I have an equinox 800 on order and have read the manual twice. I am 63 and sometimes there is something that has be baffled and that is threshold. For some reason no matter how many times I read the manual I am confused. It almost sounds like if the threshold is set correctly there should be a slight continuous hum and when something is detected if that item is notched out the hum will go away and be quiet and if it is a good item it will generate the appropriate tone. Is this what it means? If not maybe someone would be kind enough to help this old geezer as what it means...thanks in advance.