From my experience if I hear something like a CRT hissing or some electrical interference that is very high pitched, my ears start to ring when I am away from that sound. I'd suppose anything >= 8khz is what you want to bring down for those harsh high pitched sounds that end up making your ears ring. Probably gonna be told Im wrong. I dont do this myself because I dont have a lot of songs with stuff that makes my ears ring, but if I were to do anything just in case it would be removing high treble range for me personally.