Hi Rudy
Thanks for a great explanation of what threshhold is/does ! I have a question then. I just got an Xterra 705. I have the threshhold set in my headphones to a level where I can just barely hear it. It's basically a faint background humming noise.
Where I am confused is this; I have been running the 705 since I got it in All Metal mode with 2 tones. Low tones I ignore, high tones I dig. You said; "You see, when you go over a ferrous item, the threshold sound will usually null (will go quiet) momentarily." and "When you hear the threshold null out, you know you went over a ferrous item and you need to slow down and or change your sweep direction lest you miss a valuable target buried nearby the ferrous item. With a silent search machine you won't know it's happening."
When I go over a piece of junk, I get a low beep usually with a negative #. When I go over a good target I get a high beep with a positive #. I don't ever notice the threshhold null out. Is that because I have it turned down too low or because I am in All metal mode ?
Bill