[mythtv-users] Strange Audio Problem 0.25

Igor Cicimov icicimov at gmail.com
Wed Jun 13 04:02:28 UTC 2012


On Wed, Jun 13, 2012 at 1:43 PM, jr <jraymyth at gmail.com> wrote:

> On Tue, Jun 12, 2012 at 11:03 PM, Igor Cicimov <icicimov at gmail.com> wrote:
> > Did you try with "ALSA:hdmi:CARD=NVidia,DEV=3" or DEV=7 in the audio
> setup?
> > Sorry fot top post im typing this on my phone. If not available as
> selection
> > i think you can manually edit it.
> >
>
> Hmmm.  This is confusing.  Using 7 in that line resulted in a no
> device found error.  But it got me wondering, so I went thru all of my
> listed devices with DEV=7, and found one that works.
>
> ALSA:dmix:CARD=NVidia,DEV=7
>
> This is good, but I dont understand why the HDMI line does not.
>
> I have an
> ALSA:hdmi:CARD=NVidia,DEV=0
> ALSA:hdmi:CARD=NVidia,DEV=1*
> ALSA:hdmi:CARD=NVidia,DEV=2
> ALSA:hdmi:CARD=NVidia,DEV=3
>
> *A connection is found by MythTV.  Clicking "Test" yields the test
> hiss in alternating speakers.  No sound when playing a recording.
>
> Also:
> ALSA:hw:CARD=NVidia,DEV=3
> ALSA:hw:CARD=NVidia,DEV=7**
> ALSA:hw:CARD=NVidia,DEV=8
> ALSA:hw:CARD=NVidia,DEV=9
> **A connection is found by MythTV.  Clicking "Test" yields the test
> hiss in alternating speakers.  I hear a fast fluttering sound when
> playing a recording.
>
> Also:
> ALSA:plughw:CARD=NVidia,DEV=3
> ALSA:plughw:CARD=NVidia,DEV=7**
> ALSA:plughw:CARD=NVidia,DEV=8
> ALSA:plughw:CARD=NVidia,DEV=9
> **A connection is found by MythTV.  Clicking "Test" yields the test
> hiss in alternating speakers.  I hear a fast fluttering sound when
> playing a recording.
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>

Yep now that you mentioned it I remembered, the HDMI option was not working
for me too. I think has something to do with the channels, format and
sampling rate which needs to be 48KHz for the digital output (I think).
That's why you need to choose the software mixing plugin device and not the
hardware device it self. Then the dmix plugin probably uses the hardware
device as slave PCM.

So it goes something like this:

# This is the DMIX device you chose and it uses a PCM slave called here
"digital-hdmi"
pcm.dmix {
  type dmix
  ipc_key 1235
  slave {
    pcm "digital-hdmi"
    period_time 0
    period_size 1024
    buffer_size 4096
    rate 48000
  }
}

# This is the hardware device it self, Nvidia HDMI, which is
card=1,device=7 in your case
# and is being used in the above dmix device as slave
pcm.digital-hdmi {
  type hw
  card 1
  device 7
}


Please note that this is from my understanding of how ALSA works :) It's
little bit complicated and I'm sure you can get much better explanation
from some of the audio experts here like Jean-Yves. I would also appreciate
if they correct me if I'm wrong so we both learn something too :)

Igor
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