[mythtv-users] rPi3 3.5mm audio out - HDMI

Barry Martin barry3martin at gmail.com
Sun Oct 22 20:41:30 UTC 2017

Peter and David:

> This amplification will likely not work with HDMI audio, or you may have
> to change some settings to get it to work.
> In my experience, HDMI audio is digital and volume controls either in
> mythtv or in Linux have no effect on volume. If you are seeing [ and ]
> having an effect you may have something set up wrongly.
> Some suggestions -
> - Run alsamixer before starting mythtv and make sure your volume is set
> to maximum on all devices shown.
Verified at 100%/maximum
> - use raspi-config to force HDMI audio
Found the utility; didn't see anything to configure audio.  In 
Preferences there is an Audio Device Settings option (a few above the 
Raspberry Pi Configuration option) and it has a Sound Card selection, of 
which the only option is "bcm2835 ALSA (Alsa mixer) (Default)"  All 
options turned on and set to 100%.

(Please note not trying to be a 'smart-rump': I've got Ubuntu computers 
here which one will have an option and another will not and they were 
configured from the same ISO.)

> - try the digital audio with ALSA instructions, see
> https://www.mythtv.org/wiki/Raspberry_Pi

This reference was very helpful!

> I can't test it right now to give the exact instructions, but
> somewhere in the MythTV audio setup, there is an option for software
> volume control.  When that is enabled and the output audio is digital,
> MythTV will decode the audio, adjust the volume in software and then
> re-encode the audio before sending it out.  Now, this requires some
> level of CPU power to do this, but I believe most current CPUs,
> including the RPi, should be able to do it.

What I found out is both you you were right, depending on the 
configuration in Setup > Audio.   If (page 1) Audio Output Device is set 
for "ALSA:sysdefault:CARD=ALSA" and (page 2) "Use internal volume 
controls" is ticked and 'Mixer device' is set to 'ALSA:default" then the 
[ and ] keys will control the volume, which is handy as the monitor does 
not have a volume control.

If I set to (page 1) to 'ALSA:pluhw:CARD=ALSA,DEV=0' or 'DEV=1' then I 
loose the keyboard control.

Also experimented with the OpenMAX options; didn't seem to make any 
difference and the webpage indicated ALSA was better on the RPi 
experimented more with the ALSA.

So I guess unless we can figure how to increase above 100% (and no 
distortion!) I'll leave things as-is.

Thanks for the assistance!


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