• New History panel - gives you the ability take waveform and multitrack mixes back to earlier states within the same session just like you can do with graphic edits in Photoshop. Experiment with signal flow though a series of audio effects, try out different surround mixes, or apply a variety of degrees of noise reduction to a track, with the assurance that you can recall your original settings with a single click in the History panel.
Adobe Audition 5.5 has been rewritten from the ground up - they would have had to for the port to the Mac, while retaining the graphics and most of the workflow. Because of this Adobe has been able to make it much more efficient and faster, especially through the use of multicore processors.
Audition is a very comprehensive product and is very ready for professional production work. Now with the ability to work with Adobe Premiere Pro and the fact that it works on the Mac, I think it is going to become the defacto standard for the film, web, and video production world.
Now this doesn't come at some price. With this release, MIDI sequencing, CD burning, and Rewire are all not present. This doesn't mean that some or all of these won't appear in future updates - it just means that they do not exist in this version. It also means that those wanting to upgrade, may choose to wait, or keep version 3 on their systems.
I would have call Adobe Audition 5.5 a revolutionary release in that Adobe appears to be repositioning Audition to replace Soundbooth and take on a potentially larger market. In doing so, I suspect that the development efforts will be radically more frequent in the future. If you are a user of Audition 3, you may want to check out the free trial and also keep your existing copy of Audition installed. If you are a Premiere Pro user, this is a must have upgrade. If you are a new user, I very highly recommend Adobe Audition 5.5