What does this mean "Balanced Digital Output"

Discussion in 'Archived Threads 2001-2004' started by David Proud, Jan 21, 2002.

  1. David Proud

    David Proud Stunt Coordinator

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    I have been looking for DVD players with outstanding video and audio output. I have run across a term in one of the higher end DVD players that I have not seen listed on the mid to lower end line of dvd players. It is called balanced digital output. What is balanced digital output? Do all dvd players have balanced digital outputs or is this something only found in expensive dvd units.

    For instance would the Panasonic RV-91 have balanced digital output?

    Do all dvd players sound the same using the digital out connection in DD or DTS? If not what players provide the best transport to a good receiver or sound processor?

    Thanks,

    David
     
  2. John Kotches

    John Kotches Cinematographer

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    It is almost certainly referring to the AES/EBU digital output interface, which utilizes the XLR connector between player and decoder.

    There are few components on the market (receivers or processors) that can handle an AES/EBU input, and those that can (as you've noticed) are on the expensive side.

    I've had a fair number of DVD-V players in my system and have only noticed marginal differences at best on DD and DTS soundtracks.

    Regards,
     
  3. David Proud

    David Proud Stunt Coordinator

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    So the idea here is to buy the dvd player with the best possible video performance and forget about the digital audio output which is much less the same between a 200$ player and a 2500$ camalot.

    What if I where to purchase an AES/EBU sound processor. would I benifit from adding a DVD player with AES/EBU output for DD and DTS over using a DVD player with the standard SPDIF output.
     
  4. John Kotches

    John Kotches Cinematographer

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    David,

    There's also CD and 24bit/96K from DVDs as a capability, there I've heard more substantial differences.

    I have not yet had the opportunity to test AES/EBU in my system.

    It's just that DD/DTS sound are more a function of the receiver/processor than it is the player, because of the nature of the signals being passed.

    Regards,
     
  5. David Proud

    David Proud Stunt Coordinator

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    Hi Thanks for your help!

    I was looking into the Camalot Round table DVD player. It features awesome video and It says it features dejitter 5.1 bitstreams and upconverts DVD to 24/96KHZ. If I bought this player would I notice an improvement in fedelity over buying a DVD players under 1000$?
     
  6. John Kotches

    John Kotches Cinematographer

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    David,

    When I tested the Camelot, I found it did for CDs. It's a quite expensive player though, and you'll have to decide for yourself if the improvements merit the expense.

    For DD/DTS I noticed no substantive improvements.

    Regards,
     
  7. RichardH

    RichardH Supporting Actor

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    So, on a "balanced" digital connection utilizing AES/EBU, is there signal on both pins 2 and 3? If so, what are they? It's not balanced in the sense that a regular mic cable XLR is balanced, right?
     
  8. John Kotches

    John Kotches Cinematographer

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    Richard,
    Why can't AES/EBU be balanced in the same sense that an analog cable is balanced?
    The point of the balanced connection is to lower raise (or lower depending on perspective) the SNR, by allowing for Common Mode rejection.
    CMR plays in the digital realm too, and you only have 1 shot to get the "bit" right [​IMG]
    AES/EBU was originally intended for professional environments where longer cable runs (and hence noise) becomes a factor.
    Regards,
     
  9. RichardH

    RichardH Supporting Actor

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    So, how does one flip the "phase" of a digital signal? Is it 1 when it's supposed to be 0 and vice versa? Then it's flipped at the other end and combined? What if the two are different, what do you go with??
    What signal is pin 2 carrying?
    What signal is pin 3 carrying?
    Are they different? How?
    Not jumping on your case, John, but I am curious...
    and I'll be grateful if you can explain it.
    EDIT:
    I just read the pdf document of the AES/EBU spec and there is a part that talks about common mode rejection on a balanced signal. It says that common modes will be at least 30dB down. I guess in digital terms that means less likely to cause an error. But, it also looks like the likelihood of an error is extremely low, even on long runs.
    Also, there is another part that describes the use of an XLR cable to transmit the digital signal, and that the relative polarities of pin 2 and pin 3 are not relevant in digital.
    If pin 2 is carrying the opposite of pin 3 then how would it know what the 'correct' signal is supposed to be?
    The document wasn't detailed enough for me to figure that out. Or maybe I don't know enough about it yet to figure it out from the document.
    Many thanks, John, if you can clear it up for me! [​IMG]
     
  10. John Kotches

    John Kotches Cinematographer

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    Richard,
    I'm not a super high-level expert on this topic, so forgive me if I don't explain this very well, ok?
    The digital signal on a cable isn't "on/off", it's actually a combination of pulses.
    This is an image showing the "Biphase" modulation used to transmit the signal:
    [​IMG]
    You have a mandatory transition from high/low or low/high to signal the start of a bit. Another transition signals a 1, no additional transition equals a 0.
    Because this is a square wave, and you're dealing with voltage ranges, you can do addition/subtraction via inversion and the only thing lost is the noise.
    There is much more detailed information you can get started with from this page http://www.epanorama.net/links/audiodigital.html#spdif
    Regards,
     
  11. RichardH

    RichardH Supporting Actor

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    John, thank you!! [​IMG]
    I actually know about biphase modulation. I think there's the name "manchester" in there too. Don't know why I didn't think about it that way. Guess I had the blinders on [​IMG]
    So, it's unlikely that noise would cause an error to happen (1 instead of 0), but with balanced digital it's that much more unlikely; very neat!!
    Thanks for taking the time to explain that.
     
  12. John Kotches

    John Kotches Cinematographer

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    If you know biphase, then you probably know NRZI, right?

    CDs and DVDs use NRZI for encoding on the media.

    Regards,
     

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