Basically, if mixing is about ensuring that elements interplay nicely in the context of the song, mastering is the same idea on a higher level – it’s about ensuring your songs sound good in the context of the intended playback media/environment, including other music that’s likely to precede or follow yours.
For example, if you’re releasing an album, part of the mastering process will be to make it cohesive on a song-to-song basis so the whole album has a coherent sound. If you’re releasing on vinyl, the process also involves ensuring the music doesn’t make the record skip and things of that nature. And for digital releases, CDs and so on metadata is added to each song for royalty tracking etc.
For dance music, you want to ensure the music works in a club system and that it sits well with other tracks in the same genre, and for pop you want to ensure your songs sound good together with other pop in as many playback environments as possible.
At a minimum, mastering usually involves making things a bit louder to sit well with commercial releases. Beyond that it really depends on the source material and its intended use cases.
However, the role of the mastering engineer has shifted a bit over the years, as there was less need for the pure engineering aspects such as vinyl compatibility. Nowadays they often also control the final phase of the mixing process, where you’re processing the entire track to make it sound as good as possible as an individual song, outside the context of other music.
There’s plenty of low cost mastering services available. We charge a reasonable flat rate for the service.
