Source of intererence in a/v output, camera's signal, cable itself, or tv?

Discussion in 'Professional Video Production' started by Richard Crowley, Dec 14, 2003.

  1. How many different monitors/TVs have you tried this on?
    How do you know if it is the camcorder, cable, or monitor?
    My first suspect would be the monitor/TV.

    Some of the symptoms sound like poorly-blanked retrace
    lines. (A symptom of an aging TV)

    How much experience do you have with video? Hard to
    distinguish some of your complaints between native artifacts
    of consumer video vs. actual equipment malfunction.
     
    Richard Crowley, Dec 14, 2003
    #1
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  2. Richard Crowley

    steven Guest

    (Cross-posted this to rec.video also seems like not everyone follows
    both groups.)

    I want to output the mini-dv video I taped to my tv.
    The tv does not have s-video jack. Only the audio/video (a/v) jack,
    that has the yellow video wire and the red and white audio wire.

    If I hook the camcorder up to the tv and play the tape, I see faint
    horizontal lines that maybe move a little bit (sometime upwards). The
    lines are brighter than the background, and easiest to spot when there
    is a dark background (black colors). They are very hard to spot in a
    brighter picture. They are not always constant. Sometimes these
    faint lines are spaced 1 cm apart. Sometimes they seem almost
    non-existent. If I rewind a section oft the tape and replay it, the
    interference may be different. I do not even have to play the tape to
    see the intererence. Rather I can set the camcoreder to were you set
    up to record video, and see the intererece. Sometimes the lines are
    not perfectly horizontal They can be a slightly diagonal pattern that
    almost seem more like a broken faint line that is defined by slight
    dotted intererence. This effect is most apparent if I hook the a/v
    jack to the vcr's input. The vcr is attached to the tv. I can really
    adjust the nature of that interence by moving the coax cable that
    hooks the vcr to the tv. So clearly most of that interference is in
    the vcr to tv connection. However, the more horizontal lines that I
    described at the begining of this paragraph are when the mini-dv
    camcroder is hooked directly to the tv's a/v input. Unpluging the
    coax cable that also runs out the back of the tv, near the a/v inputs,
    seems to have no effect on the intererence that may or may not occur
    in the mini-dv camcorder to tv a/v connection. So there does not seem
    to be any crossover intererence there.

    Sometimes, there appears to be no distinct intererence like that. It
    is easiest to tell the interence , by putting the lens cap on the
    mini-dv camcorder while the camcorder is in the standby to record mode
    (effectively the tv is a real time monitor, mirroring what I see in
    the camcorder's lcd).

    So my question is, is this a fault of the a/v output of my mini-dv
    camcorder?

    Would a better (newer tv --this tv is 7 years old) television, take
    care of this problem (is it that there is not enough shielding in the
    tv?

    Would s-video input eliminate this?

    When I have the lens cap on the mini-dv camcorder, in standby, and I
    see the image on the tv through the a/v connection, even when I do not
    see little faint intererence lines, the black I do see is not
    perfectly jet clear black, rather it is a slightly dancing (for lack
    of a better descriptive word) fuzzy black. This underlying
    grainularity to the black shows through regarless of whether there is
    gain up in the camcorder (that grain from gainup can be seen as a
    slightly other type of granular shimer superimposed on this base black
    grainlurity I am describing).
    Why do I not see perfect black and no granularity with the lens cap on
    (and no gainup)? Would I see a perfect black if the signal traveled
    over s-video? Over a firewire transfer to computer to examine the
    video? Where is this interference coming from? Is that base black
    granularity I describe, interference?

    Do you suspect there is anything wrong with my new camcorder?

    Thank you.
     
    steven, Dec 14, 2003
    #2
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  3. Richard Crowley

    steven Guest

    Would a better a/v cable help. It does not seem to change depending
    on the positioning of the cable next to the tv or whether I bend it or
    not.
     
    steven, Dec 14, 2003
    #3
  4. Richard Crowley

    Larry Jandro Guest

    I suspect that you have an aging TV. Try playback on a newer
    monitor.

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    Larry Jandro, Dec 14, 2003
    #4
  5. Richard Crowley

    steven Guest

    Only one tv so far. I will have to take it to the store and test on
    one of their tvs.
    I do not know what it is. That is what I am asking the group here. I
    would think the a/v cable that came with the camcorder was good.
    Wouldn't you?
    Yeh the tv is about 7 years old.
    I have no experience with mini-dv. I have some experience with hi-8.
    I am not experienced, just observant.
    When the lens cap is on the video camera, with no gainup. Should that
    look like a perfectly black image with no faint black snow when viewed
    through the tv via tha a/v cable? Does that faint black snow come
    from the tv's searching for a a/v signal?

    Thanks.
     
    steven, Dec 14, 2003
    #5
  6. "steven" wrote ...
    It is low-level video "noise". Could be half a dozen reasons
    you can see it. I'd sure suspend any judgement until you find a
    good monitor/TV to view it with. You've got one equation and
    three or four unknowns here.
     
    Richard Crowley, Dec 14, 2003
    #6
  7. No. Seems highly unlikely. It would be my last choice of suspects.
     
    Richard Crowley, Dec 15, 2003
    #7
  8. Richard Crowley

    Hughy Guest

    A couple of possibilities (however unlikely...)

    If movement of the coax alters your displayed image, it's possible you
    may be picking up external RFI.

    Another (almost negligible) possibility could be radiation of the video
    baseband signal into the TV - with the direct (cable) signal being, with
    movement, variably out of phase with the radiated signal - via EM
    propagation. As you move the cable, the phasing of the two signals
    change, causing your image interference pattern to change. This usually
    presents more as a ghost image than a interference pattern. And the
    signal level on your output cable is only of the order of 1V peak - not a
    level usually associated with unwanted radiation (when correctly
    terminated) - at least on something as relatively insensitive as a TV
    receiver.

    Your existing cable may be poor quality, some use el cheapo very sparsely
    interleaved outer braid. The best contain a thin continuous aluminium
    shield as well as the braid, normally overkill for domestic purposes.

    You may well find that use of an S-Video cable to a different monitor
    solves the problem.

    Regards,
    Hughy.
     
    Hughy, Dec 15, 2003
    #8
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