Mastering is the process of preparing and transferring recorded audio material from a source containing the final mix to the master, the source from which all copies will be produced (via methods such as pressing, duplication or replication).
Digital masters have become usual although analog masters are still being used by the recording industry.
Mastering requires critical listening and expertise.
Results still depend upon the accuracy of speaker monitors.
Mastering engineers also usually need to apply corrective equalization and dynamic enhancement in order to optimise sound translation on all playback systems.