Threshold, Sensitivity and Ground Balance all work hand-in-hand. Even the proper Noise Cancel channel, to a certain degree. By that I mean setting any of them improperly can result in lack of performance. In fact, if you set your ground balance a bit on the positive side, you can hear the Threshold get louder as you lower the coil to the ground. If your detector is noisy when you sweep the coil, you could stabilize your detector by lowering the Sensitivity or lowering the Threshold. But if it is being unstable due to an incorrect GB, or an improper Noise Cancel Channel, lowering the Sensitivity or Threshold doesn't do anything but keep you from hearing the chatter. It still isn't operating at peak performance. And, by compensating for one incorrect setting by making another, you are actually making matters worse.
The Threshold should be just at the brink of making a steady noise. Loud enough to have it providing a steady buzz in the background. But not loud enough to really notice. To do this properly, set the Noise Cancel Channel first. Then check to make sure your Volume setting is at max. If you want it lower, use the volume controls on your headphones. (Tom might disagree with me on that one
) After you've set the NC and Vol, turn the Threshold to a point that you can clearly hear it. Then lower it until it disappears. Now, raise it back one number. It might not be a steady tone. But your objective is to get it on the brink of being such. I suppose you could say "on the threshold" of making a solid sound.
The purpose of the Threshold is two-fold. It serves as a background sound so you can hear a rejected target "blank out" the sound. And it serves as a background sound so you can hear it when it is over-ridden (replaced) by a target tone. Note that the Threshold tone pitch is not adjustable. And, it is a different pitch than any target tone. So, when it is replaced by either silence or another tone, you know the coil has passed over something.
The easiest way for me to explain why it is important to have a properly set Threshold is to do so by using values. It is tough to explain. And it isn't scientific by any means. But play along with me for a few minutes. Let's say that a dime buried at 5 inches will produce a target response with a value of 6. And lets say a quarter at 4 inches produces a target response with a value of 13. It would make sense that the dime produces a smaller value than the quarter, as the dime is a smaller target and is buried deeper than the quarter. For the sake of discussion, let's say you've set your Threshold at 5. We set it at 5 because that is the lowest number we can set it, and still hear it. (remember, this "5" is just an example, your hearing might require it to be higher or lower) It stands to reason that any target that produces a tone has to produce enough tone to overcome the Threshold, or you won't hear the change. So, if that dime at 5 inches produces a tone with a value of 6, it will provide enough tone for you to hear it over the 5, represented by the Threshold setting. Mathmatically speaking, it produces a tone that over-rides the Threshold by a value of one.
However, if you had set the Threshold too high to begin with, say a 9 or 10, that dime producing a tone with a value of 6 will fall 3 or 4 "values" short of over-riding the Threshold. As such, you won't hear that dime at 5 inches. You will hear the quarter with the Threshold set at 5 or at 10. But only because it is large and shallow enough to produce a tone with a value of 13, and over-ride the Threshold levels you set. Had the Threshold been set at a value higher than the 13 produced by the quarter, you wouldn't have heard it either.
Similarly you can set the Threshold too low. Using the same dime value of 6 and quarter value of 13, lets do the same test with a Threshold set at -2. Now, keep in mind that the actual Threshold level we could hear clearly was a 5. We sweep over the dime at five inches and it produces a target audio value of 6. We add this 6 to the -2 where the Threshold is set, and we have a +4. We wouldn't hear the dime because it did not produce enough "sound value" to get the tone loud enough to hear. Remember, we needed a value of 5. We ended up with a 4, due to the low "starting point". The quarter will produce a 13, as described earlier, and even though the Threshold is set at -2, will produce a tone loud enough to hear. We know we needed a value of 5 to hear a tone, we set the Threshold at -2, the quarter produces a tone with a value of 13, making the end result an 11. A full "6 points" more than we had to have, to hear it.
Now, with all this blah, blah, blah..
.... we should recognize that a proper Threshold setting is important. Setting it too high could result in targets not producing enough sound to over come the Theshold. And setting it too low could result in targets not producing enough sound to even get to the Threshold. In either case, you'll miss small and deep targets with an improperly set Threshold. JMHO HH Randy
