Threshold tone

[cymro]

There has been some interesting discussion on ground balancing and sensitivity recently. I have a question regarding the threshold level I understand why you need to hear it when hunting in discrimination mode, but do you need the threshold hum to be audible when hunting in all metal? In this mode there should be no nulling out of signals so why would we need hear the threshold tone.

Dave

 

[cymro]

-- moved topic --

 

[BarberBill]

Most detectors I'm familiar with you DO NOT hear the threshold in disc. mode although it is audible in my MXT in both modes. It should be just audible so that you can hear the slightest change in the signal from the deepest or smallest objects. In all metal, this is generally the most sensitive combination on your machine and is used because it is more reliable on targets at extreme depth than TID on machines that have it, and gives a bit more depth than the disc. setting even when set an "0" or minimum. This setting is often what was used when you read about a coin or trinket giving just the slightest whisper signal at the fringe of the machine's capability.
HH
BB

 

[Uncle Willy]

Threshold anymore on modern detectors is to establish audio for all metal and pinpoint. A very slight hum also lets you know your tector is still operating.

Bill

 

[cymro]

Thanks for the information.

Dave

 

[tab-nabit]

A sort of audio reference point

 

[Monte]

Dave, I post on a number of forums but read many others. Just not enough time to respond to them all. Since others read these but are new to metal detecting and/or don't understand what the various terms actually apply to, let me clarify a few things for newcomers.

All Metal: This is a very confusing term for many who are newer to the hobby. Logically, if there is a setting labeled "All Metal" on a detector it implies that ALL metal targets can be found with that setting. Unfortunately, this is not totally correct for some makes and models which still reject some iron and other low-conductors.

Historically, the term "All Metal" became popular about twenty-five years ago when we got our first Ground Balancing models. Where we had been dealing with the 'traditional' TR-Discriminate designs, the Ground balancing designs featured controls that allowed the operator to Tune the detector for a 'proper' Threshold setting, and then another control to adjust to the ground mineralization. Once this up-and-down adjusting was done, the result was a setting that ignored the ground matrix and would therefore respond to any metal target .... All Metal.

A true, ground compensated All Metal mode has been referred to by many manufacturers with their own choice of terms. Early on it was simply called VLF (Very Low Frequency) because it required models to operate in this lower frequency range to permit such ground adjustment. Since then it picked up labels such as GB (Ground Balance), GC (Ground Cancel), GEB (Ground Exclusion Balance), GNC (Ground Neutralizing Circuitry), NORM or NORMAL (a rather disassociated reference), and then the popular All Metal.

As a rule, when an avid detectorists talks about an "All Metal" mode they are referring to a traditionally Threshold-based mode that relies on some method of Ground balance and will respond to any metal target. Ground adjustment can be achieved by manual GB, factory pre-set GB , or auto-tracing or auto-balancing GB circuitry.

In general discussion and postings on a form, it would be good if the poster would clarify what type of "All Metal" operation they refer to because if it isn't a 'traditional', Threshold-based All Metal mode then it's a motion-based Discriminate function with little or no metal rejection ... thus, All Metal Accept.

There has been some interesting discussion on ground balancing and sensitivity recently.

Yes, and a lot that I've seen related to doing a GB with a reduced Sensitivity and then increasing the Sensitivity level after the GB has been set. That's because some models might let you hear the GB audio a little better. Others have asked about re-balancing if there is an adjustment to the Sensitivity or gain.

Personally, I try to run any detector with the Sensitivity/Gain as high as tolerable, and then GB at that setting.

I have a question regarding the threshold level I understand why you need to hear it when hunting in discrimination mode, but do you need the threshold hum to be audible when hunting in all metal?

Actually, you do not NEED to hear a Threshold in Discriminate mode of modern-day motion-based discriminating models. You do need to hear it with the older TR-Disc. or VLF/TR-Disc. models, but it's not a must with today's offerings that use a ground compensated motion Discriminate circuitry.

Thus, if a model has a mode referred to as "All Metal" that is simply a motion-based discriminate setting w/o rejection, no, you do not NEED to hear a Threshold. However, if you plan to search in a traditional All Metal mode, that IS a Threshold-based operating mode and you need to adjust the Tuner (often called Threshold) to a "proper" slight audio Threshold hum. Then adjust the Ground Balance for the general ground matrix you're hunting in, and as you search you have the audible Threshold sound for a reference.

In this mode (All Metal) there should be no nulling out of signals so why would we need hear the threshold tone.

Because in the traditional All Metal mode you need to hear the Threshold audio in order to make a proper Ground Balance adjustment.

Then, once that is achieved, you need to hear the Threshold audio to let you know if there is a weaker-sounding (smaller and/or deeper target) response. Also, you WILL hear some nulling of the audio in a true All Metal mode when you move over ground that is more mineralized than the ground you've adjusted the GB for. Nulling can also alert you to the presence of problem rocks that are more mineralized than the surrounding ground matrix you've adjusted for, or visa-versa. In other words, by listening to changes in the Threshold audio as you're searching you can tell if there are mineral challenges to deal with, or if the ground has changed significantly from where you set the GB and that a re-balancing needs to be accomplished.

Monte

 

[Elton]

I remember some of mine had a little red button on end of handle, and when the threshold started climbing it was time to reset......

 

[cymro]

Thanks Monte, I have learnt a great deal from your post, my thanks also to everyone else who contributed to this thread.

Dave

 

[ToniSteve]

Monte,
Coupled with our private discussion this is a very enlightening post and much appreciated!

Kind Regards,
Steve