How can I make my captures louder?

When I make captures all of my levels appear to be right, but my captures seem
very low in volume, I usually have to boost them about 12db for my presets
to sound balanced.
Some captures I downloaded are at 0db and are very loud, others I boost 12db and they are not loud enough.
Usually the dirty captures are loud and the clean captures are low in volume.
Is there a way I can make my clean captures louder?