There is no need to notch out a complete range of targets.
Let's say pull tabs.
Dig one up, get your coil centered and note the TID with the coil centered.
Then apply a small amount of notch around that TID, you can easily go as close as 1 point.
When you're swinging along and approach another pull tab, TID will be lower and the pull tab will sound of clearly.
Center the target under the coil and the signal will start to break up.
Point is not to go over the pull tabs not knowing they're there, just to quickly confirm a possible pull tab.
Or target in your notch range.
I've dug damaged pull tabs, other design pull tabs, but also small jewelry nicely sounding of wright next to the pull tab range.
And now and again, when the signal breaks up just like a fully grown pull tab would, I just leave it there.
Same can be achieved by adjusting the tones to change at the TID of the pull tab.
You'll get a fluttery mix of tones indicating a target in pull tab range, apply a little notch and that pull tab range will receive a very unique sound.
Foil wrappers have the tendency to make TID jump in a small range, again with the notch you can have a few points in that range blanked out.
Let say 2 points disced with a little iron volume added, 2 points accepted, 2 points notched It will provided a very distinct signal for foil wrappers.
So I've got Iron, foil, low conductors, pull tab range and high conductors.each with a very different signal.
Works for me.