Apple Soundtrack Pro 3 - Manual (Page 190)

In Soundtrack Pro, actions and process menu operations are not applied directly to a clip,
but to an audio file project Soundtrack Pro creates that is shared by all clips referencing
the original source media. This means that you can apply common cleanup
operations—such as noise reduction—to a single source media file that is referenced by
multiple clips. If you need to apply actions to a single, specific instance of a clip, you must
make an independent copy of that clip. For more information, see
Making an Independent
Copy of a Clip .
Multitrack Timeline before an edit is made
190 Chapter 7 Editing Audio in the Multitrack Timeline