what is a 3-line Digital Comb filter ?

Discussion in 'Archived Threads 2001-2004' started by ethan_l, Dec 3, 2002.

  1. ethan_l

    ethan_l Stunt Coordinator

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    I think I have this feature on my samsung RPDHTV
    but it can only be enabled in the service menu
    and when ever I do it
    my TV signal(antenna) looks like crap

    thanks
     
  2. Jan Strnad

    Jan Strnad Screenwriter

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    Reminds me of an old Henny Youngman joke (as if there were any new Henny Youngman jokes).
    A man goes to his doctor, raises his arm and says, "What should I do, Doc? It hurts when I do this."
    The doctor says, "Don't do that."
    A comb filter splits up the red, blue and green signals from a composite signal. Why this would screw up your OTA signal, I don't know.
    Since you're messing in the service menu with a feature you don't know what is, I recommend that you back away slowly from the set and leave it alone before you screw up something serious. For instance, it's possible to turn off all three CRTs from the service menu; getting them back on again when nothing displays on the screen would be a trick.
    In short, "don't do that."
    Jan
     
  3. Bill Slack

    Bill Slack Supporting Actor

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    I'd guess your disabling it in the service menu.

    And it does seperate RGB from the BW signal, but not from each other. The siginal is basically kludged on top of the BW signal and a comb filter tries to seperate it intelligently and with the least amount of noise.
     
  4. Jan Strnad

    Jan Strnad Screenwriter

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    Thanks for the correction, Bill!

    Jan
     
  5. Allan Jayne

    Allan Jayne Cinematographer

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    All TV broadcasts and composite sources must go through a filter generically known as a Y/C (luminance/chrominance) separator. A comb filter is a Y/C separator. If it can be disabled, a cheaper separator, usually a filter known as a notch filter, is substituted. There are a very few video sources, less than one percent and notably computer generated, that look better using the notch filter, thus the choice in the service menu.
    For normal viewing the comb filter should be engaged, and the TV should come from the factory with the comb filter engaged. Because service menu captions are often cryptic, it is easy to disable it when you think you are enabling it. The final preference is up to you. Some comb filters, particularly those with "two lines" instead of three, introduce lots of dot crawl and noise.
    Video coming in via the S-video and component video jacks does not go through, and does not need, the comb filter.
    To see whether the comb filter is engaged, play the AVIA 200 TVL pattern or the Video Essentials pattern with a big circle in the middle and four little circles at the corners. With the filter engaged, the upright wedges should be clear to at least 350 lines of resolution on the scale provided. With the filter disabled, the upright wedges will blur starting at 250 and there will likely be pink and blue splotches above that point.
    Video hints:
    http://members.aol.com/vidcomb.htm
     

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