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 repsect 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.

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.

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 would be used which would be considered transparent and corrective only.

Compression

The second most common type of processing applied would be compression. Again this can be done both digitally and with analog. Units like the SSL buss compressor are popular for imparting a distinct sound to the mixes when appropriate. Compressing can 'gel' or 'glue' a mix together and make it seem more whole. This is a result of the transients being reduced and tightening up of the dynamics of the mix. Perhaps the snare and kick were poking out of the mix a little, compression can tame them making the mix more cohesive.

Multiband

Multiband processing is very popular now especially in plugin form. This allows compression of certain bands only. This is a good way to fix problems in the mix without affecting other areas. If the kick and bassline were too prominent they could be compressed while allowing the rest of the mix to breath. Similarly if the top end is too harsh in places then multiband can be used to only affect those areas needed.

Getting wide

The third major area looked at in mastering is width. By manipulating the stereo and mono components of a mix the sound can be widened making it seem more 3D. Again multiband processing can be used here to affect only certain areas of the mix. Care has to be taken in order to not over do this to the point of phase problems. In this case if too much widening happens then when the mix is played on a mono system certain parts of the mix might cancel out and not be heard.

Here's some general tips on preparing a song for mastering:

Top 10 Audio Mastering Tips For Preparation of Mastering

1. Make sure to leave about 2 or 3 decibels of headroom so no clipping has occurred.

2. Avoiding using too much processing on the master buss.

3. In regards to the above it's ok to mix with some stereo compression and limiting to get a feel for how the track will sound when mastered

4. Give your ears a break so they don't adjust to the music too much.

5. Moniter at comfortable volumes. This can help with the above issue.

6. Check the mix at very low levels. This helps get an overall picture of the mix. Nothing should disappear with these lower listening levels.

7. Don't overuse stereo expanders: They can cause phasing problems if applied too heavily.

8. Reference other mixes.

9. Listen to the mix in a variety of listening environments as well as headphones. Laptop speakers are good for hearing the mix on less capable speakers.

10. If possible allow a few days between mixing and again after mastering to see the mix in a better light.

Conclusion

When all is said and done the finished master should be pleasurable to listen to on a variety of playback systems. This includes headphones, computer speakers, car radio, home stereo and in many cases also club systems. When a mix translates across all of these areas then the mastering job should be considered a success.