my krks have two knobs one is called hf level adjustment and the other is the volume. what does the hf adjustment do ? and how do i know what to set it on ? ( it goes from -2 db to +1db ) and my volume goes from -30 db to +6db what is a good level to put this on ? when people say never put your volume all the way up are they talking about your computers volume or the speakers volume?