The sensitivity control is just that. The higher you set it, the deeper you will hear a smaller target. As I understand it, the detector always throws out the same field, but as just said, by increasing or decreasing the sensitivity, you will effect the depth at which you will hear certain items. Take a coin and set it at 2 bars. While you will get good depth at the middle of the coil, you will notice a sharp loss of depth as you move away from the middle of the coil, compared to it being at a higher setting.
If the ground is mineralised or has a lot of tiny trash in it, then if you have the sensitivity set to high, you will start to get a lot of false signals (non repeating random signals). Apart from the fact that you will find it both distracting and frustrating, you can easily miss good targets. The best way to figure it out is to experiment with the setting. turn it up a notch at a time and use it for a bit, till you get to a point where it seems to get chattery. Back it of a notch or so, till the false signals settle down. At this point, you have your optimum setting.
The other reason you may want to back off the sensitivity, is when you hunt around metal poles. set at around 3 bars, will allow you to hunt closer to them than if you were set on 6 bars.
Good luck with the Ace.It's a first class detector and can tell you a lot about a target, once you master it.
Mick Evans.