Gentner trick: tuning local reinforcement

[Robert Olson]

At HPDC we had to do local reinforcement, and I was running into bad 
problems with feedback if the mic gain was up high enough to drive the 
audio PC. Found the following thing to do to separately control the gain 
fed back to the local speakers:

Do not route mics directly to speakers.
Route mics to Sub Bus 1.
Route Sub Bus 1 to speakers.
Click on the Sub Bus 1 button in the main window and adjust attenuation to 
get the right level into the room.

This goes along with the fix of routing the codec audio to an output, and 
setting that output to be the EC ref (not the speakers). This gets rid of 
the local and remote garbling you'll otherwise see.

See http://www-unix.mcs.anl.gov/~olson/AG/local-reinforce.jpg for a picture 
of this setup.

--bob