The Basics of Audio Mastering

What is audio mastering? There's quite a lot of opinions on what it means exactly so let's look at the general process music production.

After the mixdown
After a track is mixed it is generally sent off to a mastering studio to put the finishing touches. Most mixes come in at less than 100% of their potential so it's the mastering engineers job to correct any mistakes as well as 'sweeten' the mix. Done correctly this should give the track the right balance in frequency content, width, dynamics and of course in this day and age, loudness.

Depending on the state of the mixdown the mastering applied can be both corrective and enhancement oriented. Hopefully it's the latter more than the former. When correcting must be done there is a balance that must be made. Any change in one aspect of the mix generally affects another. For instance if a vocal is not clear enough some eq might be added to bring it out. In turn though this could cause other elements in the mix to stand out too much. In this respect there is always a give and take.

Comparison to other tracks
Another aim in mastering is to make sure the finished song stands up against its peers when played side by side. This is the primary cause of the 'loudness war' as each artist feels the need to compete with other artists level of loudness. This has led to an escalation of loudness levels to the point where music is crushed in the pursuit of higher levels.

Audio Mastering Tools:

Hardware or software?
Some of the tools used for mastering range from digital plugins to old vintage gear. There's always a good debate on the merits of both, especially whether or not digital can stack up. Well known high end digital hardware units like the Weiss EQ-1LP are regarded as superb digital eqs, employing linear phase eq methods. Compressors such as SSL, Neve, and Manley might be used in the analog domain while their digitally emulated counterparts exist in plugin format.

Listening tools
Beyond these tools is the need for an acoustically suited room and monitoring system. And finally of course the most import tool is the ears and experience of the engineer.

Techniques for Audio Mastering

Equalization
Most of the basic techniques for audio mastering are similar to the mix process itself. The track is evaluated to identify any problems first. If these are frequency related then a common method is to use equalization to re-balance the frequency spectrum until it is considered even. Due to either the ears, room, or monitors of the person mixing the track there could be too much or too little low end.

In this case the mastering engineer can boost the low frequencies. Often the mastering engineer will have access to much better sounding Eq. In this case the re-balancing can also result in a sweeter sound. Other times linear phase eq