tank, whatever gold object example you are waving in front of your machine (that gives you a "solid bar everytime"), is just one sample target. So too can a given similar size small aluminum fragment (foil wad, wadded beaver tail, etc...) be made to bounce exactly at that "solid bar everytime" too.
You can get a variety of various types of gold items (rings of different sizes, bracelets, necklaces, earings, etc....) and you will get a different TID, and different repeatility, bounce, solid-ness, etc.. on each one. They'll all hit a bit differently. I also guarantee you that once you memorize the various types of hits that various gold jewelry items can bounce/sound at, that I can take aluminum can shards, foil wads, bent up beaver tabs, etc.... and get them to give the exact same sounds/bounces too :P
So no, there is no way to use your graph, tones, etc... to indicate gold verses non-gold. All you can do is tell low vs high conductors. And unfortunately, as I've said, gold and aluminum share the same TID. That's why to increase your gold jewelry finds, you should concentrate on WHERE you're hunting, and not so much the machine. Just keep your disc. down low to *only* reject iron. Make sure you can still pick up tiny (little finger nail sized) pieces of foil, in sample air tests, so that you know you can pick up little dainty rings, earings, charms, etc...
If you find that wherever you're hunting (parks as you say) that you're going crazy digging aluminum, then you either need to 1) re-think your hunt spot, and choose a swimming beach or sand-volley-ball pit, or other such better ring-ratio spot, or 2) you need to cherry pick on your disc. setting, and tune out some of more commonly recurring junk low conductor items. Be aware though, that the minute you do this, you stand a chance of missing something gold that just happened to mimic that commonly recurring junk item
