Comp button on stereo?

I have a stock stereo in the car. I just noticed there is a "comp" button. What does it do?

Do you have an owner's manual? :)

Compression
Press “COMP’ to make loud and soft
passages more nearly equal in volume.

Nope, Dont have a manual. Bought the car used and it didnt come with one. So comp just makes the volume louder a bit?

It makes all the difference sound frequencies almost equal in volume.

http://shbox.com/pdf/manuals.html :)