CD mastering is the process of "Making the CD sound good wherever
it is played".
We run every song through a series of filters to boost frequencies
where needed, and cut frequencies that are overbearing.
Then we run the whole thing through a Normalization process. This
sets the volume level for each song to a predetermined maximum.
Such as -.05 decibels from digital zero. This provides an even volume
across the length of the CD.
Then we put it on a test CD and play it everywhere. In places like
living rooms, kitchens, bedrooms, cars, large halls, and even in
stores where we can.