From internet forums to music magazines, the term "mastering" is one of somewhat mythical proportions–the final step to end all of your problems and to give you that "BIG, major-label sound (!!!)" Mastering is important and it is the final step, but any respectable mastering engineer will tell you that mastering is not a substitute for a good mix.
Mastering can, however, take a mix from good to great:
Before clip raised in volume for more accurate comparison. Hear more from Ben Talmi on his Bandcamp page.
The most important thing to understand is this: a mix engineer applies effects and level changes to each individual instrument separately. A mastering engineer can only apply effects to everything in a mix at the same time.*
For example, a mastering engineer can't add echo to the vocal without adding echo to all the other instruments in the song too. So what's the point of mastering, anyway?
Mastering serves as a 'glue' to your mix by making overall changes. The main goal of mastering is to match the overall loudness and frequency balance (bass, treble and mid range) to A) your favorite professional (or amateur!) recordings and B) the other songs on your album, EP, etc.
Here's an example of what mastering can and can't do:
Let's say a kick drum sounds weak. A mastering engineer may try boosting the low-end with a specialized mastering EQ to add impact, but if the instruments are poorly separated in the mix, the bass line will also be boosted by this EQ–in a way that causes the mix to become muddy.
Both mixing and mastering are essential. Understanding both the power and limitations of each process is crucial to your success and your art.
If you think your recordings need something in between, you may want to look into our stem mixing service.
*NOTE: Sometimes, a critical mix issue can be solved in mastering using 'mid-side' technology, which allows us to apply certain effects separately to the center of a mix and the sides. The reason is because some instruments are traditionally panned dead center (kick, snare, bass, vocals) and others panned to the sides (rhythm guitar, synth, cymbals, harmony vocals). For example, if a hard-panned synth is muddy it can be EQ'd without affecting the kick drum or vocals. It is still better, however, to fix these issues during the mixing stage.