So there's this audio nerd meme starring a promising young ingénue named Scarlett Johansson that perfectly illustrates the three main stages of producing music: before mix, after mix, and after mastering. In each picture, Johansson looks progressively glamorized – an evolution that begins before makeup and ends in a stylized portrait. That is, until the fourth picture – MP3 – that finds the "mastered" photo vulgarly pixilated. So it goes.
Mastering is the final step in getting your album ready for manufacturing. It's a service that’s both practical and mysterious: the former because you'll have to be settled on your mix, the track titles, the running order, the space between songs – the things that make the audio journey complete. The latter because this is where the last bit of sonic polish is applied to your music. Like that stylized portrait, this is where every last detail is put perfectly in place. It's the icing on your aural cake.