Originally Posted by 10ndayii
Now since I now know that am wondering if in upward compression the attack , release e.t.c alters the soft sounds rather the loud sounds that's my question . "
Attack and release always "alter" whatever is happening above the threshold. It can either be just the transient peaks, or the softer "body" parts of the sound, depending on where you set your threshold and attack/release controls. Since the peaks always get above the threshold first, you'll have to use a longer attack time to be able to have them more or less unaltered, then you can tailor the sustain of the attacked (compressed) parts with the release.
Check out this great article on comparing upward and downward compression and their curves, among other things: http://varietyofsound.wordpress.com/...-and-expander/