Audio Mastering is the final polishing step after the mixing process. The stages of mixing and mastering both fall into the category of audio post-production. Audio Mastering from a traditional sense is the process of transferring a collection of mixes into a data-storage that will eventually be used for replication and duplication of vinyl (older days) and compact discs. Today, most audio masters are stored in the digital format.
Although analog masters still exist, the traditional method of storing is gradually going out of fashion and the industry has shifted progressively more to storing in digital form. However, for the exception of few mastering engineers who perform analog mastering, this may still be their preferred choice for storage.
The art of audio mastering should be performed by audio mastering engineers with years of experience and specialty in their craft. It is not recommendable to have your mixing engineer or tracking engineer audio master your recordings even if he is best at what he does. The domain of audio mastering should be left to audio mastering specialists as this is entirely a different skill set.
With the evolution of new technology and modern speakers coupled with the digital age, audio mastering has taken a newer approach over the decades and is merely a process of storing. Over the past 2 decades, modern technological speakers have allowed music recordings to embrace a much wider spectrum of frequency. This has changed the way end-users consume music and the way we listen to music everyday. Simultaneous to this change, audio mastering engineers revolutionized new approaches to audio mastering so as to adapt to the newer trends of modern speakers and the way the world consummate or listen to music and sound.
The goal of audio mastering is to take your finished mixes so that they sonically translate well into various mediums from small to medium and large speakers. Audio Mastering is not a role for the D.I.Y (do-it-yourself) who lack the years of hard lessons and experience audio mastering engineers have endured.