Mastering and Pre-mastering

When we complete a recording project, including the mixing of all the tunes on the project, the next step is to prepare those various mixes for their intended release format, usually Compact Disc. The process for doing this is called mastering, and it is generally considered to be the last “creative” stage in the music production process. Everything after that is intended to be “clones,” to the extent that is possible.

When the release medium was vinyl LPs, the process of mastering was the process of cutting a master lacquer disc on a lathe, in real time, while making the adjustments to the master tape that were necessary to make that recording work on vinyl. People who did this were called mastering engineers. The master tape that they worked with was usually fully mixed and edited by the client beforehand. Changes would include EQ to correct for monitoring deficiencies, compression and limiting to protect the cutter head and limit stylus velocities. Further, often, stereo signals were run through a shuffler and the A-B low frequencies were rolled off to minimize vertical stylus excursions.

With the advent of the CD, this process has changed a little. The mastering stage – the preparation of the “glass master” at the CD factory – is now separate from the preparatory work of final EQ, compression, etc. So what we now call “mastering” is actually part of the process that used to be called “pre-mastering,” which includes all of the evaluative study and trial processing that precedes the creation of the “pre-master tape,” the recording that will be used to create the glass master, hopefully an exact clone. Happily, the glass master is a lot less tricky to prepare than the lacquer LP master was. The CD process is considerably more robust, believe it or not.

At the same time, clients have turned over more of the final “pre-mastering” process to the mastering engineer, including assembly editing (and, sometimes, choice of mixes!) and levels management. This involves the modern mastering engineer quite fully in the creative end-game of recording – the mastering role becomes a critically important one.

There is more – the mastering engineer prepares lots of recordings for release in various media, and has a well-developed sense of how “sounds of the studio” translate into recordings for the masses. In this regard, mastering engineers function as “ears of last resort” – they evaluate the master tapes and determine what will be needed to make it sound to the end listeners as the client producer desires. In this regard, the mastering engineer acts as a correcting agent, adapting the producer’s vision to the realities of the marketplace with its dizzying array of end-users.

How do mastering engineers ply their craft? What do they do? What are their specific concerns? While I do a moderate amount of pre-mastering, I definitely don’t regard myself as a mastering engineer. So, I consulted with Laurie Flannery, of Northeastern Digital in Southborough, MA, who does this all day long for a broad range of clients.[1]

First, let’s look at the tools that are used in mastering.