When you edit your audio clips—adding effects, adding fading, or adjusting the balance, for example—the changes are not applied to the clips, but are stored separately. This allows you to easily undo the changes if you change your mind.

If you are happy with the changes you have made to the audio clip, you can integrate them into the audio clip by flattening the clip. When you flatten an audio clip, Sound Editor does not replace the existing clip with the changed clip, but creates a new copy of the audio clip, with the edits applied.