[mythtv-users] All sound out S/PDIF

Bob Sully rcs at malibyte.net
Mon May 19 03:39:58 UTC 2008

>> Right now, I still have to exit mythfrontend and run "iecset audio 0",
>> then restart the frontend to play a stereo recording if I have watched a
>> 5.1 show before it.
> That's due to a misconfiguration of your audio system.
> It has nothing to do with Myth.  It's completely an audio configuration
> issue.
> System configuration bug.  :)

I am perfectly willing to agree with you.  On my frontend box I
occasionally run into similar issues *outside* of Myth as well.  The rub
is figuring out WHERE the configuration bug is.

> Bob,
> I have to agree with Mike: this sounds more like a problem with system
> configuration, perhaps even the driver for your sound card. I do exactly
> what you are trying to do without any modifications to ALSA's
> configuration with a Realtek ALC850 codec (nVidia CK8S on-board audio).
> I would suggest posting to the alsa-users mailing list (check
> www.alsa-project.org); I /read/ alsa-devel daily and if it is any
> indication of what alsa-users is like, the developers/moderators are
> very knowledgeable (duh :) ) and helpful and should be able to point you
> in the right direction.
> Cheers,
> Jesse Burt

I have subscribed to and posted a message to the alsa-users list about
this.  I went through the past several months' worth of archives on both
it and the devs' mailing list without finding anything useful...hopefully
someone there will have run into this before.

> I recently just ran into this exact same issue.  I don't know why, but
> after I upgraded to .21, (and alsa, and my kernel, and a bunch of stuff)
> only the digital passthrough stuff worked.  I'm on gentoo and found a
> file named /etc/asound.names.  In it I found device names that I didn't
> see through the typical aplay -L.   One was named plug:spdif.  After
> going through line by line on the names running aplay -D <name>
> /usr/share/sounds/alsa/Noise.wav (an analog file).  I finally heard
> sound when I used plug:spdif.  So, in MythFrontend, I changed the
> default alsa device from ALSA:default to ALSA:plug:spdif and now
> everything works perfectly.

> David,
>    I'd like to know more about this. I've been around alsa a long time
> and I've never heard of /etc/asound.names. I'm also a Gentoo user and
> none of my machines (8 in total) have this file so it being on your
> system is a surprise to me. I know of /etc/asound.state. Did you
> possibly mean that file?
>    I think the intended method to get a list of devices or PCMs is to
> use aplay -l or aplay -L
> However this doesn't show that my system has any PCMs so I'm very
> curious as to how we are getting different results. Have you set up a
> virtual device under Alsa and you're getting something that way?
> Thanks,
> Mark

> Message: 18
> Date: Sun, 18 May 2008 12:25:34 -0600
> From: David Snider <dsnider at thesniderpad.com>
> Subject: Re: [mythtv-users] All sound out S/PDIF
> To: Discussion about mythtv <mythtv-users at mythtv.org>
> Message-ID: <4830749E.7070805 at thesniderpad.com>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed

> Nope, it's definetly /etc/asound.names.   This machine has historically
> had problems with the spdif out it's an ASUS M2NPV-VM.   In my
> troubleshooting steps, I actually updated to the 2.6.25 kernel and
> asound.names magically showed up.   I just checked my other system
> running 2.6.24 and it does NOT have the /etc/asound.names.  But I also
> had to put the ALSA;plug:spdif setting in the frontend.   Both of them
> are using the optical out directly to my receiver.
>  From my 2.6.25 machine:
> root at noir ~
> # ls -l /etc/asound*
> -rw-r--r-- 1 root root 2462 May 16 11:23 /etc/asound.names
> -rw-r--r-- 1 root root 7833 May 16 10:53 /etc/asound.state
> root at noir ~
> # cat /etc/asound.names
> ctl {
>         alsactl1 {
>                 name hw:0
>                 comment 'Physical Device - HDA NVidia at 0xfe024000 irq
> 20'
>         }
>         alsactl2 {
>                 name hw:1
>                 comment 'Physical Device - MPU-401 UART at 0x330, irq 10'
>         }
> }
> pcm {
>         alsactl1 {
>                 name default:0
>                 comment 'Abstract Device - Default Device (Duplex)'
>         }
> --snip--
>         alsactl14 {
>                 name plug:surround71:0
>                 comment 'Abstract Device With Conversions - Front, Rear,
> Side, Center and Woofer (Duplex)'
>         }
>         alsactl15 {
>                 name spdif:0
>                 comment 'Abstract Device - S/PDIF (IEC958) Optical or
> Coaxial Wire (Playback)'
>         }
> Here is the entry-->        alsactl16 {
> Here is the entry-->                name plug:spdif:0
> Here is the entry-->                comment 'Abstract Device With
> Conversions - S/PDIF (IEC958) Optical or Coaxial Wire (Playback)'
> Here is the entry-->        }
> }
> --snip--
> }

> sudo /usr/sbin/alsactl names

This appears to be a new wrinkle in 2.6.25 (and maybe alsa 1.0.16?)  My
BE/FE runs a custom-compiled 2.6.22 kernel and my FE machine runs 2.6.24
(the stock Ubuntu Hardy kernel - 2.6.24-16 at this point).  The
asound.names file on the Ubuntu box has a few basic entries (nothing like
the one above) and doesn't exist at all on the Mandriva box.

"alsactl names" doesn't return anything on either machine.

Bob Sully - Simi Valley, California, USA

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