Digital cable: better picture with s-video or coax?

Discussion in 'Beginners, General Questions' started by Fred G, Oct 26, 2003.

  1. Fred G

    Fred G Agent

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    I recently got digital cable and upon receiving the box I noticed it had a digital audio out, as well as an S-Video out.

    Now the analogue digital audio out has obvious benefits, as the cable box outputs a signal that is split into 5 channels.


    However I don't see how the S-Video can give you any benefit when the original source (the cable from the cable company) is a coax cable. Wouldn't a coax-in (into the cable box from the wall) and a coax-out (from the cable box to the TV) be the "cleanest" connection? I would think so, since as with anything, you loose quality the more you "process" the signal.

    It's kind of like saving a .jpg on your computer. Every time you save that picture, it gets compressed and the picture degrades a bit.

    However after calling the cable company, one of the tech representatives said that the S-Video will give me a better picture because of the way the signal is processed. But this just doesn't make any sense to me. "You can’t get a better picture than the original source," I thought. Wouldn't that be violating some law of of physics?

    After doing some unscientific testing, I've found that my untrained eye can't tell the difference between the coax signal and the s-video signal. However in the back of my mind I'd always like to think I'm not "loosing" picture quality by using one over the other.

    So does anyone know the truth behind these digital cable boxes? Can S-Video give you a better picture even if the original source itself is coax?
     
  2. John Garcia

    John Garcia Executive Producer

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    It doesn't matter how the signal gets to the box, since what you see on the TV is being decoded at the box, so it is possible to get a better picture with S-video. Without changing settings on the TV, you will not see a difference between the two. Using a calibration disc such as Digital Video Essentials or Avia will likely help.
     
  3. ChrisLazarko

    ChrisLazarko Supporting Actor

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    Well I don't own a digital cable box but... with my DVD play I used to use the composite out (yellow line) and when I upgraded to Component (Red,Green,Blue) I noticed a big difference on my TV. The colors didn't bleed anymore, the signals were a bit sharper as well.

    I did have S-Video for a while and I noticed a little imrpovement as colors wouldn't bleed with black like on a normal coax cable.. so I would say go for it, you can find S-Video cables for a good price usually.
     
  4. Lew Crippen

    Lew Crippen Executive Producer

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  5. Fred G

    Fred G Agent

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    Thanks for the responses.

    John, I don't know why I didn't think of that before! It's a digital signal so it shouldn't even matter how the original source was delivered. [​IMG] Somehow this slipped my mind.



    I guess I'm surprised at how good the coax signal is. I can definitely tell the difference between coax and composite. Composite is horrible in regards to lack of sharpness and increased color bleeding. However coax seems pretty much on par with S-video, which I found somewhat strange as I always thought coax was the lowest quality of analogue signals (a frame of mind stemming from using "rf adapters" for various types of video sources). I will continue to use S-Video since it provides convenient audio/video switching via my receiver.
     
  6. Allan Jayne

    Allan Jayne Cinematographer

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    I cannot explain why the channel 3/4 RF coax feed and the S-video feed from the cable box are both better than the composite video feed. You might try a different composite cable into the TV.

    For digital cable, the coax feed from the wall is digital and not the same as the coax feed from the box to the TV which is analog.

    For the coax feed to the TV, the video comes into the cable box, the proper channel is selected, if digital it is converted from component video into S-video into composite video and is remodulated onto channel 3 or 4 then sent to the TV where it goes through the TV tuner, comb filter and color decoder. If the channel is analog the box remodulates it onto channel 3 or 4 and then sends it to the TV where it goes through the TV tuner first.

    For the composite feed to the TV, the video comes into the cable box, the proper channel is selected, if digital it converted from component video into S-video into composite and sent to the TV where it goes through the TV comb filter and color decoder. If the channel is analog it goes directly to the TV where it goes through the comb filter first.

    For the S-video feed to the TV, the video comes into the cable box, the proper channel is selected, if digital it is converted from component video into S-video and sent to the TV where it skips the comb filter and goes to the color decoder. If analog the cable box comb filters it (usually mediocre-ly) and sends the resulting S-video to the TV and the color decoder gets it next.

    I can't find any part of the video signal path used by composite and not by the other two, where the degradation might occur.

    Because of the signal paths as described, sometimes analog channels will be better via composite as opposed to component or S-video.

    Video hints:
    http://members.aol.com/ajaynejr/video.htm
     

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