Would 5khz get the best depth for copper and brass as well as silver? Or is 14khz the way to go? From what I understand 20khz is the best for trashy sites. I'm going to a site that iv found some great artifacts and coins at but now it seems if anything is left it's going to be deep. This will be my first time using the Anfibio. I watched alot of videos and read every page of the manual but practice makes perfect. Any help would be appreciated.