[mythtv-users] HDMI audio mute/unmute problem

Michael T. Dean mtdean at thirdcontact.com
Mon Oct 13 21:57:59 UTC 2008

On 10/13/2008 05:34 PM, Kirk Bocek wrote:
> Michael T. Dean wrote:
>> You need to fix your audio card configuration in ALSA using alsamixer to 
>> set the right*** switches--the things that many people think are 
>> volumes, but are not, i.e. the ones where people say, "For some stupid 
>> reason I have to set the IEC958 volume to 0 to get output from it--at 
>> 100%, it's quiet...".
> Mike, would you give an example of what you mean by "switches." I'm familiar 
> with alsamixer and am not quite sure what you mean.

They look just like the volume sliders, but they usually only have 2, 3, 
4 or (some other small number) of states (i.e. "0" and "100" or "0", 
"33", "67", and "100" or whatever.  Generally, though, you don't want to 
just start flipping switches, because it's usually a combination of 4 or 
5 switches that need set to specific values to give the behavior you 
want (so testing them all is tricky--especially when you factor in the 
likelihood of having one or more invalid tests during the process, 
especially since you've never seen it work, so you don't know all the 
proper steps for testing whether it works).  So, your best bet is to 
find a good source*** of information on the alsa driver and the card 
you're using.


***Finding a good source of information on anything ALSA related may, in 
fact, be more difficult than testing all the combinations of values for 
all the switches...  Most of the information I have has come from 
searching through tons of poor sources of information, the occasional 
acceptable source of information (generally alsa.opensrc.org ), tons of 
trial and error, and direct examination of the ALSA source. :(  Still, I 
recommend seeking the information rather than blind trial and error.

And, no, I don't have any specific information that could be helpful to 
you.  Sorry.  I just know that there are switches that control settings 
for all the IEC958 status bits--different switches in every card (not 
just in every driver, of course).  I also know that it's possible to 
concoct an ALSA configuration file (i.e. ~/.asoundrc or /etc/asoundrc ) 
that allows you to create a logical device name--"myhdmi", for 
example--that can be used as an ALSA device name and that sets the sound 
card state appropriately (though this is /not/ the approach I'd 
recommend because it takes a /lot/ more effort than just configuring the 
sound card appropriately, as creating the logical device necessarily 
requires knowing the proper sound card configuration and adds the 
additional step of defining the device.  I know this is possible because 
I've done it before (for a different card/driver, of course), but I've 
never posted such ALSA configurations because generalizing them is 
difficult (near impossible) and the simple ALSA configuration I posted, 
which ended up on the wiki, was enough of a pain and--most 
importantly--I'm hoping that soon enough (I'm a patient man) we'll all 
be using OSS4 rather than ALSA for audio in Linux systems.

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