A Mastering Engineer is one skilled in the practice of taking audio (typically musical content) that has been previously mixed in either the analog or digital domain as mono, stereo, or multichannel formats and preparing it for use in distribution, whether by physical media such as a CD, vinyl record or as some method of streaming audio.
Mastering is something we love doing. The industry typically gives most of the credit for an excellent sounding record to the mix engineer. Still, since we began mastering, we feel a lot of that credit can also go to the mastering engineer. If you listen to a track pre and post-mastering, you will immediately notice that the post-mastered track sounds more like a professional record.