Equalization
The equalization of the mastering process lets the engineer precisely adjust how much low, mid, to high range frequencies should be heard, cut, or boosted.
It all depends on the the music genre and the way it was mixed prior to mastering.
Equalizers come in many forms from a 1 band, 4 band, even 6 band or beyond. There are the crucial 7 bands of eq that are very important to getting the sound to be warm and real. EQ can be the success or failure of a song if not done properly an you end up causing someone to not even want to listen to a song because it was just equalized poorly.
The beauty of the equalization process is that it can be adjusted after the fact of a mix that just has not been given enough of any type of EQ. This is why there is a need for the mastering process because usually when recording in the studio, the artist an engineer are not concerned at the moment with how the sound stands up next to a competitive music industry market. At least as far as the loudness is concerned.
