The Threshold, is exactly what the name implies, and that is the "breakpoint" where the detectors audio response will lie. That's kind of a simplistic explanation, but it will have to suffice for demonstration purposes. Set your threshold too high, and you will mask small and very low conductive targets. They wont be able to produce a response strong enough to overcome the already too high audio, and you wont hear them.(this is mostly in all metal, where you can hear the constant threshold hum in the background) You'll also enhance the audio response of every piece of junk in the ground, and make the machine very noisy. Set the threshold too low, and you will lose depth and sensitivity. Do this test.....Set your threshold correctly (IE: just audible), and then air test a nickel. Note the depth it gets. Now turn your threshold down a quarter of a turn below your hearing range. Do your air test again. Lost a few inches didn't you? The detector is probably still picking up the target, but YOU CANT HEAR IT at the same depths!!! The threshold isnt only critical in All metal, its critical in Disc as well. The "proper" way to set your threshold is to a level that YOU can barely hear. Too loud and its annoying and counter productive. Too low and its counter productive as well. Think of it as the way to adjust YOUR detector to YOUR hearing. Hope this helps you a bit....

Streak!