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Old 3rd December 2007, 08:06 AM   #1
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Default HDMI and digital out

I have done some readings and it appears the HDMI carries LPCM multichannels. If this is the case, we should be able to get the LPCM signal from universal players with SACD and DVD-A functions via HDMI interface.

anyone has any idea whether this may be feasible?
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Old 3rd December 2007, 09:20 AM   #2
sangram is offline sangram  India
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You are correct, it does. I am now watching this thread.

I believe there is DRM involved in demuxing the HDMI signal into audio and video signals.

Keenly interested to see how it is implemented. There is some (somewhat unrelated, and somewhat preliminary) discussion at the Linux thread on decoding at least the audio signal, as it may offer an option to USB and SPDIF.
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Old 3rd December 2007, 09:43 AM   #3
4real is offline 4real  Netherlands
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Default Re: HDMI and digital out

Quote:
Originally posted by ackcheng
If this is the case, we should be able to get the LPCM signal from universal players with SACD and DVD-A functions via HDMI interface.
Do we? I don't think so.... Why? Since HDMI can support MLP, when using DVD-A, it will siply directly stream MLP data via HDMI, and not convert it to LPCM first. SACD is kind of the same, if you hava HDMI 1.2, you will simply have a DSD stream via HDMI, and again: no LPCM. And in case you have an SACD player an no HDMI 1.2 of more, you have: nothing at all...

At least... that's what I think will happen.
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Old 3rd December 2007, 10:07 AM   #4
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I have come across some HDMI to DVI + SPDIF converters on the net. Google for HDMI SPDIF converter. But it doesn't say what is carried in the SPDIF? Not sure if it is only stereo or multichannel

http://www.converters.tv/products/di...rters_431.html
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Old 4th December 2007, 05:01 PM   #5
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I was thinking about this the other day. There are some HDMI receiver chips available at digikey. I started to look through the data sheets - but it was way over my head. Something about TDMS, yada, yada. In theory, it is definitely possible. I played a CD through HDMI to an LCD tv recently. (That's what got me started thinking about it.)
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Old 4th December 2007, 07:13 PM   #6
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You chaps ought to read up on HDCP.
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Old 5th December 2007, 05:10 PM   #7
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Setting aside HDCP that I don't know well, HDMI 1.0 ~ 1.3 can carry PCM, either stereo or multichannel. HDMI 1.1 ~ 1.3 Tx's are allowed to transmit multichannel PCM from DVD-A discs. HDMI 1.2 ~ 1.3 Tx's are allowed to output stereo/multichannel DSD. Unfortunately PCM converted from SACD contents are reportedly prohibited over HDMI link, but some Oppo player does that on HDMI 1.1.
Now HDMI 1.3 Tx's support all the mentioned formats over its link, in addition to that, they can transmit bitstreams of new audio formats for BD/HD-DVD like DD+, DTS-HD and TrueHD.

For clarification, multichannel PCM are transmitted over HDMI for DVD-A playback. For some reason, they didn't put MLP stream on HDMI, and it simplifies the system design by not putting MLP decoder on the A/V receivers and pre/pros.

If you can somehow get HDMI receiver chips or preferrably a boards (since HDMI chips would require some microcontroller intervention to work), getting PCM and DSD would be possible. It would be tricky to apply some processing on the DSD stream if needed, and decoding of new audio formats(even the old legacy formats) would be impossible at DIY level.
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Old 5th December 2007, 05:28 PM   #8
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Quote:
Originally posted by jheoaustin
Setting aside HDCP that I don't know well,
In that case you are unlikely to get very far.
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Old 5th December 2007, 05:42 PM   #9
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Quote:
Originally posted by rfbrw


In that case you are unlikely to get very far.

FYI, I am not going that way.
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Old 5th December 2007, 05:46 PM   #10
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Default Modify a receiver

If you guys want some HDMI receiver for multichannel digital audio, I'd rather go with modifying existing HDMI-equipped AVRs. They are cheap, and have all the input selection and even some decoding capabilities. Hacking the mute and I2S signals from DSP to DAC would be the thing to do. Then probably you can make or find multichannel S/PDIF Tx to get digital audio out of the box, and use multichannel S/PDIF Rx to receive the signals into your DSP or DAC boxes.
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