While not as glamorous as recording or mixing, mastering is most definitely a creative act. Mastering Engineers need to have excellent ears, strong musical instincts, and strong familiarity with a wide range of musical styles. A Mastering Engineer is, among other things, a fresh set of experienced ears to help make the final product as good as it can be. By sculpting each song with EQ and compression, and carefully assembling the entire CD, he can create a satisfying, cohesive project out of the individual elements.
Like most music production stages, Mastering has its creative restrictions too. When mastering a project, a Mastering Engineer is usually servicing the original mixes. Mastering isn't about totally changing the sound of a mix; a Mastering Engineer must remember that someone liked the way it sounds. That's why they approved it, and sent it to the Mastering Engineer for Mastering. His responsibility, then, is to bring out the best in that mix, not change its character completely. While there are some cases when the Mastering Engineer must "rescue" a bad mix, this isn't really part of the job. Despite the running joke among engineers, "we'll fix it in the mix"; Mastering is supposed to be about improving a good mix, not fixing a bad one.
Mastering is simultaneously the last step in the creative process and the first step in the manufacturing process. Mastering is about the creation of a final product. In CD Mastering, you collect the final music mixes that make up the product (the CD), and adjust them so that they all sound like they belong together on the same CD. These adjustments might include:
In much of our industry, the term Mastering is also used when referring to the act of taking one mix, all by itself, and adding a little EQ, compression, and so forth, just to make it sound better. Technically, that's not true Mastering, since there's no element of assembling a final product or creating a delivery Master. Mastering is really about the assembly of a fixed, final product from a large set of assets, like ten or twelve final mixes of songs.