LandOLincoln said:
It may hit in the same notch but if you don't have iron discriminated and there is a large nail or other iron piece next to the good signal you may not hear the good signal. You may see the good signal on the screen but the audio could be nulled by the larger iron target. I for one do not look at the screen hardly ever. I go by tones most of the time and I always have iron disc on because I don't want to hear every nail i run my coil over.
Say you are in a really trashy area with tons of foil and nails and you run in all metal mode. You will have so many signals coming across your machine that most of the signals wont even put out an audio tone because of all the other trash. If you disc out iron you will HEAR foil and up. If you disc out iron and foil you will HEAR anything above that and so on. The disc modes are there for your benefit. You can choose to use them or not depending on your detecting style its up to you.
I thought that notching out iron just silenced the beep. The machine still read the iron signal but muted it's tone , consequently still masking a potential good signal.
Also, I thought running all metal mode gives you slightly more depth.