o_o "What's that noise?!" "not sure but its probably from Soundtrack pro!"

Soundtrack Pro, is another Apple developed software and is used to make it easy to compose tracks for personal use or film. In the programme there is a 'multi track mode' and an 'audio editing mode.'
In the 'Multi Track Mode' instrument loops and sound effects can be put in sync with he imported video (usually from Final Cut). Here you can also adjust the tempo of the music/sound as well as sometimes being able to change key!

'Audio editing mode' is where sound clips can be edited on their own (http://www.youtube.com/watch?v=cuS1cCnG8xc) ad the frequency spectrum can also be seen (like the picture on the left). Here, the audio can be faded in and out as well as the user being able to add in and take away segments and clips from the already available sound. Sound can also be reversed or normalised as well as reordered! Basically... you can change what you hear!

Once the soundtrack is finished you can export it to final cut and finish editing your movie. Ta daaa!