This document provides a timeline of key developments in audio mastering from 1940 to present day, including the invention of vinyl cutters in 1940, tape machines in 1948, multi-track recorders in 1955, stereo in 1957, compact discs in 1982, digital audio workstations in 1995, and MP3 in 1999. It also lists common audio mastering services like raising overall levels, evening out song levels, correcting mixes with equalization, and enhancing flow between tracks.