Mastering audio is very different than mixing and involves more complicated steps than just an eq and a compressor. We'll clean up the audible sounds and make them presentable. Most managers and producers set aside 1/3 of the entire recording budget on mastering alone. This is the most important step in the process. A corvette on the assembly line, is still just a bunch of parts bolted together. It isn't until the final stages of paint, polish, tuning, and testing that it finally becomes a corvette.