I am anxious to hear what a Minelab rep has to say. Hopefully it is someone who has put in the time in the field. Marketing sometimes has a different perspective.
Regardless, while you are waiting for a response from Minelab, I'd suggest a couple tests you can do yourself, to better understand how to interpret the sounds of target masking. Set your E-TRAC up in the standard Coin Program, and the Iron Mask screen as open as you can get. Doing this will allow you to switch back and forth quickly, so you don't forget what it is you've heard in the previous mode. Gather up some coins and some ferrous targets of varying size. I used a quarter, a dime, a penny, a 6 inch bolt, a 16 penny rusty nail and a chunk of iron. Unhook the rods while keeping the cable connected and hold the disassembled detector securely. This way you can control the path of the targets being waved under the coil, as well as the control housing. After turning on the E-TRAC, make sure you can hear a clear and distinct Threshold. Afterall, the Theshold is what is being "nulled" by rejected targets. Set the E-TRAC to the open screen and sweep each target under the coil, making a note of the "width" of the audio response of each target at a given distance from the coil. Now, switch to the Coin mode and resweep each target again. Notice how the larger ferrous targets "blank out" the Threshold for a much larger "width" compared to the width of the signal they produced when you swept them in the open screen mode? The large chunk of iron I used blanked out the sound for a distance of at least 5 inches on either side past the edge of the coil. This is known as target blanking. Now, and you may need someone to help you hold the detector, hold two targets side by side (ferrous and non-ferrous) and sweep them under the coil again. By changing the sweep speed, direction of sweep, distance between the targets and the actual targets themselves, you will get an idea as to how important sweep speed, direction of sweep and spacing between targets is, when it comes to target separation. Do that in both the open screen mode as well as the discriminate mode. With all circumstances EXACTLY the same, and depending on how large each of the two targets are in comparison, you may be able to squeak out a signal from the non-ferrous target. But again, that will depend on the size of the non-ferrous target, the size of the ferrous target(s), the distance between each target and the speed and direction of your sweep. Not to mention how closely you are listening to the sounds. If the adjacent ferrous target is larger than the non-ferrous target, or the ferrous target is between the coil and the coin and is larger than the coin, you won't likely hear the coin. But you'll see that with these tests.
My opinion....In a typical hunt situation, hearing all the targets (open screen / modified Iron Mask) makes me slow down in attempt to sort out the trash. If I hear a bunch of sounds, I slow down. If I get tired of digging some particularly plentiful pieces of ferrous trash, I can raise the conductive level of the Iron Mask screen to black out their range, with the press of a button. (try that on your test materials) On the other hand, when hunting in Coin (discriminate) mode, the nulling effect from the multiple ferrous targets doesn't draw my attention. If it did, and I made a concerted effort to slow down and resweep the area from different directions, I would eventually pick out many of those targets that were initially missed due to target masking by the settings of the Coin Mode. But based on what I've learned in the manner I use my E-TRAC, I believe that nulling a rejected target "hides" more coins than if I were listening to sounds from each target. Partly due to my interpretation of test results I've encountered. And partly due to my not paying as much attention to nulling as I do tones. But again, this is just my opinion, based on the manner I like to hunt. You can make that determination by trying the tests yourself. HH Randy
