This relates to Mumble. The attenuate other applications feature does not work (lowers volume of other applications while someone is talking).
I was wondering if there was native feature built into Ubuntu which can take over this duty.
Suggestions much appreciated.
This is something that has bothered me for quite some time, so I decided to go fix it. :) As of a few minutes ago, support for this has been merged into Mumble for the next release:
https://github.com/mumble-voip/mumble/commit/0e4d963a5a762520945d01a328d17688fb6c2fd8
You can try it now if you're brave and want to run off of git, otherwise you'll need to wait for the next release. I'll keep this answer updated as this progresses.
You should give earcandy a try. It's in the ubuntu repositories, just use the software centre to install it.