Mastering can vary greatly depending on the source material. Each piece of audio will have its own unique issues and elements that need to addressed.
The full process can involve equalisation, de-essing, de-clicking, noise reduction, phase correction, stereo width adjustment, balance correction, addition of ambience, peak limiting and dynamic expansion or compression.
Files may then be transferred to the customer at this stage or if required audio may then be sequenced with any required fades or crossfades and PQ points encoded (track start and end).
ISRC Codes and CD Text can also be added before a final master is created, usually in the form of a DDP Image.