Adobe Creative Suite 5.5 Master Collection and Production Premium editions include Adobe Audition CS5.5, which is a much more powerful audio editing application than was Adobe Soundbooth, included in previous versions.
Adobe Premiere Pro CS5.5 includes an Edit In Adobe Audition command, which you can use to send individual clips, entire sequences, or just the selected work area—complete with reference video—directly to Adobe Audition for audio editing and sweetening. If you send an individual clip, Audition uses a render-and-replace process to automatically update the audio clip in Adobe Premiere Pro. If you send a sequence, you can choose to place the rendered audio in the audio track of your choice.
See this video on the Video2Brain website for a demonstration and explanation of this feature.
This video from Jason Levine also gives an overview of this feature.
For more information about using Audition with Adobe Premiere Pro, see “Working with video applications” in the Audition CS5.5 Help document and “Editing audio in Adobe Audition” in the Adobe Premiere Pro Help document.
For complete details of what’s new and changed in Adobe Premiere Pro CS5.5, see this page.