iZotope Ozone is an acclaimed audio mastering package with a chain of multiband dynamics, EQ and other processors with integrated spectrum analysis. It's one of the most complex and effective tools for working with sounds and music.
The interface looks pretty with its soothing dark palette, but can be hard to grasp if you're a beginner. It's a modular setup, with each module being freely movable. Default arrangement and the purpose of those modules may be confusing at first. However, if you get the hang of it, you have access to numerous features and functions like stereo adjustment, mid/side and left/right navigation, undoing history, clear graphical feedback of levels, frequency spectrum and processing. You can drastically change the quality of uploaded audio files, with even the tools like adjustable dynamics detection filter, dynamics parallel processing, matching EQ mode, analogue and digital EQ phase response (with fully adjustable phase for the latter), and Alt-Solo, an EQ frequency pinpointing system.
The program's performance is quite satisfactory. iZotope Ozone works rather fast for such an extensive toolset, the menus and windows do not freeze or slow you down, and it's an overall comfortable experience. There are numerous technical details I could describe, but this would take a more thorough article for consummate professionals. Here, I can only tell that it's big, it's reliable, and it does a great job.