Threshold ?

I have dealt with machines with a threashold , and also those without a threshold ....I have seen many times where insructions show HOW to set the threshold , but none of these instructions DESCRIBE the threshold .....I have questions about said "Threshold " .......

1 ) What is the ACTUAL description of Threshold on a metal detector ? ....

2) Does the threshold effect depth , or is it mearly an audio feature ?

3) Does the threshold effect sepration of targets ? or again is it an audio feature ?

4) Other than the ability to hear when I am coming up on , or moving away from a target , what effect other than audio will I incur by turning the threshold down ?

The reason I ask this is because when hunting with my Excal on Black Sand Saltwater beaches and I get in or near the water , I also deal with many trashy targets along the way ....So I am basically listenning to a barrage of noise and targets in my ear that I am trying to weed thru to hear a good target .... By turning the Threshold down to just not hearing it ( just under audible ) I can somewhat tame the noise and have an easier time of hunting .....I am wondering if I am loosing out on depth, seperation, or what exactly other than audio do I miss out on by turning my Threshold down to eliminate unwanted noise ? ......I still have my volume turned up , and I can still hear good targets loud and clear when I hit them , but wonder if I'm missing anything by hunting this way ......Thanks, Jim

synthnut --

This is a SUPERB question. Really is. I wonder the same thing, and with "sensitivity" too.

I'll try to paraphrase what Mr. D. has said based on my understanding, at least W.R.T. F70/75/T2 machines: first, there is NO adjustment to "transmit power" available to the user. It is fixed, period. Sensitivity affects how 'small' or 'weak' of a target the "receive mechanisms" of the machine can "see." Then, threshold is like "squelch," where you are adjusting how "strong" the received signal needs to be before it can break the "squelch" and thus be reported by the machine to the user.

My interpetation of that was that the Sensitivity determines how small of an "electromagnetic field disruption" (i.e. how small or deep of a target) will be sensed by the receive coil, and then understood to be a target by the machine processors/software. The higher the sensitivity, the "weaker" the target which the machine can decipher. Then, threshold affects whether or not the signal (assuming it was received by the machine in the first place, as determined by the sensitivity), will be reported to the user. In other words, even on max sensitivity, some targets will obviously be too "small" or deep to be "seen" by the detector, period. In that case, threshold will do nothing to help this situation. But, for a very weak signal which high sensitivity settings WILL allow the machine to "see," then whether it will be REPORTED or not to the user, as a tone or whatever, is determined by "threshold."

Again, this was for F70/75/T2 - type machines. It may be different on others; also, this is just my (imperfect) understanding of what I have read Mr. D. to say in response to similar questions before. I hope that additional, more thorough explanations will follow, on this thread, as I really want to have a more in-depth understanding.

Thanks for asking this question -- it's a very good one, IMO.

Steve

Steve
Thanks for the explanation ....... I'm sure that this is a true for a LOT of detectors , not just Fishers ...... If the Threshold is nothing more than an audio adjustment to apply or reduce the gain from an already reported ( from the sensitivity ) target, in the form of audio , than I have nothing to worrry about by turning it down other than perhaps missing faint targets which I am not all that concerned about anyway as I will not have the chance to dig that deeply in the water anyway .......Thanks again for your answer ...It's appreciated ....Jim

Makes you wonder why it takes like 7 clicks before you start hearing the threshold. There has to be a point like was said that there is no benefit or where it might be more beneficial NOT to have a threshold, like on a beach. Personally i like and feel i need that threshold while say field hunting. I like to know when im in and out of a target zone... the field is a big place.

Dew

Bad dirt (or wet salt) will cause a continuous 'threshold' ......on threshold-based detectors. This is why there are EXTRA detents (adjustments) to go quite a bit below......what we would (otherwise) consider a '0'. Different dirt will cause different threshold levels.

Yes, threshold is directly related to depth performance. If you have threshold adjusted so that you JUST BARELY hear a threshold......and you pass the coil over a 'fringe' target..............................now drop your threshold to be slightly silent.....or even lower.......and see what happens to that 'fringe-of-detection' target. You will lose it.

Ideally.......you want to 'just barely' hear a threshold; yet, there are some folks that 'fatigue-out' at a quicker rate....by virtue of hearing a continuous threshold hum. In this case; find where you 'just barely' hear a threshold hum........then.......adjust the threshold hum to JUST BARELY inaudible. And.......I must admit......sometimes the human brain 'triggers' better on "no-audio.......then target-audio.....then no-audio" again. It is more differentiable/intelligible.......but......at a cost of a slight reduction in overall depth/performance.

Thanks Tom ...I appreciate the explaination ..... I know when talking to OleBeechNut , he has a method of running in P.P. mode (all MetaL ) on the Excal and he has Docs audio amp wired in ....He goes back and forth lowering the Threshold, and then pumping up the volume on Doc's amp, then lowering the threshold again, and increasing Doc's amp , until there is a low threshold tone, but when a shallow target is reached , it is LOUD !!!......DEEP targets are nothing more than a change in Threshold ....... THIS is his way of getting the extremely deep targets, by listening to the threshold change .......I could NEVER do that where I am since it's WAY TOO NOISY !!!..... Between the Iron , the Salt , and the Trash, I don't stand a chance at trying OBN's method ......I would have to go to NJ where they are sanded in to use that method of hunting ......

As I stated earlier , I don't mind missing the really deep targets as I will be in the water .and won't have a chance to dig THAT deep anyway with the water running back and forth with the currents and the hole constantly filling up with sand ..... Hopefully out a little bit deeper I won't have to deal with as much trsah and will be able to turn the threshold up a bit higher ......THanks for the info .....I appreciate it .....Jim

BTW ...The reason I am asking these questions is that EZ and I went to 2 beaches in the area .....One beach I went into the water and had no trouble G.B. my AT Pro to right around 14 in the Saltwater .........When we hit the next beach , there was NO WAY I could come anywhere near a good G.B. in the Saltwater ...... THIS is the beach that has so much trash, iron, and Salt ...... The one machine out of the 2 that can handle this beach is the Excal !!...... The AT Pro just runs pretty WILD on this beach ..... You can calm it down to a a degree , but by the time you drop the sensitivity down to where it runs 1/2 way decent , it's not worth using it .....



Edited 1 time(s). Last edit at 02/19/2011 08:01PM by synthnut.

The last paragraph is very interesting in regards to why the AT Pro 'flunked' on the second beach and the Excal didn't. Anyone want to venture an opinion why?

As Tom mentioned many times , Multi Frequency machines handle Salty Black Sand beaches better than Single Frequency machines !!......Like the old saying goes " he said tt , I believe it , and that settles it " ....... I say this because I have witnessed it !!....I have experienced it !!......and I am also convinced that when going on beaches that are the worst of fhe worst , that the CZ-21 runs as smooth as a babies butt !!..... Again , I have experienced this !!..... The Excal is not far behind in this scenario , but the CZ is AMAZING .... On other beaches they run neck and neck and no big difference either way ......Go up on the dry sand , and the AT Pro turns into an ANIMAL !!!...... It SLAMS coins that are 6-8 inches down and makes them sound like they are a couple of inches down ......It hits HARD and ID's so well ..... Hit a Quarter signal , and then hit the Iron Audio button ....If there's a grunt , keep walking .....If there is no grunt .....Dig your quarter !!..... When EZ would hit a target , I would run my coil over it and tell him EVERY time what coin he was going to dig .....SPOT ON, EVERY TIME !!....No more pennies !!....Jim

is this true, I was lead to believe it, when you run the thresh and you hear a null in it, it is telling you that it's a deep target

When you are running a threshold and it nulls (goes silent), it is an indication of a "rejected" target. If your threshold remains quiet for any length of time, you can be missing good targets due to a form of masking from the "rejected" target(s)/ VDI. A faster "Recovery Delay" setting can help mitigate this somewhat. Recovery Delay is the amount of time the detector needs to "reset" itself after detecting a specific VDI until it can resume detection of the next target VDI.

"Happy hunting" - Schultzie

schultizie is correct !!...Whatever you have discriminated on your machine , you will either hear either NO Sound from machines without a threshold , or you will hear a null from machines with a threshold when you pass over these targets that you have dicriminated out ...... What you are referring to as far as threshold and deep targets is ...........When you run a threshold machine in ALL METAL or whatever that company calls ALL METAL mode , you are accepting EVERYTHING ...You are not discriminating ANY targets .......When you are in an area that has been sanded in , or has VERY DEEP targets in the ground , and very few of them , sometimes they are so deep that you can't hear any tone , or beep , or get any number on your detector , as the detector passes over that target since it's so deep .....What you WILL hear if you listen closely is a change in the threshold on a threshold machine ......In other words , suppose you have your threshold set very low , and you hear a constant hum the entire time you are hunting ....It never changes if your coil does not pass over a target , and then all of a sudden it changes the slightest bit , and you check it in a few directions and you see that the threshold changes each time you pass this area ......This is not a NULL ...It's what is called a Change in the Threshold .......THIS is what is refered to when you are hitting DEEEP targets .....Hope this helps ....Jim

that's what I said, deep targets, I except -35 to +95 on my XLT, and dig anything that has a repeatable signal