AUDIO : Optical, coaxial, HDMI - differences?

Discussion in 'Cables & Switches' started by Matt_C, Jan 25, 2008.

  1. Matt_C

    Matt_C
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    Okay, so we all know that optical, coaxial and HDMI cables can transfer bitstream digital audio, to a reciever geared to decode this bitstream.

    I was just curious tho - we all use optical and coaxial for our 5.1 channel audio, and HDMI makes a big thing about it's ability to carry "up to 8 channels of uncompressed digital audio" - how much, or rather how many channels, can an optical/coaxial cable carry? Can they do 6.1? Can they do 7.1? (obviously as long as the source material has it and the reciever can decode it), could these cables do the same job as HDMI in the audio stakes?

    Whats the limitations of optical and coaxial cables, and why?

    :)
     
  2. gblades

    gblades
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    Optical/co-ax can do 6.1 and 7.1 but it has limited bandwidth so can only transfer the compressed version of the audio. So if you want to output pcm then optical/co-ax can cope with 2 channels but not 5.1 or above. For this you need HDMI.
     
  3. MarkTaylor

    MarkTaylor
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    In short, optical/coax is limited to 125 Mbit/s, HDMI is now at 10.2Gbit/s

    You can't send the new HD audio formats across optical/coax as they can't handle it.

    It isn't that optical fibre couldn't do the job, but the equipment you'd need at both ends is very different to what is currently installed in our AV gear.

    Optical can handle 6.1 and 7.1 within the Dolby and DTX EX format but it can't handle the new HD uncompressed formats as they just need too much data to be shifted.
     
  4. Matt_C

    Matt_C
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    You say the equipment at both ends needed is different to what we have, if we had this different equipment, could optical and/or coax send uncompressed multichannel?
     
  5. MarkTaylor

    MarkTaylor
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    It simply isn't going to happen though.

    The capacity of optical fibre isn't ever a problem, the practicality of the electronics needed at both ends is still the limitation and the need to set and agree standards for doing it so that equipment will play nicely together.

    10Gig fibre links are increasingly used in the internet industry for peering interconnects so the technology is well proven and of course much faster speeds are used elsewhere in the telecomm's industry, but it is cheaper and easier and far more robust in a domestic situation to use the HDMI copper based solution.
     
  6. Matt_C

    Matt_C
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