In conductive sounds with lots of iron around you can drive yourself crazy watching the screen to see if that high tone is a coin or iron. In ferrous sounds you can pretty much do it by ear and not look at the screen.
Lets say your machine is set up to play the musical note "C", two octaves below middle C for the lowest iron tones in ferrous. You're swinging your coil amongst all the nails hearing C, C, C, C, C, C, and all of a sudden you hear a "C#" or a "D". That's your que to check it out. Go back over that slightly higher toned target and see if you can make it go even higher. Sometimes if you change your sweep angle you can make it much higher and you know you want to dig it. If I'm at a site where lots of old goodies have been found I'll even dig the "C#" target or at least open the plug and stick my probe in. I hope you've got a Sunray X-1 probe because they save so much time while investigating targets.
Just to reitterate, in ferrous sounds the iron is always the same low tone and anything higher than that low tone is nonferrous. Could be just a little higher or it could be alot higher. And you can change how wide you want the musical range to be by changing your variability and limits settings.
And YES silver and copper coins can sound off quite low in ferrous sounds. You'll find that the cursor can sometimes be pretty far to the left side on the top of the screen and still be a copper or silver coin.
HH
Neal