I sometimes use the threshold in the Park, Field and Beach modes IF I am tired of listening to iron responses. In Park, Field and Beach modes the threshold tone is a reference tone which means it will give you a steady tone in the background that will go silent over any target that responds with a target ID that has been rejected in your search pattern. If you are hunting with nothing rejected in your search pattern in Park, Field or Beach mode the threshold tone will not do you any good. It will not amplify weak signals in those modes and it will not go silent over any targets if none are rejected.
There have been many VLF detectors that had a threshold tone for search modes that are discrimination modes. Some were just for going silent over rejected targets and some actually gave a boosted volume level to the target tones on weaker signals even if you kept the threshold tone on a low setting.
The threshold tone for the Gold modes has a little of both of the features described above. Most gold prospectors will hunt with nothing or as little as possible rejected if their detector will let them even do that. The Equinox Gold modes will let you reject and accept target IDs just the same as in Park, Field and Beach. The only ones I sometimes reject are -9 and maybe -8 if hot rocks and ground noise are just too much for me to audibly handle. If a target falls on -8 or -9 in that case, the threshold tone will go silent momentarily just like it does in Park, Field and Beach modes. On really weak targets that may be very small or very deep and aren't being rejected by discrimination, the Gold mode threshold setting will amplify the target tone even if the threshold tone is set at 3 or 4 which means it is basically inaudible. You won't hear the constant threshold hum but your weak targets will be easier to hear. Usually, since I only reject -9 most of the time, I keep my threshold tone in the Gold modes on 7 or 8 so I can just barely hear it. It really helps to hear tiny gold pickers and small gold nuggets that may be mostly masked by the iron mineralization and volcanic hot rocks. These small pieces of gold will respond with positive numbers on or near the surface but will have negative number responses just like iron when they are deeper due to the mineralization pulling their conductivity down. Even a fairly low setting for the threshold will help these target signals a lot.
So, to sum it up, the Equinox constant threshold tone will go silent over rejected targets in all of the search modes. It will also boost the target tone in the Gold modes if the target is really small and/or fairly deep. It has little effect on larger targets.
If I was hunting in an area like you hunt in for really deep silver or relics, I might try using the Gold modes with -9 and -8 rejected with the threshold on 8 or so. Any really deep targets with faint whisper signals that give a gold/lead/brass range VDIs or high VDIs in the upper 20s to upper 30s would be worth investigating. If those numbers stay constant in all swing directions I would be digging. I would try this in an area that has already been hunted for the shallower easy stuff or in an area that seems like it might have some really deep targets.
