Here's something else interesting I noted, Dew, FWIW. Last night, I was hunting one site, and my noise cancel channel was 6. I was digging nickels at my usual "10-06" number. I moved down the street about a mile, to a place I hunt all the time. I have dug many nickels at this spot in recent weeks, at that same 10-06 value.
I noise cancelled when I arrived to this spot, and checked what number my machine chose. It happened to be "11." Fine. So, I hunted quite awhile and didn't dig any nickels, but did dig alot of pull tabs at 10-06, more of them than usual at that ID value. Kind of strange. So, a bit later, I got a penny hit, and dug it...and when I replaced the plug and re-scanned the area, I got a solid 11-05 signal a couple of inches away. Figuring it was a pull tab (as 11-05 usually is), but since it sounded good, and knowing that I dig an occasional, odd nickel at 11-05, I thought just MAYBE this nickel was part of a "pocket spill" with the penny. So, I dug it -- and lo and behold it was a NICKEL. So, thinking back to what I discovered earlier with my gold ring testing (low conductors seemingly hitting with a lower conductive value at noise cancel "11" than they do at lower levels), I wondered if maybe that's what was going on. So, I took a few nickels out of my pouch that I found earlier in the evening at the other site -- which rang in at 10-06 or 11-06 when I dug them. I tossed them on the ground, and sure enough, EVERY ONE OF THEM rang at a solid 11-05! So, I dug 11-05 hits the rest of the hunt, and -- while I dug more tabs than usual, I also dug a few more nickels!
This, and the earlier testing, leaves me with NO DOUBT that different noise cancel channels will have an effect on the CO number of at least the low-conductive targets; I'll need to do some testing to see if it has any effect on high conductors...but I'm thinking it might (as there are several days when pennies seem to hit just a bit higher, more like a silver dime...and I've never known why. Hmm....)
Steve