Mastering

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). Recently, the format choice includes using digital masters although analog masters, such as audio tapes, are still being used by the manufacturing industry and by a few engineers who have chosen to specialize in analog mastering. In order to make a deterministic process, mastering requires critical listening; therefore, it cannot be achieved without the presence of a mastering engineer. There are software mastering tools available to facilitate this last step, but results still depend upon the accuracy of speaker monitors. In addition, "music mastering" engineers may also need to apply corrective equalization and dynamic enhancement in order to improve upon sound translation on all playback systems.

History Pre-1940s

In the earliest days of the recording industry, all phases of the recording and mastering process were entirely achieved by mechanical processes. Performers sang and/or played into a large acoustic horn and the master recording was created by the direct transfer of acoustic energy from the diaphragm of the recording horn to the mastering lathe, which was typically located in an adjoining room. The cutting head, driven by the energy transferred from the horn, inscribed a modulated groove into the surface of a rotating cylinder or disc. These masters were usually made from either a soft metal alloy or from wax; this gave rise to the colloquial term waxing, referring to the cutting of a record. After the introduction of the microphone and electronic amplification in the mid-1920s, the mastering process became electro-mechanical, and electrically driven mastering lathes came into use for cutting master discs (the cylinder format by then having been superseded).

However, until the introduction of tape recording, master recordings were almost always cut direct-to-disc. Artists performed live in a specially designed studio and as the performance was underway, the signal was routed from the microphones via a mixing desk in the studio control room to the mastering lathe, where the disc was cut in real time. Only a small minority of recordings were mastered using previously recorded material sourced from other discs.Advances The recording industry was revolutionized by the introduction of magnetic tape in the late 1940s, which enabled master discs to be cut separately in time and space from the actual recording process. Although tape and other technical advances dramatically improved audio quality of commercial recordings in the post-war years, the basic constraints of the electro-mechanical mastering process remained, and the inherent physical limitations of the main commercial recording media—the 78 rpm disc and the later 7-inch 45 rpm single and the 33-1/3 rpm LP record—meant that the audio quality, dynamic range, and running time of master discs were still limited compared to later media such as the compact disc.

Running times were constrained by the diameter of the disc and the density with which grooves could be inscribed on the surface without cutting into each other. Dynamic range was also limited by the fact that if the signal level coming from the master tape was too high, the highly sensitive cutting head might jump off the surface of the disc during the cutting process. From the 1950s until the advent of digital recording in the late 1970s, the mastering process typically went through several stages. Once the studio recording on multi-track tape was complete, a final mix was prepared and dubbed down to the master tape, usually either a single-track mono or two-track stereo tape.

Prior to the cutting of the master disc, the master tape was often subjected to further electronic treatment by a specialist mastering engineer. After the advent of tape it was found that especially for pop recordings, master recordings could be made so that the resulting record would sound better. This was done by making fine adjustments to the amplitude of sound at different frequency bands (equalization) prior to the cutting of the master disc. Record mastering became a highly prized and skilled craft, and it was widely recognized that good mastering could make or break a commercial pop recording. As a result, during the peak years of the pop music boom from the 1950s to the 1980s, the best mastering engineers were in high demand. In large recording companies such as EMI, the mastering process was usually controlled by specialist staff technicians who were conservative in their work practices. These big companies were often reluctant to make changes to their recording and production processes—for example, EMI was very slow in taking up innovations in multi-track recording and they did not install 8-track recorders in their Abbey Road Studios until the late 1960s, more than a decade after the first commercial 8-track recorders were installed by American independent studios.