I mostly agree with Z on the Id #. Dimes will be usually 70 or 72 (with a clear bell), nickles I say like 28-32, they have a definate knock sound of their own. Higher thirties gets into things like pull tabs. Quarters usually 80-83, often very attention getting. Silver jewelry can come in like a dime around 70, but bounce into the high 80's- they are very sharp and really demand attention, after a couple of these finds you will see what I mean. Pennies, I have not made up my mind on, they seem to be almost anywhere above 60 depending on their depth, and can sometimes frustrate me. When I tire of them I go to 3 tone- most will ring in the middle range, as opposed to the quarter, and dimes in the upper higher tone- although sometimes a penny slips in as a high tone.
As Z notes the 70 takes some getting used to. I have been trying lower disc settings like 20, which does seem to increase the depth. I usually keep my thresh at -3, sens - as high as can be, while stable. Early on I used a high disc, and it does keep from digging as many tabs, bottle caps, foil, and also Iron.
I have heard high disc, can lead to less depth- I am trying this week experiaments to see if this is true when I'm out there. Im learning to dig the really clear and not iffy signals. I usually bring a sample of each coin, and after i ground grab, toss them down to hear their sounds before starting. I know this does not account for deeper coin targets, but deeper ones I feel dont loose much of their sound quality as opposed to decibles. I like that it is feather light and really can be tailored for different settings and environments. Hope this helps, Curt O