when you're swinging the coil, listen for any high pitch sounds, no matter how soft. if you can get the signal to repeat even 50% of the time, i would dig it. some deep coin signals are just little peeps, but the explorer is so good at tone ID that if it gives off a high pitch it's worth checking out. i have dug deep coins that only repeated from one angle, then when i check it at a 90 degree angle it doesn't make a sound. this may be due to trash near the coin. trust the tones the machine gives you. DO NOT only dig loud, totally repeatable signals. you'll be missing a lot of goodies. once you get a quiet, or short, high pitch signal pay attention to the depth meter and where the cursor is hitting. deep coins will not always ID as a coin in the upper right corner (but most times the machine is pretty darn accurate, even on the super deepies). i dug a wheat at 11 inches one time, and it was the softest repeatable high tone ever, and it was ID'ing accurately in the upper right. i have also dug deep silver and wheats that sounded good, but ID'd towards iron. trust the tones!
i swear by these settings: conductive mode. gain at 7. smartscreen. deep ON (although i started out with deep AND fast OFF and had great success). variability 10. MANUAL sensitivity (i DO NOT recommend auto sensitivity...yuck!). sensitivity 20-28 or whatever is stable in your area.
hope this helps. all of my success comes from hunting with a fellow named Dan (captain SE) that found just under 700 silver coins last year with the SE. he and i hunted together at least once a week and we would let each other listen to each other's signals. we'd do a lot of comparisons and he would talk about why or why not he thought the signal was a silver or not. i suggest hooking up with someone who is successful with the explorer and have him mark deep signals for you to listen to. there is no better way to learn what they sound like!
HH, Mike