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distributing multichannel PCM audio from computer to multiple rooms, not quite possible with consumer grade equipment
sergeymen
post Nov 7 2011, 00:44
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Over the past few weeks I've been trying to figure out a way to distribute multichannel PCM audio from my computer to the room where the computer is located (bedroom) AND another room (living room).

Here are some premises:
  1. I previously used S/PDIF to distribute audio, but it doesn't carry multichannel PCM. It will carry compressed multichannel 5.1 audio (Dolby Digital or DTS) but not multichannel PCM.
  2. HDMI is the only consumer-grade interface capable of carrying multichannel LPCM audio (MADI/AES10 can be used for this purpose on professional equipment).
  3. If suitable hardware is available (e.g. video card that can serve video and audio via HDMI out) Windows 7 is able to natively output multichannel PCM via that interface without any special tweaks.
  4. Windows can output multichannel audio via S/PDIF only if suitable hardware and drivers are available to compress (using a lossy codec) its native multichannel PCM output into Dolby Digital or DTS (see point 1 above)
  5. Under windows XP one could output both analog (headphone/speaker jack) and S/PDIF from the computer's soundcard at the same time. Under windows 7 it is not possible, at least not with most sound cards. This is not directly related to what I am talking about, but this is what messed up my existing setup and got me looking for a new one.
So I decided to give HDMI a shot, since it seemed like the most sensible solution:

The setup would be an HDMI signal from the computer's HDMI out (on NVIDIA GeForce GTX 560 Ti video card), to an HDMI splitter, to two receivers (one in the bedroom and one in the living room), and also to the computer monitor in the bedroom. So split three ways. I did not want to hook up the bedroom monitor via the bedroom receiver's HDMI out (splitter -> receiver -> monitor) because like most modern receivers this Marantz NR1402 receiver continuously outputs signal via HDMI, even when there is no signal coming into the receiver from the computer via HDMI. So the effect is that when I turn off my computer the display does not turn off. That is very annoying and affects certain ways in which I use the computer.

Anyway, back to the issue:
Unfortunately, when I hook up my computer's HDMI out to the splitter and then to receiver, Windows 7 displays that the only available HDMI audio modes for this setup are 2channel PCM. When I remove the splitter and connect computer -> receiver -> monitor, then 5.1 and 7.1 modes are available in windows 7 via HDMI.

I am not sure if the splitter is reporting to my computer that it is only capable of handling 2channel PCM, or if the issue is rooted in some kind of HDMI/HDCP miscommunication between the devices involved. But the outcome is that the splitter won't distribute multichannel PCM from my computer.

HDMI approach failed, so going back to S/PDIF:

So HDMI seems a problem. I have a strong feeling that the issues I am seeing are due to HDCP or some other obscure issue with this over-engineered interface. There should exist a simple option similar to S/PDIF for multichannel PCM audio distribution. At this point professional MADI cards seem to be the only option.

So I am giving up on multichannel PCM. The only viable multichannel option is to get a soundcard (e.g. one of those offered by HT Omega) that can encode multichannel audio into DTS or Dolby Digital for output over S/PDIF. These features are called DTS Connect and Dolby Digital Live, respectively. Note that DTS Connect offers a much higher bitrate than Dolby Digital Live and thus should be the preferred option. Both of the codecs are lossy, but I think at 1.5 Mbit/s DTS should be transparent to most if not all listeners.

The S/PDIF output from the computer would then be split out to the different rooms using a distribution amplifier. Haven't tried this yet but should work.

Just wanted to share in case others run into some of the issues I have been having.
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krabapple
post Nov 7 2011, 20:47
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QUOTE (sergeymen @ Nov 6 2011, 19:44) *
Unfortunately, when I hook up my computer's HDMI out to the splitter and then to receiver, Windows 7 displays that the only available HDMI audio modes for this setup are 2channel PCM. When I remove the splitter and connect computer -> receiver -> monitor, then 5.1 and 7.1 modes are available in windows 7 via HDMI.


Have you verified first that the GTX560Ti can output multichannel PCM via HDMI at all?

Some computer implementations of PCM via HDMI are limited to 2 channel. (i'm only familiar with this happening on laptop with integrated soundcards, though)

This post has been edited by krabapple: Nov 7 2011, 20:49
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sergeymen
post Nov 8 2011, 05:53
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QUOTE (krabapple @ Nov 7 2011, 11:47) *
Have you verified first that the GTX560Ti can output multichannel PCM via HDMI at all?

Some computer implementations of PCM via HDMI are limited to 2 channel. (i'm only familiar with this happening on laptop with integrated soundcards, though)


Yes it works fine. I tested it in the "computer -> receiver -> monitor" configuration (without the splitter). In other words directly from the GTX560Ti video card HDMI out to the receiver. I confirmed that indeed 5.1 works (I tested positional audio coming from front left, rear right etc). The receiver reported PCM input.
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Arnold B. Kruege...
post Nov 9 2011, 15:26
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QUOTE (sergeymen @ Nov 7 2011, 23:53) *
QUOTE (krabapple @ Nov 7 2011, 11:47) *
Have you verified first that the GTX560Ti can output multichannel PCM via HDMI at all?

Some computer implementations of PCM via HDMI are limited to 2 channel. (i'm only familiar with this happening on laptop with integrated soundcards, though)


Yes it works fine. I tested it in the "computer -> receiver -> monitor" configuration (without the splitter). In other words directly from the GTX560Ti video card HDMI out to the receiver. I confirmed that indeed 5.1 works (I tested positional audio coming from front left, rear right etc). The receiver reported PCM input.


Try a different splitter. It sounds like yours is not reporting back the full capabilities of the input of the next device in the chain. It's probably reporting back nothing, and your source is presuming that it is minimal.
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