Sometimes, especially when merging clips, you get more audio tracks in a Final Cut Pro timeline than you want. This article describes a couple of different ways you can get rid of them.
A while ago, I wrote about how and why to create submixes in Soundtrack Pro. While submixes can be used for reverb, a better way is to use Sends and Busses. This provides greater control and more flexibility than a Submix, but it is a bit trickier to understand.