Audio mastering is important for a number of reasons. For one thing it’s a final quality assurance from ideally a second and unique set of ears on your music after the tracking and mixing stages have been accomplished. Audio mastering is often final step of post audio production and a great deal more goes into it than people realize. Most people don’t even understand what is involved with audio mastering beyond simply boosting the volumes, so let’s talk about what goes into it.
Audio mastering first and foremost is about improving the audio. This is accomplished most predominantly through equalization which is an effect either analog or digital which gives you control over the different bands of your complete audio spectrum from low to high.
Boosting or diminishing their presence in the mix overall will yield different results and can be used to positively impact the track and compensate for something it might have been lacking. If you have too much bass presence in your mix then you can diminish its influence by taking away from the low end. Conversely if your mix is lacking in the low end, for instance if you’re recording an instrument which doesn’t have a lot of low frequency like an acoustic guitar recorded high up the neck, then you can augment the low frequency to give that track a stronger presence.
The high end of the spectrum can be boosted slightly to give the track a crisper sound overall but going overboard here can sound too tinny. You can also diminish the influence of the high band at particular frequencies to remove or smooth out grating sibilance sounds in the vocals. The more powerful your EQ plugin, the more detailed you can zoom into your audio spectrum to identify and correct specific frequencies causing issues.
Another important aspect of audio mastering involves the levels of the songs which make up your record. It’s likely that each completed final mix is at a different level than any other track on the record, so the mastering engineer might lay them all out on one long track in their digital audio workstation and use compression and limiters to ensure that each track is at the same volume roughly as that which precedes and follows it.
He or she may also boost the levels of the album as a whole to be more on par with other contemporary records of the day so that when someone listens to your music in a mix of their own with other artists, there are no substantial or noticeable changes in volume.
This has only referred to the audio mastering itself so far, if you want sequencing and a final file or image to be replicated, or in other words you want your music released in a physical format, then what you’re interested in is CD mastering.