What is Automation? Automation is basically adjusting volume, EQ parameters or effect parameters to achieve a multitude of goals.
These goals can be used to add a little more mid-range punch to a vocal at certain areas (listen to Nickleback, you'll hear this one everywhere) which allows the vocal to “pop” a little more.
You also may use automation to add more reverb decay at a specific point in the song for creative purposes or you may decide to add just a little more feedback on the delay at a particular solo or vocal part.
Automation can also be used as manual compression which is what we will focus on. Manually going in and tamper peaks for a more natural, smoother response from the particular instrument that is being automated. The most common use for automation though happens to be vocal tracks. I do not care if you're Lara Fabian, Fergie or Sebastian Bach, chances are you get some automation, almost every vocal gets it.
Of course a vocal can be tamed with 6dB reduction on a compressor and the explosive peaks reduced with a limiter but this method takes away from dynamics; for instance you have a lyric that says something like:
“Today is the day I fight BACK! ”
Using the method described above, this can take away excitation from the word “BACK!” and does not help give it that push needed to really emphasize the word, so in place of heavy compression we would use automation to completely control the response of that word by manually reducing and boosting audio in specific points.
The initial plosive from the “Buh” in back would most likely get a .5-2dB reduction to reduce the plosive content yet allow it to come through in a smoother manner. The rest of the word would then be adjusted to be even in volume.
The second goal of vocal automation is to make sure that every single word, syllable and phrase is heard clearly. The vocalist is the star, they're the face of the group, so they should be heard quite well. That thought process is not one everyone agreements on though.
Most rap artists like to have the beat slightly above and around them (as if they're surrounded) rock / country artists typically want their voices to be heard either slightly above the music or a nice, even blend. If you want your vocals buried in a mix you should not be a vocalist or rapper though. Burying vocals does not sound good, the beat can still be focused on while you are clearly heard. You do not hear Snoop or Dre burying their vocals do you? Did not think so.
In essence, you can do a LOT with just one word. With automation you could reduce the initial impact of “B” and boost the “A” in back to sound like bAck! or emphasize the “ck” for a percussive timbre to the word.
I could get very in-depth on this subject but I do not feel that is necessary.