[mythtv-users] Upgraded to .20 fixes (14172), have weird digital TV sound issue

Michael T. Dean mtdean at thirdcontact.com
Fri Aug 17 01:44:51 UTC 2007

On 08/16/2007 03:38 AM, Justin The Cynical wrote:
> Michael T. Dean wrote:
>> On 08/15/2007 06:00 AM, Justin The Cynical wrote:
>>> I.e. for AC3/DTS is should open the iec958 device.
>> Passthrough output device
>>> For PCM (stereo or mono) it should open the plug:iec958 device.
>> Audio output device
>>> Try that.  I'm going to try to test it tomorrow morning.
>>> Either way, I've submitted a bug report.  :-)
>> It's not a Myth problem.  It's an ALSA config/Myth config problem.
> Well, my results from this morning:
> Changing the default output device from ALSA:Default to ALSA:plug:iec958 
> worked.  I have sound on all stations and mythmusic going to /dev/dsp is 
> working fine as well (I may try pointing music to the plug:iec958 for 
> giggles to avoid that damned Optical Raw setting on the SB Live card).
> As for the idea of an ALSA config problem:  I did look at that 
> possibility as well, but considering I'm running the asound.conf that is 
> listed in the wiki with a SB Live 5.1, I'm having problems seeing it as 
> ALSA having the problem and not just Myth.
> I'm not claiming to know everything about how Myth interacts with ALSA, 
> and I have been wrong before, but when I'm using pretty much the 
> 'standard' for Myth and digital sound output, well....  :-)

The ALSA response to which you linked said it was a Myth problem because
Myth should have different devices for passthrough and for PCM.  It
does.  Therefore, the problem you're experiencing is a Myth
configuration problem--the Myth configuration of your audio devices is
incorrect, meaning that you've specified the wrong ALSA configuration to
use for the audio devices.  I.e. using ALSA:iec958 is one ALSA
configuration and ALSA:plug:iec958 is a different ALSA configuration. 
Both configurations completely bypass your ALSA configuration file, so
it is not an ALSA configuration file (~/.asoundrc or /etc/asound.conf)

Set up your audio as I've specified above--with plug for the audio
output device and without plug for the passthrough output device, and
all will generally be well, whether using passthrough or not.


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