[LAU] Hint for people with no HDMI sound.

[james]

I have a PC with an AMD APU chip, and I'm trying to send sound to my 
Audiolab 8200AP processor over HDMI.

The system is 'Ubuntu Studio 15.10'.

I believe the hardware works - I can boot into Windows 10 and send audio 
from jriver.

With Linux, however:
  - aplay -L does list the hdmi:Generic device, and pulse is using it
  - Pulse Audio volume control does detect whether the HDMI cable is 
plugged in at both ends
  - speaker_test -c 8 -D pulse loops continuously and thinks its playing
  - Pulse Audio volume control shows the ALSA plug-in [speaker-test] stream

However, the Audiolab is stubbornly said the channel is 'silent' on its 
display.

And then I used 'Settings/Display' to select the 'IAG 6"' and select 
'use this display' and to mirror the displays - the computer is actually 
displaying on an attached VGA monitor.

And that made things start to work.

Ideally I would only access the system over xrdp - but you can't enable 
the extra monitor without being on the console.

Quite possibly I would not have had the issue if either the display was 
running through HDMI or the VGA monitor was not plugged in - but it is 
worth bearing in mind if you are having issues.

I guess it would be handy if the display on the volume control could 
indicate 'plugged in but output is inactive' - or (better still) if the 
HDMI output were active if either the display or sound system wants to 
use it, and the display is just an unchanged or black background.