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Old 10th November 2006, 07:45 PM   #1
percy is offline percy  United States
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Default Q about spdif format for multichannel audio

How exactly does multichannel audio get transmitted in spdif format ? I am asking about the actual data structure/format of the stream.
I hear about IEC61937 (compressed) and IEC60958 (pcm) but have to yet to get a clear picture how the "high resolution" dolby and dts audio makes it over to the receiver.
Any tech/app notes anywhere that might help explain ?
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Old 10th November 2006, 08:50 PM   #2
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Default Re: Q about spdif format for multichannel audio

Quote:
Originally posted by percy

Any tech/app notes anywhere that might help explain ?
You have to pay for IEC and SMPTE documents but there is a version of the ATSC A52 (AC3) document with a pretty detailed appendix on AC3 over SPDIF. As it is free you may find a copy on the web.
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Old 10th November 2006, 09:48 PM   #3
percy is offline percy  United States
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is this the one http://www.atsc.org/standards/a52.html ?

I am wondering if they removed the AC-3 over spdif details in "Rev.B" ?
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Old 10th November 2006, 10:39 PM   #4
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It was removed in the 20/08/01 revision.
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Old 11th November 2006, 12:12 AM   #5
percy is offline percy  United States
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Oh well. I will keep searching, but in the meantime could anyone describe in simple english, how does multiple channels of high resolution data "fit" into those subframes ? Obviously there is some "extra" processing(compression ?) going on.

Besides that, the other information I am seeking is -
If there is some sort of a compression/decompression involved, then is it lossless ? or does the high bit depth and rate suffer ?

And in the light of that question, does it make any difference to let the receiver decode the signal i.e. send it to the receiver over spdif v/s let the player decode and use the analog signals from the player itself ?
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Old 11th November 2006, 12:41 AM   #6
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Quote:
Originally posted by percy
Oh well. I will keep searching, but in the meantime could anyone describe in simple english, how does multiple channels of high resolution data "fit" into those subframes ? Obviously there is some "extra" processing(compression ?) going on.

Besides that, the other information I am seeking is -
If there is some sort of a compression/decompression involved, then is it lossless ? or does the high bit depth and rate suffer ?

And in the light of that question, does it make any difference to let the receiver decode the signal i.e. send it to the receiver over spdif v/s let the player decode and use the analog signals from the player itself ?

No one fits multiple channels of high resolution data into SPDIF. IEC61937 and SMPTE337 et al. cover the transporting of compressed audio over IEC60958 (SPDIF). It is already in form of MP3,AC3, DTS etc. All the spec does is specify how to convey said data from point to point.
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