Any benefit to threshold in all metal no discrim?

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Zyrbalax
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Any benefit to threshold in all metal no discrim?

Post by Zyrbalax » Wed Mar 13, 2019 10:42 am

Hi all,

I am generally now detecting in all metal mode with no discrimination so I can "hear" everything.

I concluded when I switched to this mode that actually there was no point having a constant background hum if I'm not discriminating anything out - there's no "blanking" needed to tell me I've just gone over something that my machine has ignored, because it's not ignoring anything.

Is there any reason why having an audible threshold is useful under these circumstances? Other than the reassurance that the machine's still working of course...

(Occasionally I do notch out -10 if there's just too much grunting going on, in which case I do bring in a low threshold.)

Thanks all
Z


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Re: Any benefit to threshold in all metal no discrim?

Post by Bors » Wed Mar 13, 2019 11:03 am

Quite a few detectors now have S.A.T. (Self Adjusting Threshold) which offers a significant advantage when searching in and out of salt water or over mineralized ground.
S.A.T. helps keep the metal detector operating at maximum sensitivity without requiring constant adjustments by the operator. It improves the stability, reduces noise, and allows higher gain settings to be used.

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Re: Any benefit to threshold in all metal no discrim?

Post by Rayc » Wed Mar 13, 2019 11:11 am

The Sabisch book says '....most users will opt to reduce the Threshold value to 9 or 10. The Threshold value can be reduced slightly below that point so that the detector operates as a silent-search detector with no noticeable impact on sensitivity or detection depth.'
I use the Safari in All Metal simply because I think it has a faster response in that mode - but I leave a Threshold hum because I sometimes switch between modes when deciding whether to dig or not; it's one less adjustment to make.

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Re: Any benefit to threshold in all metal no discrim?

Post by Zyrbalax » Wed Mar 13, 2019 12:11 pm

Bors wrote:
Wed Mar 13, 2019 11:03 am
Quite a few detectors now have S.A.T. (Self Adjusting Threshold) which offers a significant advantage when searching in and out of salt water or over mineralized ground.
S.A.T. helps keep the metal detector operating at maximum sensitivity without requiring constant adjustments by the operator. It improves the stability, reduces noise, and allows higher gain settings to be used.
On the Safari I think that's called "Sensitivity", which at the moment I'm still leaving on Auto; from other posts I think the consensus is that you can get a bit more depth by manually adjusting the sensitivity; one more thing for me to learn in due course :)

The threshold I'm talking about is the background "hum" the machine makes, which is interrupted by target signal beeps or by blanking when running over something that's been specifically discriminated out.

Thanks Bors :)

Z
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Re: Any benefit to threshold in all metal no discrim?

Post by Zyrbalax » Wed Mar 13, 2019 12:13 pm

Rayc wrote:
Wed Mar 13, 2019 11:11 am
The Sabisch book says '....most users will opt to reduce the Threshold value to 9 or 10. The Threshold value can be reduced slightly below that point so that the detector operates as a silent-search detector with no noticeable impact on sensitivity or detection depth.'
I use the Safari in All Metal simply because I think it has a faster response in that mode - but I leave a Threshold hum because I sometimes switch between modes when deciding whether to dig or not; it's one less adjustment to make.
"Silent Search Detector" - yes that's what I'm doing :)

I don't often switch between modes at the moment, although again that's something I should practice - understanding the difference between ferrous and conductivity better would I'm sure help me cut down the trash :)

Thanks RayC :)

Z
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Re: Any benefit to threshold in all metal no discrim?

Post by Bors » Wed Mar 13, 2019 6:58 pm

Zyrbalax wrote:
Wed Mar 13, 2019 12:11 pm
Bors wrote:
Wed Mar 13, 2019 11:03 am
Quite a few detectors now have S.A.T. (Self Adjusting Threshold) which offers a significant advantage when searching in and out of salt water or over mineralized ground.
S.A.T. helps keep the metal detector operating at maximum sensitivity without requiring constant adjustments by the operator. It improves the stability, reduces noise, and allows higher gain settings to be used.
On the Safari I think that's called "Sensitivity", which at the moment I'm still leaving on Auto; from other posts I think the consensus is that you can get a bit more depth by manually adjusting the sensitivity; one more thing for me to learn in due course :)

The threshold I'm talking about is the background "hum" the machine makes, which is interrupted by target signal beeps or by blanking when running over something that's been specifically discriminated out.

Thanks Bors :)

Z
No , the Sensitivity's the THE Sensitivity,. If you leave it in "Auto " you WILL lose depth. The Detector will often over compensate in auto.

I know exactly which "thing" your referring to when you describe the "Threshold" .
Using All metal is a good way of getting optimum depth but comes at the trade off of doing exactly what its called You hear one tone for "all metals ", there is no different tones to help you judge the target and there`s no discrimination windows filtering the received signals, and its just RAW sound of whats below you . The threshold will make little to no difference as far as discrims concerned affecting the signal of the target ,as its NOT a discrimination . The threshold is just a continues back ground hum set accordingly to inform you ,you have hit a target and that gets electrically "altered /disturbed " when a metal target is received. But if you can ,get into the habit of not using Auto sensitivity or your depth capability is compromised by using Auto..
Last edited by Bors on Wed Mar 13, 2019 7:18 pm, edited 1 time in total.

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Re: Any benefit to threshold in all metal no discrim?

Post by Bors » Wed Mar 13, 2019 7:10 pm

OK this quite long post might help you understand the Threshold .Its one I picked up because Its quite informative plus to be truthful it saves my typing finger cramping up . But if you can bear with it its informative if nothing else..( + I`m pure lazy) :))

"Many newbies go out and buy a detector that has an adjustable, audible threshold and are confused by its function or proper use. The situation gets even more confusing if the detector also has a volume control. Oh wait, you also bought a nice set of earphones and they also have a volume control. What to do, what to do.

Ok, first, lets look at what is this so called threshold and what purpose an adjustable threshold serves. Then we can tackle what to do with the volume control. Setting both properly maximises your ability to get as much depth as you can from your detector.

Not all detectors sold now a days have an adjustable threshold that you can hear. These latter machines are termed "silent search" detectors. Basically, they are quiet running until you sweep over a target and then they beep at you.

You can think of the threshold as a type of squelch control as found on a CB or short wave radio. Without a squelch control circuit on a radio, the speaker would be putting out a constant stream of hizzing noise when you are not tuned in to a station. This can be annoying. By dialing up on the squelch control, we are basically telling the radio that we don't want to hear a signal until it reaches a certain strength. The hizzing noise coming from the speakers is suppressed because it is low energy background noise and the radio is quiet until you tune in an actual signal. By the way, on some detectors the manufacturer calls the knob that adjusts the threshold a "tuning" knob. Now you know why.

If you dial in even more squelch, you'll start to miss some of the weaker signals from far away stations.

This is exactly how the threshold control works in a metal detector!

With a silent search machine, the "squelch" control is factory set to suppress the small signals and allow signals with a strength above the threshold setting to get through and make a "beep". If you bought a detector with an adjustable threshold (good for you!), you want to set it such that you can barely hear the threshold sound on your earphones. The sound is hard to describe, but it sounds like bees buzzing your ears. By having the threshold at this setting, right on the edge, you are guaranteeing that very weak signals (like from deep targets) will be able to get through the threshold control. This gives a machine with adjustable threshold a slight depth edge over a silent search machine, everything else being equal. This is because a very weak signal may not get through the "squelch" setting of the silent search machine.

You don't want to make the threshold any louder than what you can barely hear. If the threshold hum gets too loud, you'll miss the real small signals again. This time because they are drowned by the louder threshold buzz.

If like some other folks you can't stand that constant low level buzzing sound of the threshold, you can always back it down a hair until it is not audible anymore. Essentially, you'll be running the detector as if it was a silent mode machine. But you pay a price for doing so. First, you'll lose some of that depth advantage you had over a silent search machine. If you back off on the threshold to just make it inaudible and no more, then you haven't lost much depth. Second, you'll lose some potentially valuable information. You see, when you go over a ferrous item, the threshold sound will usually null (will go quiet) momentarily. When this happens, your detector may not detect a valid target for some time after that. This elapsed time is called the recovery time and varies by the detector model used.

When you hear the threshold null out, you know you went over a ferrous item and you need to slow down and or change your sweep direction lest you miss a valuable target buried nearby the ferrous item. With a silent search machine you won't know it's happening.

Ok, now that we understand threshold, lets look at volume. This is again, just like a radio. Your detector may or may not have a volume control (separate from the threshold or tuner). If it doesn't have one, you definitely would want earphones with volume control. If you have volume control in both the detector and the earphones, then set one at max volume and set the other one to actual use conditions.

My MXT does not have a volume control but it has a very powerful (read that loud) audio amp. So, I set the volume control on my earphones to produce as loud a beep as I can without it being painful. I do this by just dropping my digger on the ground and sweeping over it and advancing the volume control until it as loud as I want, without hurting my ears.

Then I set the threshold control until I can barely hear the buzz. As a side note, if the threshold is erratic instead of stable, the Gain is too high for the ground you are sweeping. Back off on the gain until the threshold is stable. "

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Re: Any benefit to threshold in all metal no discrim?

Post by Rayc » Wed Mar 13, 2019 7:46 pm

Not sure whether Bors has experience of Minelab Safaris but he is incorrect in saying that in All Metal there are no different tones to help you: ferrous will give you a grunt, non ferrous a higher pitch. A bit more complicated than that of course but basically All Metal will will give you ALL the tones.

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Re: Any benefit to threshold in all metal no discrim?

Post by Bors » Wed Mar 13, 2019 9:21 pm

No I have not used the Safari ,apologies I wrongly assumed it was mono tone all through on All metal.

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Re: Any benefit to threshold in all metal no discrim?

Post by Zyrbalax » Thu Mar 14, 2019 9:00 am

Bors wrote:
Wed Mar 13, 2019 7:10 pm
If you dial in even more squelch, you'll start to miss some of the weaker signals from far away stations.

This is exactly how the threshold control works in a metal detector!

With a silent search machine, the "squelch" control is factory set to suppress the small signals and allow signals with a strength above the threshold setting to get through and make a "beep". If you bought a detector with an adjustable threshold (good for you!), you want to set it such that you can barely hear the threshold sound on your earphones. The sound is hard to describe, but it sounds like bees buzzing your ears. By having the threshold at this setting, right on the edge, you are guaranteeing that very weak signals (like from deep targets) will be able to get through the threshold control. This gives a machine with adjustable threshold a slight depth edge over a silent search machine, everything else being equal. This is because a very weak signal may not get through the "squelch" setting of the silent search machine.

You don't want to make the threshold any louder than what you can barely hear. If the threshold hum gets too loud, you'll miss the real small signals again. This time because they are drowned by the louder threshold buzz.
Bors, I can't thank you enough for taking the time to answer (even if partly quoting!) in such great detail. I had assumed that threshold was only there to let me know when the machine was nulling over a discriminated target, I had no idea that actually it's much more than that and I could be (probably am) missing out on some deeper signals by setting it to nil (not even "just inaudible" - I've had it all the way to zero!). D'oh! I will be changing my settings forthwith; and I can now see the logic behind using a combination of highest non-painful volume and audible threshold too, so I'll be cranking up the volume a bit as well!

I do need to get to grips with manually adjusting sensitivity too - I've had a couple of tentative attempts but think I need to research it more first.

Thank you :)
Z
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Re: Any benefit to threshold in all metal no discrim?

Post by Bors » Thu Mar 14, 2019 11:27 am

The most important thing in all this is ,If you like Using Auto then that is down to you personally . Its you that is detecting ,and if your happy doing it then that is perfectly OK to go ahead and use Auto ,after all ,its on there to be used . Minelab have said using Auto GB is more accurate than Manual GB ,but many detectorists repudiate this. After all IF it was best,why bother putting Manual on the detector.
All I`m trying to say is that people have found out through their experience ,that if your Ground is Mineralisation free ,then your OK, using Auto is no problem,but if your in mineralised ground or your experiencing fast changing pockets of highly mineralised ground ,then the chances are ,the Detector used in auto ,be it a Safari, Sovereign, CTX 3030 , etc will in the norm often over compensate as it sees it to over compensate to be on the safe side ,and it will (automatically) reduce your sensitivity to a lower level ,that it doesn`t actually necessarily have to go down to,when in reality ,if you`d had been using Manual you could have got it to work on a Higher sensitivity and will work fine ,giving you a chance of a greater pick up on the deeper target signals.
But again I must add, its all down to the user what they prefer to do ,not I ,or anyone else does ,or likes to do.

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Re: Any benefit to threshold in all metal no discrim?

Post by Zyrbalax » Fri Mar 15, 2019 8:27 am

Bors wrote:
Thu Mar 14, 2019 11:27 am
The most important thing in all this is ,If you like Using Auto then that is down to you personally . Its you that is detecting ,and if your happy doing it then that is perfectly OK to go ahead and use Auto ,after all ,its on there to be used . Minelab have said using Auto GB is more accurate than Manual GB ,but many detectorists repudiate this. After all IF it was best,why bother putting Manual on the detector.
All I`m trying to say is that people have found out through their experience ,that if your Ground is Mineralisation free ,then your OK, using Auto is no problem,but if your in mineralised ground or your experiencing fast changing pockets of highly mineralised ground ,then the chances are ,the Detector used in auto ,be it a Safari, Sovereign, CTX 3030 , etc will in the norm often over compensate as it sees it to over compensate to be on the safe side ,and it will (automatically) reduce your sensitivity to a lower level ,that it doesn`t actually necessarily have to go down to,when in reality ,if you`d had been using Manual you could have got it to work on a Higher sensitivity and will work fine ,giving you a chance of a greater pick up on the deeper target signals.
But again I must add, its all down to the user what they prefer to do ,not I ,or anyone else does ,or likes to do.
The way I see it, at the moment I have this tool "manual sensitivity", that I don't really know how to use, so it just stays in the toolbox regardless of whether it might be useful or not. So at some point (hopefully soon) I need to learn how and when to use that tool, and then practice with it, so that I can in future decide when it might be useful to dig it out and use it.

I agree it's down to personal preference, and I'll probably end up using auto 90% of the time anyway, but I'd like to get to a position when I'm choosing auto because I understand my machine well enough to know that it's the best option for the site rather than choosing it because I don't know how to properly use the alternative!

Z
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Re: Any benefit to threshold in all metal no discrim?

Post by Zyrbalax » Fri Mar 15, 2019 8:31 am

Update:

So Bors I took your comments on board and in my session yesterday I turned up the threshold so I could hear it.

Now this may be coincidence, but in yesterday's session my finds were:

Three farthings
Crooked sixpence
Ha'penny
Buttons

For the coins, up to now I've found way more ha'pennies than farthings; in fact a farthing has been an unusual find for me recently.

So I am putting this down (at least partly) to upping the threshold :)

Thank you for the advice ::g ::g ::g

Z
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Re: Any benefit to threshold in all metal no discrim?

Post by Bors » Fri Mar 15, 2019 9:12 am

Quote Zyrbalax ,... " So I am putting this down (at least partly) to upping the threshold ".

To be honest having an audible threshold ,where its available to use a threshold ,has been pretty much standard practice /procedure, since day one of the production line metal detector. If you look back in most user manuals on VLF detectors under " Threshold " ,it states "turn threshold up till you just get an audible steady hum in your ear ".

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