AC-3 encoding module idea

Discussion in '3-D Audio' started by dj_stick, Jan 4, 2004.

  1. dj_stick

    dj_stick Apple Fanboy?

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    IF we could find a simple IC that converts 3 stereo S/PDIF signals to AC-3, then it would be possible to built an output card like the optical output cards creative sells, just hook it to spdif_io or aud_ext.
    This only works if we can find a simple IC for the job that doesn't need any software control… then it would be harder
     
  2. daPyr0x

    daPyr0x New Member

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    dj_stick
    it's actually easier than that.

    AC3 = Dolby Digital S/PDIF
    yes, it is only physically 2 wires - (a normal 'stereo' connection is actually 3) but that's data and ground

    using the AUD_EXT headers on your audigy (LIVE_EXT for Live users; I'm not sure if the Audigy 2 has the same things or not) you have direct access to not only the data and ground connections, but also +5v for power.

    I actually used this knowledge to hard-wire my XBox's Optical output to my Audigy's S/PDIF input. This is the erason I'm not using the kX drivers - because unlike the Creative drivers, they couldn't decode the dolby digital....though it seems as if they can now, so I might try that out.

    Doing coax connections are a bit harder, I found it really difficult to get any useful information on such a thing; but doing it with optical in and out is quite simple

    here is a babelfish translation of the german site that I used....

    Now, I didn't use their inverters or capacitors; and truthfully I'm not sure why what all they did is even neccesary...what I did was wire directly to the data and ground wires of the optical connector on the XBox's output, and just run the wire onto the SPDIF IN and GND connections. I did, however, have to do the VCC -> 4k7 resistor -> GPIO wire that they did which tells the card that there's anything connected.



    The tough part of the Audigy Drive would be getting analog inputs/outputs, because the drive does analog -> digital conversions.
     
  3. dj_stick

    dj_stick Apple Fanboy?

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    Dolby Digital differes from S/PDIF, s/pdif is only 2 channel, ac-3 is compressed data sent as 2 channel and then decoded
     
  4. daPyr0x

    daPyr0x New Member

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    Dolby Digital is compressed into the AC-3 format and sent over the S/PDIF interface....
    in my mind, this works as AC-3 = Dolby Digital over S/PDIF.

    regardless, what I did works.
     
  5. tommy_99a

    tommy_99a New Member

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    I've found a site that maybe match your (and my) desire.

    it's a realtime software ac3 encoder for linux (and the best: its under GPL)

    http://essej.net/ac3jack/

    maybe ther is anybody who can translate the sourcecode tho emu10k2 assambler
     
    Last edited: Feb 15, 2004

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