When I online, I really have to pay attention more to audio than at any other time of my editing.  So I use many tools, pens, keyframes, etc.  and a quick way to manipulate the ends of audio is through transitions. If you already know how to add audio transitions (using hotkeys), then you can go the the very last screen shot in this posting to see how the "Duration" and "... On Edit" keyboard shortcuts can be assigned to the keys of your choosing.

For everyone else, if you want to really take control of your audio transitions when editing in Final Cut Pro, you'll need to use some keyboard shortcuts related to those audio transitions, and their alignment on their corresponding cut they cover, and also quickly changing the duration of the transition through a keyboard shortcut as well.

Adding an audio transition, making it the length you want, and aligning it the way you want, are all things that will be done by you.  So why not make use of those keyboard shortcuts for doing all of it!?

Let's start with the one (and usually only) audio transitions you'll need "Audio Favorite Transition #1″ (you can have up to 8 or so, but really, for audio, you probably don't need more than 1 or 2).  You'll need to make sure that you have an audio transition in your Favorites folder for this to work.  (if you've never put a transition/filter in your "Favourites" folder before, here's a quick video to show you how, otherwise you can skip past this video below)