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Discussion Starter · #1 ·
Hi,


ever since I got my HTPC I ran into issues getting a 5.1 sound setup through HDMI, but now I really want to get over it!


All I can get with alsa is stereo, no matter what I play with in the asound.conf. My receiver always sees the connection as stereo unless I use ac3/dts passthrough then all is good.

It works fine in Windows so I know it is not hardware related.


I am testing the sound with speaker-test -twav -c6.


I have read a lot about this issue, and now my only hope seems to lie in the various options we can give in the modprobe conf file, but I cannot find anything for an HDMI connection coming from a radeon card (with radeon driver), and trying all these model options (and the rest) is kind of




Interestingly if I use pulse audio, I get kind of a 3.0 setup, in the sense that the center channel will be used for what it should do in speaker-test, but the 2 other front channels will also be used... Even then the receiver still sees stereo (weird?).


I am running Arch Linux with latest kernel, alsa, etc... not sure what else


uname -a

Linux 2.6.36-ck #1 SMP PREEMPT Mon Nov 22 23:51:09 PST 2010 x86_64 Intel(R) Core(TM) i5 CPU 750 @ 2.67GHz GenuineIntel GNU/Linux


I seemed to have the same issue with catalyst and radeonhd drivers... so the issue seems to lie in ALSA itself but I cannot find any solution...



Thank you!
 

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To the best of my knowledge, the ALSA driver for Radeon cards only supports 2-channel PCM (and DD and DTS passthrough). If you want > 2 channels, I guess you have a few options:


1. Use ac3/dts passthrough

2. Use an nVidia GT210/220/240 video card.

3. Use a soundcard with analog 5.1/7.1 outputs (one that's supported by ALSA, of course).
 

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Discussion Starter · #4 ·
So following your advices I bought some rca-jack cables and 5.1 worked right away with pulse.


2 things though:

- Since it seems the receiver (hk 240) cannot automatically switch between coaxial stream and 6 channels, is it any bad if I don't use the coaxial for passthrough and decode everything on the htpc instead?

- It's still a lot of cable, are you sure about the fact that the alsa driver just won't give more than 2 channels?



Thanks so much!

I was wasting so much time on something I could not get...
 

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No I'm not sure, I could be wrong. But that's my understanding.


Decoding on the HTPC instead of the receiver should be fine, assuming you're happy with the sound quality of the sound card in your PC.


May I ask why you need multichannel LPCM over HDMI, instead of just Dolby Digital or DTS passthrough? Do you have source material with 5.1 surround sound that isn't already in Dolby Digital or DTS?


Also, MythTV 0.24 can re-encode to Dolby Digital on the fly, if need be. I don't know about other media programs.
 

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Discussion Starter · #6 ·
For your question, 2 reasons:

1- I'm a nerd and I like things to work, but you are right I don't really need it. (it was bothering me to always see stereo on my receiver)

2- I do have one movie in true hd that my decoder can not decode, but I could probably do something else... (it seems xbmc that I use can do like mythtv and reencode as well to dts...) so it's mostly 1
 

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If you're watching a movie with a Dolby Digital or DTS surround sound audio track, you shouldn't be seeing "stereo" on your receiver. Are you sure whatever program you're using isn't downmixing to stereo?
 
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