With the Threshold set at Zero, you have completely disabled the Threshold sound and your detector will only produce a target tone on those target values you have set to be accepted. If you drop the Threshold down below zero, you have "turned the threshold back on" (compared to running at zero) but not to a point that you can hear it. As such, small targets may not produce enough of a target response to get your attention. Conversely, if you set it too high, small or deep targets may not produce enough target tone to overcome the audio sound of the Threshold. Although there has been a couple who have disagreed with that theory, I have proven to myself that Threshold levels do affect the ability to detect small, deep targets. Even when running minimal discrimination, I set my Threshold at an audio level that is just barely audible. That way I know what is under the coil at any one time. And I can monitor any "chatter" that may develop during the hunt, due to RFI, EMF or simply sweeping too quickly. My suggestion would be, if you want to run without an audible threshold, set it one level lower than what you can actually hear. That way it is still there, you just don't hear it.
With all that said, if you listen closely, you'll notice that the Threshold tone and any target tone are two entirely separate tones operating at two different pitches. On the older machines, (without notch discrimination or multiple tone capabilities) the threshold tone would gradually change to a target tone when you passed the coil over an accepted target. On rejected targets, the threshold tone would null out. On the X-TERRA, the threshold tone will still null out on rejected targets, if you have that threshold set loud enough to hear it in the first place. But that same threshold tone will not increase or transform on accepted targets. Instead, it is replaced by a target tone of a different pitch. Again, none of the target tones are the same pitch as the Threshold tone. With the settings you mentioned, keep in mind that running a Threshold at a negative level will not provide a null on those -8 targets you have rejected. It won't, however, provide nulling on what you can't hear to begin with. As such, your detector will not let you know when a rejected target might be blanking out an adjacent accepted target. JMHO HH Randy
