[mythtv-users] why does my digital-out work with nvidia ck804?
mythtv.org at sethdaniel.org
Fri Feb 16 20:11:54 UTC 2007
I spent around 2 hours last night playing with my new motherboard with
built-in soundcard. The motherboard is a Gigabyte GA-M55SLI-S4 and the
sound is an Nvidia CK804 (apparently with the Realtek ALC850 in there
Now, as best I can tell, my digital out works just fine (at least when I
played a DVD it worked). But it doesn't seem to work the way I would
expect it to work.
There is quite a lot of information out there about this sound setup.
On the mythtv site there is this:
I was mostly following some instructions I found on the alsa site:
If I cat /proc/asound/pcm:
00-02: Intel ICH - IEC958 : NVidia CK804 - IEC958 : playback 1
00-01: Intel ICH - MIC ADC : NVidia CK804 - MIC ADC : capture 1
00-00: Intel ICH : NVidia CK804 : playback 1 : capture 1
This suggests to me that the output device I would want to use would be
0,2. However the above link says to use 0,0. Okay. Why? This seems
to contradict everything else I have read.
I downloaded some test dolby digital .wav files that were referenced
from somewhere on the mythtv wiki. I attempted to play them using the
mplayer -ao alsa:device=hw=0.0 -ac hwac3 file.wav
mplayer died saying that it couldn't find the codec for file type 0x1.
(??) I still don't know why this was happening even though I spent
close to two hours trying to get it to work.
I also tried:
mplayer -ao alsa:device=hw=0.0 file.wav
mplayer -ao alsa:device=hw=0.2 file.wav
The former just spits out a lot of noise as you might expect. The
latter does nothing. No sound whatsoever.
mplayer -ao alsa:device=digital file.wav
mplayer -ao alsa:device=hw=digital file.wav
I wasn't sure of the proper syntax, but neither of these produce any
sound. I suspect it's because the digital alias maps to device 0,2
which, as shown earlier, produces no sound.
So I was about to give up when I found a gentoo webpage:
This suggested playing a DVD through mplayer. So I did this:
mplayer dvd:// -ao alsa:device=hw=0.0 -ac hwac3 -aid 128
And whaddayouknow it worked. The Dolby Digital light came on on my
receiver and I verified I was getting discrete sound through my 5.1
So I post this as a potential help to those that might be struggling
with this card. However, I also post to ask:
1) Why do I need to use device 0,0?
2) Why doesn't 0,2 work as it seems that is the device for digital out?
3) Due to the above I can't use the digital or spdif alias. Which just
strikes me as really bizarre.
4) Also, does anyone know why I can't play those Dolby Digital wav
files using mplayer and the hwac3 audio codec?
Perhaps I should just be glad that sound works, but I would like to
understand why this configuration works the way it does so that I can
debug any problems on down the road.
This was all on Ubuntu Edgy with kernel 2.6.17. I have an optical cable
from the SPDIF out on my soundcard to the optical-in on my off-board DD
decoder. I believe it is Alsa 1.0.10.
I also tested playing some ogg files. They work just fine through
I have no .asoundrc or any global alsa configuration file.
Thank you to anyone who bothers to read this. :o)
seth / @sethdaniel.org
Skill without imagination is craftsmanship and gives us many useful objects
such as wickerwork picnic baskets. Imagination without skill gives us modern
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