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24hz and 25hz

Discussion in 'Desktop & Laptop Computers Forum' started by bfrench, Mar 20, 2005.

  1. bfrench

    bfrench
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    Hi,
    Most people here seem to use 50 or 75hz for PAL
    material and 48, 60 or 72hz for NTSC. Is there any
    reason why I should not use 25hz for PAL and 24hz
    for NTSC? Quite often Reclock advises a multiple of
    these and as flicker isn't a problem (DLP pj) I should
    be able to use them shouldn't I?
    Are there any advantages/disadvantages that I should
    be aware of?

    Barry
     
  2. bfrench

    bfrench
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    I've just realised that I can't get 24hz but I
    can get 25hz (SIM2 domino 20H)

    Why would 50 or 75 be any better?


    Barry
     
  3. KraGorn

    KraGorn
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    The main reason people use multiples of 25 is that some types of display, especially digital panels, don't support such low refresh rates a 24 and 25.

    If your display handles them then 24, 25 and 30 are optimal as multiples of them cause frames to be doubled and the guy who calibrated my system, when I asked him about this, told me that some people can acutally see the tripling of frames you get if you use 75 for PAL or 72 for NTSC..

    25 is always right for PAL, 30 is for NTSC derived from video and 24 for NTSC derived from film .. I have to admit not knowing why but experience shows it's the case. :)
     
  4. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    25 frames per second and 24 frames per second are only of use for film sourced material. If you watch something recorded on video camera's interlaced at 50Hz or 60Hz it's likely to look a mess at those refresh rates.

    Gordon
     
  5. KraGorn

    KraGorn
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    Ooops, I meant 50 is always right for PAL even though it doubles the frame-rate for film material.

    Tell me Gordon, something I've never figured .. AIUI all movies are shot at 24fps, when converted to PAL how is the frame-rate converted? Or is the famous 4% PAL speed-up?
     
  6. Rob100

    Rob100
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    Yes movies are shot at 24fps and then sped up by 4% when converting to PAL or slowed to 23.976 and have 3:2 pulldown applied to take up to 29.97 for NTSC (59.94Hz).

    Rob.
     

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