Artifacts on CBS, but not on ABC

Discussion in 'Windows Media Center' started by Luis, Nov 23, 2004.

  1. Luis

    Luis Guest

    Same signal strenght in all digital channels, same SNR (verified with OTA
    receiver). Shows recorded from CBS have lots of video artifacts, especially
    when actors move quickly or when there a change in sequence. Almost no
    artifact in ABC signals for same type of content, ect.

    Any idea of what could be wrong?

    3Ghz Presscott / 1Gb RAM / ATI HTDV / NVIDIA decoder / ATI x800 feeding a
    42" Panny EDTV plasma display using component video. ATI X800 using custom
    res. mode (a modified 720p) to avoid overscan.
     
    Luis, Nov 23, 2004
    #1
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  2. Only thing that comes to mind is that ABC broadcasts in 720p, whereas CBS is
    1080i .
     
    Cari \(MS-MVP\), Nov 23, 2004
    #2
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  3. Luis

    Luis Guest

    Thanks for the quick answer. I believe both NBC and WB do 1080i as well, and
    I don't see artifacts there either - anybody else with an ATI HDTV card
    having issues with CBS? Anybody with an NVIDIA deco having issues with CBS?
     
    Luis, Nov 23, 2004
    #3
  4. Luis

    JW Guest

    Are you seeing ghosting on all images or only on moving images? If yes what
    you have are called motion artifacts and they are normally caused by
    broadcasting without enough bandwidth allocated to keep up with rapidly
    changing screens. This is due to the fact that the video is compressed
    using MPEG2 format which only transmits changes in screen frames whenever it
    can and too many changes require higher bandwidth.
     
    JW, Nov 23, 2004
    #4
  5. Luis

    Luis Guest

    They are motion-related, but I have to doubt that this is an encoding issue
    in a large market such as Atlanta. My guesses as of now:

    a. the ATI HDTV card is acting - but why only CBS if all of them have
    similar RF reception parameters?
    b. the NVIDIA deco is acting - but why only CBS, other 1080i shows are fine?
    c. the X800 is acting - down res from 1080i to 720p to fit Panny - but why
    only on CBS?
    d. I don't know what I don't know

    Any help is greatly appreciated.
     
    Luis, Nov 23, 2004
    #5
  6. Luis

    JW Guest

    It is not an encoding issue. The signal is already encoded before it is
    transmitted. It is not a decoding issue since other channels work.
    I very much believe that it is a transmission bandwidth issue since each
    station is allowed to decide how much bandwidth it will allocate to the
    transmission of each sub channel its uses. It appears that CBS Atlanta is
    allocating less than other Atlanta stations therefore not everything gets
    transmitted in high motion situations.
    I suggest you got to www.AVSforum .com - HDTV Forum - then the - Local
    HDTV info and reception sub-forum - Atlanta, GA OTA thread - and look for
    some answers there, or post your problem there.
     
    JW, Nov 23, 2004
    #6
  7. Luis

    RichT Guest

    In the Seattle area and I'm also seeing artifacts in fast
    motion sequences. I have the ATI HDTV and the NV DVD
    Decoder, however my graphics card is an ATI 9800 and
    being output using svideo to a regular old TV.

    I thought I was seeing it on all channels, but I'll
    double check to see if maybe it's only the ABC like you
    say.

    Cheers
    RichT
     
    RichT, Nov 24, 2004
    #7
  8. Luis

    Luis Guest

    Thanks, JW. It makes sense. I'll ask around in AVS forum. Very silly of CBS
    if they did this...

    The part that can be tricky is that other HDTV receivers (non-HTPC) may have
    a mechanism to compesate for the lack of received info (would this be similar
    to first DVD players dealing with scratches far worst than new ones?).

    Again, thanks.
     
    Luis, Nov 24, 2004
    #8
  9. Luis

    Luis Guest

    Thanks, RichT. In that case I may rule out the graphics card and the
    downconversion in the plasma display - either ATI HDTV or NV deco. The only
    way that I can think to figure it out now is to install the ATI HDTV card
    using their apps instead of MCE2005+NV deco and see if the artifacts are
    there for the same shows in CBS...

    Thanks, again.
     
    Luis, Nov 24, 2004
    #9
  10. Luis

    JW Guest

    If it is a bandwidth then it is your CBS Atlanta station, the stations all
    receive a full broadcast from Network headquarters.
    I have not seen any information on how to correct for this. Recently there
    was a similar problem on several HD channels from my local cable supplier
    and it took a lot of complaining to get them to allocate more bandwidth.
     
    JW, Nov 24, 2004
    #10
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