This is a complex process, as a result of which each audio track of a multitrack (project of a composition by tracks) is processed by various software or hardware instruments, taking into account many factors, in order to create harmony and balance of all instruments in the track. Mixing consists in obtaining at the output a composition that does not have frequency conflicts, interference, noise, and also has optimal dynamics, “transparency”, volume and plans. Roughly speaking, this is giving the composition a “commercial sound” and the most accurate embodiment of the creative intention.
Mastering is the final stage of work on a track, its final cutting. The sound engineer eliminates minor flaws that have arisen at the stage of recording and mixing, and the recording adjusts for reproduction from different media. As a result of mastering, your track will be completely ready for release.
Stem mastering is a separate type of mastering, of a more subtle nature, when you can make adjustments only to a specific element of the track, be it vocals, guitar, keys, etc., without affecting the rest. This gives a better result than mastering a single, mixed composition.