Song mastering is different than more involved CD or vinyl mastering for a number of reasons. First, it exclusively refers to mastering your individual songs themselves so you don’t have to worry about sequencing. Sequencing refers to the ordering of tracks on a CD and the care in terms of spacing them out, creating a table of contents, etc.
You don’t have to worry about these kinds of things when you don’t have an album file which is going to be replicated, so song mastering is much less involved and exclusively targets the audio itself. That’s the difference, betcause you’re looking to release you music exclusively for online audiences in digital format.
But what specifically happens in song mastering? This is the part of audio post production where certain effects digital or analog are applied to your final rendered mix in order to attain the best possible sound from that audio. Song mastering can be used to significantly improve the audio quality itself even if the recording conditions were lacking. The mastering process can be used to compensate what you didn’t have in the tracking stage. How does this work?
Say you didn’t mic the guitar correctly and it didn’t pick up enough of the instrument’s natural bass tone. By applied equalization and boosting the presence of the low end in that audio spectrum you can thicken out a track which is lacking in the lower end of the spectrum at those lower frequencies.
Boosting the other end of the equalization spectrum will yield a different result as you can make the higher end more prominent in the mix to give the effect of removing the wrapping paper from around the mix so that it comes through much more clearly. The audio will be much crisper but you need to use these effects artfully and sparingly as if you don’t and go overboard then your audio will come off as sounding tinny and grating. Certain frequencies will annoy your listener and the sibilance will be much more perceptible at the cost of that mix’s quality.
You can give the impression of realistic room ambiance by applying reverb after the fact, as well. This can be used to correct a flat mix to give it a lift out of the headphones three dimensional feel to it with a great deal more life. You can think of song mastering as being like a painter crafting a beautiful work of art out of a blank canvas and a good mastering job will substantially boost the quality of your music and provide a much more professional product to your listeners.