The AT Pro with the 5"X8" DD coil is a painfully sensitive metal detector when searching a large area with lots of demolition debris and other tiny bits steel or iron.
I call it "rolling" sound rather than "proportional" because it give a clear view of not only the depth of what your coil is passing over, it also gives a fairly good idea of what the material is and how it's arranged.
For instance, I have one park with a pond that is frequented by ducks and Canada geese....and I mean in the hundreds.
Whether it be at night, or during the work day when nobody is around, someone peppers the pond with steel buckshot and the entire slope leading down to the water is saturated with these tiny steel balls.
There are also a lot of picnic tables and this appears to be a favorite hang out for wineos since there is a over abundance of aluminum wine bottle caps and the little rings left after the bottle is uncapped.
And, Corona beer must be consumed in this park by the gallon because every other good 85/86 signal, which should be a quarter is a darn Corona beer bottle cap.
But there are always a bunch of quarters to be found in this park and I've found a couple of nice .925 rings and ear rings...thanks to iron audio.
It's all in the listening because you can sort the short, tiny iron grunts out from the high mid-range silver as it passes over the quarters buried among the hundreds of steel shot.
When in Pro-Zero, with discrimination about 32, the rolling sound will give a tiny iron grunt, a good silver tone and then another barely discernable iron grunt. That's a Corona cap and a little wiggling will force a usually repeatable 62 from the false 85/86 signal originally heard from the aluminum bottle cap.
Otherwise I use iron audio to help define the size of a target when I'm looking for relics. The iron tone will start at the edge and stop at the other as the coil is moved over the target. And, changing positions around the target and waving it from different positions will help determine whether you're over a three foot section of old barbwire or a large piece of scrap from a old steel drum.
GL and HH.
AT Pro/GPP/Fiscars Diggers/BH Outback/CT Hand held