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Help me understand BD Audio through Optical

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#1 of 4 Geoff H

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Posted August 23 2010 - 04:16 AM

OK, so I know that if I connect the BD player to the receiver via Optical (no HDMI) that the audio will be "downmixed" to DD and/or DTS -- how does this work?


That is, does Dolby True HD/DTS HD somehow "convert down" (through optical) to Dolby Digital/DTS or are there non HD audio on the disc as well and it's using the non HD tracks if there is not an HDMI connection???


Thanks in advance,




#2 of 4 moovtune


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Posted August 23 2010 - 04:38 AM

For DTS, the format works by having a "core" element that is playable on all DTS capable decoding devices. The High Resolution or Master extra resolution elements are an extension to the core and is only decodable by processors capable of HR or Master decoding. So the optical will only pass the "core" element of the DTS stream. For True HD, there is a hidden Dolby Digital encoding on the disc as well. It may not be selectable from the menu, but if you're using the optical out and select True HD as your audio choice, you'll actually be getting the "hidden" Dolby Digital bitstream.

#3 of 4 Michael Reuben

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Posted August 23 2010 - 04:43 AM

It depends on the player and the settings.


Most players have a setting that will downmix the audio output to 2-channel (i.e., stereo) PCM. For obvious reasons, this isn't the best choice for 5.1 soundtracks.


If you turn off any such downmixing, so that optical output is set to "bitstream" (or whatever term is used in your player's settings), then the result should be as follows:


Dolby TrueHD on Blu-ray is always accompanied by a Dolby Digital compatability track, even if it's hidden and not listed on the disc's menu. As long as the disc is properly mastered, selecting TrueHD will send the compatability track to the optical output.


DTS-HD Master Audio has a standard DTS "core" that the player should be able to extract and send to the optical output.


Depending on the player, there are other settings relating to "Secondary Audio" that may affect these results.

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#4 of 4 Geoff H

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Posted August 23 2010 - 09:01 AM

Good info. Thanks all.