Dwayne --
It really depends on what you are hunting for, and what you don't mind "missing." You say that you have been hunting "new" fields, and have been digging small aluminum foil; from this information, my guess is that you are hunting both modern clad coins AND jewelry, and that you are digging any signal above your disc setting. This is what I deduce from your post -- is this correct?
A couple of things I can say...if you want to hit ALL possible jewelry, you gotta dig small junk -- including the small foil pieces! The bad news is it's a pain; the good news is that these machines are that sensitive! Over time, you will learn to "hear" the size of the target based on the machine's response to it -- both in disc. mode, and in pinpoint mode. Then, with the VDI as additional information, you can choose whether to dig that really small stuff or not -- as you will have an idea of the "size" and conductivity of the target before you dig it. Keep in mind, though -- if you decide to DIG, you'll most often end up with a tiny piece of junk, BUT at the same time you will also obviously increase your chances of finding small gold (earring backs, very small rings, thin chains/bracelets, etc.). If you decide NOT to dig, you obviously will dig less junk, but will also miss some small gold.
What I do, is, when I hunt a place that I think may hold small gold jewelry, I DO dig those small-sounding, 40s VDI-type targets (like, in sand boxes, wood-chip lots, volleyball courts, etc.), and I would also do so on the beach. In trashy parks, though, I ignore some of those 40s VDI targets, and concentrate on the bigger-sounding, slightly higher-VDI stuff.
If you just want to dig the larger gold, and all coins, you can choose to "not dig" anything below about 50. If you want coins only, you can choose not to dig anything below mid 50s. If you are willing to ignore nickels (which VDI mid to upper 50s), you can choose not to dig anything below low 70s (where the lowest VDI zinc pennies can hit). If you are willing to dig only coins that are modern, but NOT zinc pennies, you can choose to dig only targets that VDI above the upper 70s (where the lowest-reading copper cents will mainly hit). My point here is, you need to decide first what you are willing to "miss," and what you absolutely do NOT want to miss, and then go from there.
I'm sure you already know all of this, but hopefully there is something in there that is useful. Yes, turning down the gain can help some, too...but again, I feel that you first have to decide what you are willing to "miss," and then set your machine up accordingly. It's sort of a "cost/benefit" decision that each person has to make for themselves, on a given day, at a given site. For me, it changes based on circumstances.
Steve
