Mastering for vinyl vs. mastering for CD
Mastering is the process that comes after mixing a multitrack recording into stereo. In professional work, mastering is done by a specialist mastering engineer. It is widely thought, usually correctly, that mix engineers who venture to 'master' their work are stirring up trouble, possibly creating additional work for the real mastering engineer later on.
Mastering in the days of vinyl involved manipulating the audio so that it fell within the capabilities of the vinyl medium to store and reproduce.
For instance, excessive low frequency level causes wide 'excursions' of the groove, which limit the playing time of the record. Any out-of-phase low frequency information additionally can make the groove shallow, to the point where the playback stylus might not be able to follow it. Excessive high frequency energy can make a groove that is impossible for the playback stylus to react to. This causes distortion, and damages the groove leading to an increase in distortion on repeated plays.
The principal difference between CD and vinyl mastering is that CD doesn't have any technical limitations. Anything you can record onto disk or tape (analog or digital) can be transferred to CD with no problem.
The only technical issues are these:
- The recording must at some point have a peak level within 2 dB of full scale (higher therefore than -2 dBFS). If this is not so, then the factory will be entitled to reject the master
- The maximum duration is 74 minutes. Some factories will manufacture discs up to 80 minutes. However there may be more rejects, and some players may not play the discs properly
- In the process of PQ coding, the first track must be preceded by a gap of two seconds. The mastering software may do this automatically.
Other than that... do what you like!
The artistic issues are very similar to vinyl, and are these:
- In popular music it is generally considered essential to achieve a high subjective level (i.e. LOUD!)
- The tracks on an album should have a subjectively compatible sound in terms of level and EQ
- In classical music, it may be useful to lower occasional peaks in the recording, so that the average level can be louder and more suitable for listening in the domestic environment
- If it is considered desirable to achieve loud bass, then low frequencies should be in mono so that they will be reproduced by both loudspeakers. Two loudspeakers can obviously produce a greater sound level than just one.
Mastering is widely regarded as one of the 'voodoo arts' of audio. The mix engineer is responsible for creating a great mix from the original multitrack recordings, but it is the mastering engineer who turns that mix into something that really sounds like a record.