Somebody that is an experienced user of the 4500------Can you tell me if there is any discrimination with this machine with relics. If so, is it only with hearing or is there a setting that causes this machine to null (if it really does) over ferrous materials? I have heard a little about the timing, but not a whole lot to really understand. I had a TDI earlier which seemed to have no discrimination at all. How does the 4500 compare? Information on anything is always appreciated. Thanks.........