The process of mastering is one that you will hear musicians rave on about, and anyone else has a rather blank expression when you mention it. This therefore is a brief summary of what it is, and why its done. Hopefully I will get round to writing some articles on how to do it later.
Why its done
If you have ever recorded or produced something and compared it to a professional track, of any genre, you may be surprised at the fact that your track appears to be at a different volume. The same can be seen with television advertising, you can be merrily watching a program until the adverts come on and you are pouncing for the remote to turn it down. Both these affects are down to a process known generally as mastering. Mastering has many other benefits but in modern media this is the main goal when doing it, simply because the human brain links louder to better, or certainly more noticeable.
Now at this point I should explain that the limit for an digital audio file is 0db. Imagine this as your ceiling, the wave that the audio file describes can only be so high (an audio signal is a wave, the higher the wave, the greater the amplitude, the more noise). So if you record/produce a track that is ‘clipping’, the track you are making is hitting this 0db limit, and since it can’t go past this limit, it just stays at 0db until the signal reduces. This, if bad enough will create a clicking sound, more noticeable on large or hi-fi sound systems.
What it does
So, if your track can only get to a certain limit, how can one be louder than the other? In short, because the ear is much more intelligent/dumb than the level meter on your software or hardware. The ear responds to the general level of a track, not the momentary loudness of a certain bit. So if you have a drum beat that peaks at 0db but a quite track otherwise, the ear will hear the quite track, not the loud drum. To get the loudest track therefore you have to have every part of the track just hitting 0db, the ear then hears a very loud track.
But keep reading, as I was careful not to say that this is all mastering is about. The approach above on its own gives you a loud sound that isn’t very pleasant to listen to. Another major part of mastering is to ‘clean out’ frequency bands. If you record/produce two tracks that have the same pitch (frequency) as one another, you will find that they both start sounding a little ‘muddy’, and the fidelity in the track is lost. A common example of this is the interaction between you bass line and your bass drum. Mastering should separate these tracks so you can hear them individually (commonly called a ‘transparent’ mix).
So the addition of both these ideas brings you a mix that sounds loud but also crystal clear, people are paid many thousands to achieve this goal, simply because it isn’t easy, and there isn’t any software that does it for you.