What is mastering?
“Mastering” is the last subjective decision making process in the creation of an album, and is done before “cutting”. Mastering may involve equalization (balancing frequency response), leveling relative amplitude between cuts, adjusting spacing between cuts, using other signal processing devices or software (for adding echo or compression, for example)… in other words, all the last minute adjustments to the music after mixdown of the “master tape”. Adjustments through mastering are typically required, because individual tracks may be recorded at different locations, at different times, using different equipment, different instruments, different players, etc., etc., requiring that the final product have some smoothing done to it to create a more integrated, consistent feeling whole.
Cutting is the last step in production of the physical lacquer, which will ultimately be used to produce vinyl records. During cutting, the master tape is played back, mastering adjustments are applied to the signal, and that signal is then sent to the cutter head.
In the old days, the mastering engineer in the cutting room would put up the master tape and spend the time required to decide what changes were needed to make the final product better. Copious notes were made to indicate all the moves the mastering engineer would have to make each time a lacquer was cut from the master tape (not an eq copy).
Moves would include master volume slides, L & R volume & panning incremental changes, Equalizer and other signal processing settings, etc. Typically, with a lot of moves to make, the engineer would make them during the fade of one song (where they wouldn’t be noticeable), so they’d be in effect at the beginning of the next song.
The master tape would be properly stored (tails out) with the mastering notes included, so another mastering engineer could pull the tape off the shelf and cut parts (following the notes) that were identical to those cut by the original mastering engineer.
The first time(s) lacquers are cut, after approval of acetates (disks that are test cuts and actually played and listened to), an eq tape copy is recorded simultaneously to cutting. These eq copies, which require no further mastering because they already include mastering changes, are sent to other countries for 2nd generation disk cutting there, and are held as backups in case something happens to the master tape.
So the original mastering engineer usually cut the first parts that went into production of the initial vinyl orders. Subsequent runs could have been cut by the original mastering engineer or another engineer in the production process.
Mastering is an art, which requires numerous skills, not the least of which is an above average musical ear. It also requires excellent organization skills in order to make the physical moves while playing the master tape/file, as well as being able to clearly document the process. It requires the ability to effectively operate various types and pieces of physical outboard signal processing equipment and/or software. Actually playing an instrument is helpful as well, as it enhances one’s understanding and feel for the subtleties in music, such as harmonics unique to a particular instrument. And mastering is required whether the final product will be vinyl, CD, tape, DVD, whatever..
In talking about cutting VINYL in my prior posts, I skipped the really boring parts about the geometry of groove depth and width, how it is affected by in/out of phase conditions of the program material, width of the workable lacquer surface, how one can fit more program material on a side by decreasing amplitude, how one can make it look like there is more program material on a side by increasing the space between grooves, how one can hopefully avoid the cutter head lifting off the lacquer during cutting by crossing over low frequencies (which are less directional to the ears) into mono, how one can temporarily expand the space between grooves to avoid hearing a presignal at the beginning of each cut (or after quiet passages) due to possible misshaping of the groove caused by the adjacent groove with signal warping the narrow, quiet groove without signal next to it that was cut on the prior revolution of the table, how material closer to the center of the disk is more susceptible to high frequency distortion due to stylus mistracking because of the lower speed compared to outer grooves, and on and on.
These are all issues the mastering engineer learns techniques to deal with through being taught, by practice, and of course, experience. After mastering test run-throughs, where the tape is played, all mastering moves are made with the lathe running, but the cutter head is not engaged, and the engineer makes any last minute decisions as to disk space considerations, all settings controlling lathe behavior are handled at the console; the engineer does nothing at the lathe until cutting is complete. (I suppose some of the older, less automated lathes required the engineer to push various buttons are turn handles to create lead-ins, lead-outs, and lockout grooves at the beginning and end of sides, and the spaces between songs.)
After cutting, obviously, the engineer spends a good deal of time examining the disk surface through the scope looking for potential problems before sending lacquers to the plating facility. Similarly, the engineer should have spent some time making sure the quality of the lacquer blank was good, avoiding those with obvious surface bubbles or other imperfections. And scoping still does not catch all groove problems. That is the main reason why test pressings are sent to the studio… for playing on typical home style turntables to make sure they don’t skip before large quantities of records are manufactured.