Filter settings are VERY important on the DFX. For me, that was the "ah-ha!" moment for learning the DFX. Basically, you want the lowest filter that will give you smooth quiet operation at your normal sweep speed. Find a deep coin-sized target that is right at the deepest edge of the detection limit, then start trying the filters one-by-one, until you find the one that works the best for your soil. You'll see it obvious when you have the correct filter selected. You'll be like "wow, that is so much better" when you get the right filter selected. For me, it is usually 4 and sometimes 3. If you are getting only 4 inches, you may be waaay off. So once you get a good filter setting, you may have to go find another deeper target to further fine tune your filters on. Find the best filter first, then you can mess with the AC/DC sensitivity and preamp gain. And a Sweep Speed setting of 5 is a good all-purpose safe setting for good performance in most areas. I think the stock program is a little high, maybe a 10 if I remember correctly.
But get the right filter selected first and foremost. The DFX is a fine detector. It sometimes gets a bad rap from people that don't understand how to use its settings. But once you figure out how to use those additional settings, you'll never want to be without them.
