Can dot crawl be eliminated?

Discussion in 'Archived Threads 2001-2004' started by ScottR, Jul 18, 2002.

  1. ScottR

    ScottR Cinematographer

    Apr 1, 2000
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    Can dot crawl be eliminated with any special cables or hookups? I noticed that the opening mural of "Roots" has terrible dot crawl on the lettering of the title. This does not appear on the vhs version. Can an "S Cable" hookup help eliminate the problem, if this is indeed what it is.
  2. Bob McElfresh

    Bob McElfresh Producer

    May 22, 1999
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    Dot crawl can be dramatically reduced by using a SVideo or Component video cable rather than the single Composite video cable.

    But - you must start with a source that keeps the video separated. DVD's do this, and DSS systems do.

    You can buy the little $20 "Composite to SVideo" adaptor from Radio Shack, but the quality is very poor because it's a cheap little filter. (Dot crawl is caused by less-than perfect filters).

    Try this: go buy a SVideo cable that can reach from your DVD player to your TV. Hook the SVideo and a Composite Video from the DVD player straight to the TV. Start a movie with lots of bright colors or sharp/straight lines. Pause on a frame.

    Toggle your TV back and forth between the SVideo and Composite signal. You should see a dramatic drop in dot-crawl with the SVideo feed.

    Hope this helps.
  3. gregstaten

    gregstaten Supporting Actor

    Aug 1, 1997
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    Bob's answer is true "IF" the DVD was source from a component source. Though this is certainly the case for virtually every feature film release, some of the older television material was originally mastered on a composite tape. For example, much of television programming up to just a few years ago was finished (onlined) on composite tape. Depending upon the age of the product it may have been 2" Quad (mid-sixties to late eighties), 1" Type C (mid-seventies to mid-nineties), or D2 Digital Composite (late eighties to late nineties). (Note - the switchover from one format to another varied from location to location.)

    By the early nineties some television was finished on a component tape format, - but the majority until the late nineties was still finished on composite tape. For example, as recently as two years ago much of ABC's programming was mastered on D2.

    Based on the time ROOTS was produced, I believe it was finished on 1" Type C but it could have been Quad. Though some shows in the seventies "cut negative" it is possible that the negative was not properly stored and the best extant copy was the videotape master. BTW - few shows today cut negative. The negs and the cut lists are vaulted, but few are actually cut. (Note - I have no firsthand information on ROOTS, but know what was typically done back then.)

    Because these formats are composite, all of the problems with composite are part of the format - dot crawl, cross-color moire, and so on.

    When these shows are dubbed to component tape, the quality of the comb filter used to separate out the chroma subcarrier will determine whether or not the component artifacts are reduced. Of note, the further the composite source used for the dub is from the original master, the greater the amount of composite artifacts that have to be reduced - sometimes more than can be accomplished with all but the most expensive equipment.

    So, if the dot crawl (and other artifacts) was recorded into component tape, they are there and will always be visible if you view the program via the component or s-video outputs.

    Here's the irony. The comb filters in modern tvs are extremely sophisticated and you may actually get a cleaner image if you connect the COMPOSITE out from the DVD player to your tv. For example, I have one DVD where this is true: Elephant Parts. The composite artifacts are horrendous and are part of the bitstream. However, if I hook up my DVD player via composite, the image looks much much better.


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