
  17. DanDT

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    Sooo.... Which HDTVs accept both 50 & 60Hz? And which ones only accept one of them?
     
  18. Stephen Neal

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    However plasmas don't deliver a grey scale in the same way that CRTs do - the pixel is either on or off AIUI - with no brightness control. To generate varying brightness levels plasmas use sub-fields of different durations, and switch the pixes on and off during these, as well as some dithering, to deliver a reasonable perceived bit depth.

    It is certainly possible to see the effects of these sub-fields if you point a broadcast TV camera at a plasma and then vary the content of the plasma. With certain contents you get horrible flickering on some models, as you get a beat frequency between the camera fields and the plasmas sub-fields.
     
  19. Stephen Neal

    Stephen Neal
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    All displays with the "HD Ready" logo will accept 50 and 60Hz signals in 720p and 1080i. It is part of the HD Ready spec.
     
  20. DanDT

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    Ok so it's safe...?

    You know, these days i'm still kinda cautious with these "HD-Ready requirements".
     
  21. Dutch

    Dutch
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    Jens,

    You would need to connect the Premiere box HDMI 50Hz output to a video processor such as a Lumagen VisionDVI which would do a frame rate conversion to 60Hz which the DVI blade will accept. This could result in judder which you may be susceptible to. Sorry, but I can't explain how your 3910 seemed to produce a 720p50 signal that the blade accepted. Strange...

    Steve
     
  22. StooMonster

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    Plasmas use the tried and tested frame-buffer technology.

    This technique is as old as the hills and where one rasterises a pixel-matrix in a buffer-frame and then copies the entire buffer over the display-frame; but only when rendering is complete, or interupt timer tells it to do so.

    This is usually achieved in a simple "copy memory block" command in processor, which is an even older technique. Copying line-by-line would be inefficient and resource intensive for no purpose.

    This process is what causes frame-buffer sync problems with some screens (plasma and LCD), where the screen has an interupt that operates this process at a fixed interval (e.g. commonly 60Hz, or 72Hz on older Pioneer plasmas). This causes judder when a signal is one frequency of update (e.g. 50Hz) but frame-buffer is fixed (e.g. at 60Hz), which is annoying as it should be fairly trivial to match frame-buffer update to signal.

    StooMonster
     
  23. Stephen Neal

    Stephen Neal
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    Yes - early plasmas had a fixed frame-store output at 60Hz, as they were designed to work with 60Hz inputs. When you fed them 50Hz sources they didn't alter to a 50Hz output scan, so you got judder.

    However the fixed output rate was probably chosen because plasmas run using very odd display systems - as I mentioned above - using sub-fields to generate their grey scale. This means they actually convert the output of the frame buffer into multiple display fields - so each progressive (interlaced in the case of ALiS panels AIUI) frame derived per field of a 60Hz signal may actually be split into 6-10 sub-fields, so the original 60Hz refresh rate may actually create a 360-600Hz sub-field system, with pixels only being illuminated in some fields, not others, to create a grey scale - effectively using pulse-width modulation. I think the sub-fields may vary in duration rather than being equal - to give a more logarithmic grey scale rendering?
     
  24. StooMonster

    StooMonster
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    Yes, absolutely, as next step frame buffer's pixels (in RAM) will be rendered to screen's physical plasma cells by sub-field processors; exactly as you describe.

    Point of interest, in my plasma (Panny 50" series 5) it's ADCs and internal circuity thoughout and even the scaler are all 8-bit, but the dual sub-field processors are 10-bit. Wonder why?

    However, my point was that plasma's pixels are not rendered to screen as welwynnick's assertation "...scan the frame progressively, a line at a time, just not a pixel at a time like CRTs."

    StooMonster
     
  25. Stephen Neal

    Stephen Neal
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    I'm not clear on how the sub-field pixels are illuminated. There is obviously a scanning process, as the system is still matrix based. Is there something like a small charge deposited by a scanning process which then causes a larger "strike" voltage to cause some pixels to illuminate and others not? Or is the strike voltage part of the scanning process ? From memory the strike voltage is only applied very briefly?
     
  26. StooMonster

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    When in doubt, search the patents...

    Checked out the EU and US patent databases and there are many patents linked to binary illumination devices (such as plasmas) and subfield processing: converting a grey-scale value into a series of on/off pulses to give the impression of graduation.

    This patent tracking site has a good example of a patent that discusses how subfields work: http://www.freshpatents.com/Plasma-display-and-its-driving-method-dt20041209ptan20040246207.php

    Tres interesting (in a very nerdy way :rolleyes: ).

    StooMonster

    PS: Even found the Alis patent on the US site.
     
  27. Welwynnick

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    Before anyone else thinks about reading that; take it from me - it's enormous, almost indigestible, not very relevant and life just isn't long enough. It didn't explain what I wanted to know - how the pixels are scanned - just the time domain characteristics for an individual pixel, with emphasis on luminous intensity non-linearity at low levels.

    Anyway, pixels are not illuminated continuously because they are either on or off, and the on/off time is modulated to give the greyscale. It's not pulse width modulated in the sense of a single pulse with a variable length that contributes to an aggregated signal. There are typically eight sub-fields in time per frame, the biggest being half, the next a quarter, and so on. These sub-fields are either on or off according to the binary number representing the luminous intensity for that pixel.

    Nothing new there. What's new to me is that the lines are not scanned. I spent 18 months thinking that they were. My problem is that each pixel AIUI is controlled by a horizontal pair of scan and sustain electrodes that connect all of the, say 1366 pixels in a row, and by a vertical address electrode that connects each of 768 pixels in each column. In other words, matrix addressing. So surely you can only address one row (or Column) at a time? I dunno, maybe there are nine million connections coming off the back of a PDP with their own individual drivers. Is that how it's done?

    It doesn't make any difference, because it works, and works fairly well, but I can't help being curious. I guess SED would work in the same way - just without all those sub-fields.

    Nick :confused:
     
  28. dUnKle

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    All these numbers and the like confuse me

    For a HCPC used for half region 1 and half region 2 DVD playback what should I use
     
  29. Stephen Neal

    Stephen Neal
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    How about two different screen modes - one for 50Hz and one for 60Hz? Powerstrip should let you switch quite quickly on the fly ISTR. (Or maybe 75Hz and 72Hz if you are mainly watching 2:2/3:2 de-interlaced film material and not video)
     
  30. Stephen Neal

    Stephen Neal
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    Having seen a lot of PDPs fail it is clear that some of them are based on half-panels, with the top and bottom half operating somehow separately. Not sure if there are two sets of panel drives, treating the top and bottom as separate displays effectively? It is common on the larger Fuji panels to see one half or the other die, or begin to not quite "strike" uniformly - so you get an intermittent image in one half or the other. When I say intermittent I don't mean the image flashes, more that varying horizontal portions of it stay black, with other horizontal portions in that half displaying image material.

    I would be interested to know exactly how the pixels are addressed and "fired", and also how the sub-fields operate (whether they are equal duration/brightness, or non-linearly weighted).
     

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