We could start with a brass patch, but creating one from scratch will give us a better understanding of the synthesis behind it.
If you're taking deep breaths to make your voice loud enough to let everyone in the audience hear you, it should naturally be less shaky. Like Audacity, GarageBand lets you record sound with an external microphone, work with multiple tracks, add music and sound effects, edit/mix audio, and export projects to shareable formats (such as MP3).
