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  1. #1
    Member KennyFeng's Avatar
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    Apr 2009
    Nanchang,Mainland China

    Will Audio Embedders and DeEmbedders introduce A/V relative timing problems?

    Say, when a lip-synced serial digital component video signal with embedded audio passes through a de-embedder, does the de-embedder need a gen-lock or it just locks to the clock recovered from its own SDI input? Do embedders and de-embedders cause lip-sync problems? If they don't, can they adjust such problems in their incoming signals? Thanks.

  2. #2
    From what I embedder (or MUX, or Mulitplexer), or a De-embedder (DEMUX, or Demultiplexer) should not need an external reference signal (genlock). It uses the SDI stream clock.

    I guess there are 2 question here....
    1) Does a MUX affect lipsync?
    2) Does a DEMUX affect lipsync?

    The simple answer to both is no.

    Question 1) A MUX will retain lipsync as long as the incomming video and audio are already "lipsync'd".
    Question 2) A DEMUX will retain lipsync as long as the resulting outgoing video and audio are fed to equipment that is genlocked together.

    Attached are 2 manuals to help (MUX op manual, and DEMUX op manual).
    Attached Files Attached Files

  3. #3
    Member KennyFeng's Avatar
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    Apr 2009
    Nanchang,Mainland China
    Thank you for your reply. I've read some manuals including what you recommended. And here are my opinions ----
    1. the MUX and DEMUX do introduce delays but either they're in insignificant amounts(serial scan lines) or introduce same amounts of delay to the video and audio(embedded SDI stream) data so their outputs are still lip-synced to the viewers;
    2. SDI frame synchronizers, as I read in some manuals, do introduce delays in amounts varying from several lines(for example, Evertz 7746FSE-HD, to 1 frame plus, but for SDI input with embedded audio, it will keep the original lip-sync status;
    Am I correct?

  4. #4
    Senior Member SC358's Avatar
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    May 2005
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    Hi KennyFeng -
    In both items 1 & 2 you are correct.

    Whether (de)muxing- audio is being processed, actively! So there has to be some delay in the process. It depends on the manufacturer circuitry if they include a way to compensate for any delays regardless a/v. As the signals go thru other processors, (i.e. frame synchronizer, distribution amps, routing switcher etc.) there's always a possibility of lip-sync problems. The question is which do you delay, audio or video? And then what happens, because you can't really advance anything.

    Beware of the path of least resistance....
    Relationships are based on compromises - behavior accepted is behavior repeated.

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