Most detectors are known as motion detectors. That means the coil must be in motion to detect targets. When you sweep the coil over a spot of ground with nothing metal under the coil, the signals change very slowly, or not at all. When you pass over a metal target, the signals change very quickly. The electronics in the detector that measures the rate of change is a differentiator, or high pass filter. One filter is used to measure the effects of the ground, keeping your detector in phase. A second filter is used for discrimination. These detectors (with two hardware filters) are known as "two-filter" models, like the earlier Whites Classics. Those who used them know that they worked well in low to moderately mineralized soil conditions. And, they provided a very fast response between adjacent targets. Detectors known as "four-filter" units, like my XLPro, ( as well as XLT and Quattro) actually have three high pass filters per channel. They also use what is referred to as a "feedback" design to increase the gain for fast changing signals. This "feedback" circuitry is sometimes referred to as the fourth filter. Regardless, the "four-filter" units are capable of doing more signal processing than the two -filter units. This improves their performance in ground with higher levels of mineralization (compared to the two filter units). And also provides more accurate discrimination and deeper levels of detection, compared to the two filter models.
I may be wrong, but I don't think the DFX has a choice of 2 - 6 filters. From what I understand, the first two filters are actual hardware filters. The third filter and the "feedback" filter are implemented via software. These are known as digital filters. This digital filter is what is being changed when you adjust the numbers from 2 - 6. By setting it at a 2, the digital filters are turned off, allowing the DFX to perform like a two filter Classic. When you set it at 3, the third high pass filter is implemented, but the "feedback" filter is not. When you set it at 4, both hardware filters and the two software filters are all implemented. This allows it to react to targets similar to the XLT. Setting it to 5 introduces even more "feedback" for an increase in gain. And setting it at 6 maxes out the "feedback", or gain. As you can see by this explanation, using a lower number will allow the detector to respond quickly between targets. It also provides a very forgiving sweep speed. Higher settings will provide better ground "neutralization", at the risk of some chatter due to the increase gain.
So to answer your question regarding filters on the X-TERRA.......recognizing that the X-TERRA transmit and receive signals are analog, we can assume it has two in the hardware. But with all the signal processing being done via the digital portion of VFLEX, the smart coil communicating with the microprocessor in the X-TERRA may eliminate the requirement for what we commonly refer to as filters. With all those 1's and 0's flying by, I don't know of any way to determine the number of filters on the X-TERRA.
Interesting question. Sorry I can't be more specific on the answer. HH Randy
