Mastering, a form of audio post production, is the process of preparing and transferring recorded audio from a source containing the final mix to a data storage device (the master), the source from which all copies will be produced (via methods such as pressing, duplication or replication). In recent years digital masters have become usual, although analog masters—such as audio tapes—are still being used by the manufacturing industry, particularly by a few engineers who specialize in analog mastering.

Mastering requires critical listening; however, software tools exist to facilitate the process. Results depend upon the intent of the engineer, the skills of the engineer, the accuracy of the speaker monitors, and the listening environment. Mastering engineers often apply equalization and dynamic range compression in order to optimize sound translation on all playback systems. It is standard practice to make a copy of a master recording—known as a safety copy—in case the master is lost, damaged or stolen.