Mastering is part art and part science. It is the last step of production to be done to a song or album before it's sent out for distribution. Contrary to popular belief, a properly mastered song does not only sound louder. A mastering engineer has a keen ear for the minute acoustic details in music.
Because each song is different, the steps involved in the mastering process vary from song to song. Equalization, compression, expansion, limiting, noise reduction, and balancing are some of the post-production processes said mastering engineer may apply to a song. If you are looking to be on par with the professionals, audio mastering is definitely something you should consider to take your music to the next level.