There was a lot of consumer and pro audio press about the introduction of the Mastered for iTunes program, but there are still a lot of music creators and producers who aren’t aware of the program’s details, advantages, or implications.
This article explains the Mastered for iTunes program, and why it’s an important benchmark for digital music in general.
Masters vs Premasters
Like nearly every other digital music distribution channel, iTunes doesn’t really want a master; they want a premaster. The so-called ‘mastering’ process is actually two related, but operationally discrete sub-processes:
Premastering, which encompasses all of the aesthetic decisions related to preparing a set of mixes for an audience. Premastering answers any questions related to what the record is going to sound like.
Mastering, which is the process of creating the delivery media that will allow the audience to access the material. In the case of iTunes, this includes encoding an Apple AAC file and adding the appropriate metadata.
It doesn’t matter if you’re a major label dealing directly with iTunes, or a self-released artist using an aggregator; iTunes wants a specific digital audio premaster so that they can do the encoding (i.e. mastering) in-house.
So what do they want, and how do you know that your master is going to turn out the way you would want it to? That’s precisely what the Mastered for iTunes program is all about.
Codecs & Compensated Premasters
The goal of any digital audio codec is to take a high-resolution or CD-quality digital audio file, and generate an encoded file that retains as much of the subjective audio quality as possible, with a reduced file size.
Regardless of anyone’s opinion of any particular codec, if your music is going to be sold on iTunes, it’s going to be encoded by Apple using their variable bit rate 256kbps AAC-LC encoding format.
This introduces an important issue. Apple AAC is not lossless. This means the sound of the master may be discernably different than the premaster.