I had a couple of requests for more specific information regarding audio quality in mumble, so here I go through a few of the more common audio issues I've run into with a few tips about what you can try to do about them. These issues are: overdriven audio, quiet audio, distorted audio and choppy audio.
Eve bot (http://frymaster.127001.org/mumble) is also mentioned as an alternative to using the loopback settings within mumble for troubleshooting.
Thanks to Peter64 for his help with generating the choppy audio segment.
This is a very brief introduction to the mumble client, highlighting some of the basic options and gotchas involved in setting it up.