Mastering for vinyl has two functions. One is to optimize a recording for the particular requirements of the vinyl medium. The other is to maximize the sound quality and make all the tracks on the disc compatible in terms of level and EQ.
Vinyl is very much an imperfect medium and has a number of significant limitations:
- Noise due to surface irregularities, scratches, and rumble from the turntable
- The inertia of the stylus limits the extent to which it can accelerate
- The stylus may mistrack (meaning to lose contact with the groove walls)
- The duration per side is limited
- The relative speed between stylus and groove is high at the outer edge of the disc, low in the center.
This means that the mastering engineer has several problems to overcome even before starting to work on the subjective quality of the sound. These problems are potentially so serious that if something was not done properly, a record could be manufactured in quantity and only then might it be found that no-one could play the record without the stylus jumping out of the groove. And yes, this has happened.
Other problems may not be so serious but cause distortion on playback, or cause the stylus to wear out the record even after just a few plays. OK, so some records will maybe only get a few plays during their brief span of popularity, but it is certainly wise to consider the long term.
The art of mastering even for CD and digital media is founded in vinyl and any modern mastering engineer would be working from this tradition. It is certain that a good mastering engineer builds up so much experience in taking people's mixes and turning them into records that only someone working on a very tight budget would ever want to undertake the mastering process themselves. Unfortunately too many people do, only to save maybe $500, which would be a small proportion of the proceeds from any even modestly successful record.