Why - Ferrous Tone While In All Metal?

[Mark Gillespie]

For over a decade I've ask for one small feature to a good detector.
Say for instance on the Fisher F75 detector or another machine of comparable abilities.
Add a two tone function in the motion all metal mode.
Nothing fancy, just one tone for ferrous and another for non-ferrous.
Being a computer programmer for several years I can't imagine this would be very difficult.
Now on the F75, while in motion all metal mode the machine gives better depth and also gives an ID for detected metal objects.
So since nothing is really needed except assigning a tone to the ID number scheme why is it so hard to acquire a unit with that feature.
I know the V3i has a feature similar, but it lacks the depth capability of the F75 in my ground.
Now I've ask again.
I'll check back in another decade.

[Steve Herschbach]

There is the MXT with the Relic mode plus the Prospect mode iron grunt feature. There are others, like the XLT, DFX, VX3, and the V3i you mentioned, the latest being the Nokta Impact. The Nautilus is the granddaddy of mixed mode units. What you are referring to is an audio mixed mode where the disc and all metal channels run simultaneously. Unfortunately the disc portion of the signal does not reach as deep as the all metal portion of the signal. In theory Fisher could divert the F75 metered response while in all metal to a secondary audio channel to create an audio mixed mode. Especially since Dave Johnson was a key engineer on both the MXT and F75 - he clearly knows how to do it. I suspect the reason it has not happened is very few people know what a mixed audio mode is and fewer yet are asking for it as a feature in new machines. Many people consider mixed mode operation to be too "busy" for general use, especially in trashy locations. It is difficult to get the audio right for more than specific site hunting or places where targets are quite sparse.

From the White's DFX Owners Manual, Page 21:

"Mixed Mode - A unique hybrid operating mode. It is an all-metal (DC non-motion, non-discriminate) mode, working simultaneously with a discriminate (AC motion discrimination) mode. It is two modes, one detecting everything and another discriminating, operating at the same time.

Discrimination Channel - When the loop is in motion, targets accepted by the discriminate program will produce a high-pitched beep. Targets rejected by the discriminate program will produce a lower pitched beep. High-pitched or low-pitched beeps are directly determined by the discrimination settings. An operator can select discriminate settings through the selection of an entire Program or by adjusting the accept and reject V.D.I. numbers in the Pro Options under Discrimination (EDIT).

 

All-Metal Channel -When the loop is not in motion, or moved slowly, all types of targets will produce the same low-pitch beep. All-metal channel will by nature detect deeper than the discrimination channel. Deeper targets will produce a lower volume sound when the loop is moved slowly over the area.

 

Tip - Advanced operators can gain extra depth by monitoring the all-metal and discriminate channels simultaneously, checking depth and digging targets too deep for the discriminate channel alone. For even more information about the target, Pro Options TONE I.D. and or V.C.O. can be added to produce a truly unique advanced users mode."

 

That last tip is a big one! For mixed mode, it is often the targets beyond disc range that deserve the most interest. You use the disc channel to pass on shallower targets and go after those unknown but very deep targets. The assumption is the deepest stuff is most likely to be great finds passed over by others using standard discrimination.

What we all are really wanting however is the full depth of a true all metal mode that discriminates to that full depth. The problem in getting there is simple. A true all metal channel only needs to tell you there is a target down there. This requires only the most minimal signal - a bare bump or break in the threshold is all it takes. A discrimination channel has to have enough phase information to make a discrimination determination. This requires a stronger signal. Any amount of detecting in bad ground will tell you target id accuracy declines with depth as the ratio of target signal to ground signal mix degrades. The deeper the target, the harder it is for the filtering circuit to tell what is target and what is ground. Eventually you get to where you know something is down there but the signal has degraded so much you/the detector can't tell what it is.

It will always be easier for a detector to say "there is something down there" then it will be for a detector to identify what that something is with any degree of accuracy. This is the reason why prospectors have for many years been digging targets at depths not seen by people who need to use detectors that have some sort of discrimination capability. Ultimately all that matters in prospecting is pure power, pure depth, and that is what the machines deliver. Discrimination always robs depth, and is frighteningly inaccurate at fringe depths, causing good finds to be dismissed as trash on a regular basis.

That is not to say we have not got machines that have been getting better discrimination at better depth. The F75 and CTX 3030 push accurate discrimination at depth about as far as it can currently be pushed. There will be improvements in the next few years as new technology comes on line. I never see the day coming however where we will get even just accurate ferrous/non-ferrous discrimination to the same depth that we can get basic target notification due to the fact that the one thing requires more signal definition than the other thing. A mixed mode scheme is as close to that as I think we will get.

The closest thing right now to what you are asking for is probably the Nokta Impact Gen (D) mode. The Impact is neck and neck with the F75 for overall performance but with additional features the F75 lacks, such as mixed mode. Whether it can equal or exceed the F75 in your particular ground I unfortunately can't tell you.

Excerpt from the Nokta Impact manual below. Gen basically allows you to run the Impact as if it is an F75 in all metal mode by setting the disc at 0. Then as you increase the disc setting, you get a iron tone for items at or below the setting you have chosen.

Gen (D) is factory preset for ferrous/non-ferrous tones. The give-away that it is a mixed mode is that you get the same tone for targets at fringe depth and discrimination effects at less than fringe depths.

Adapted from the Nokta Impact Owner's Manual, page 13:

GEN - General Search
Different than the other modes, this mode features a threshold tone which is continuously heard in the background.

General Search (GEN) mode is used in 2 different ways in the IMPACT: 1) with the Disc. setting disabled at 0 2) with Disc. enabled (non-zero). When the device is first turned on, Disc. setting will be off. When the Disc. is set at 0, the device does not discriminate targets and detects all targets (metals, mineralized rocks etc.). ID of the detected target is shown on the display (except for negative hot rocks) and the same audio tone is provided for all targets. The audio tone increases in pitch as the coil approaches the target. This is the typical All Metal mode found in most detectors.

When using the Disc. Setting in this mode, the device will emit a low ferrous tone for all targets below the Disc. Setting, and a higher tone for all targets above the Disc. setting which changes in pitch as the coil approaches the target. Let's say you set the Disc. to 20. The device will generate a low iron tone for all metals with 0-20 ID and a higher tone for all targets with 21-99 ID. Upon target detection, the threshold will momentarily go silent and only the target audio response will be heard. The duration of the threshold's silence is directly related to the level of the iSAT.

Gain, threshold and iSAT settings in this mode are optimized to provide the best performance on different terrains. You can modify these settings based on ground conditions.

We recommend using the GEN mode when more detailed discrimination is not important and not using it in heavy trash areas or areas containing many hot rocks.

GEN (D) - General Search Delta
In principle, it works the same as GEN mode. The difference is that the GEN (D) mode will generate the same tone for ferrous and non-ferrous targets at fringe depths but it will discriminate the shallow ferrous targets by emitting a low iron tone.

[Steve Herschbach]

From Garrett AT Gold Owner's Manual, page 24:

"While in ALL METAL Mode, the AT Gold will respond to the entire range of conductive and magnetic properties encountered, including ground responses. The user is continuously hearing what the searchcoil is "seeing" in the ground. Therefore, it is essential to be properly ground balanced while operating in the ALL METAL Mode. Naturally occurring minerals in the soil must be canceled out during the ground balance procedure in order to detect only the signals from metal objects in the ground.

The ALL METAL Mode provides complete target information, including a Target ID pixel on the upper scale, Digital Target ID, and depth reading. The AT Gold thus allows the operator to remain in the ALL METAL Mode at all times, in contrast to some detectors which require the operator to switch to a Discrimination mode to obtain Target ID. Be aware that some deeper targets (faint audible signals) may exceed the reach of Target ID.

Because the ALL METAL Mode permits no discrimination, the detector will give an audible signal to indicate every piece of metal it scans over. Target responses will normally be heard as a proportional Medium Tone. However, the AT Gold is a unique All Metal detector in that its Iron Discrimination and Iron Audio™ features can be used to hear if detected targets are ferrous, as indicated by a low tone. Iron Discrimination levels can only be adjusted in the ALL METAL Mode if the Iron Audio feature is on and these changes will not be retained when the detector is switched off. (See Iron Audio section, pages 30–35.)"

Page 35:

"Iron Audio Use in ALL METAL Mode: In the ALL METAL Mode, all metallic targets encountered by the AT Gold are normally identified by a Medium Tone. The use of the Iron Audio feature, however, allows the introduction of a Low-Tone response to audibly indicate the ferrous content of targets. This Iron Audio feature in a True All Metal Mode metal detector is a Garrett exclusive!

The Iron Audio feature should be used in the All Metal Mode as a means to check targets for iron content. Therefore, it is not recommended to hunt with the Iron Audio feature continually switched on.

To fully appreciate All Metal Iron Audio, use an iron nail and a coin to experiment. Select the ALL METAL Mode, temporarily switch on Iron Audio, and set the IRON DISC to 35. (Note: Iron Audio must be switched on in order to set Iron Discrimination in the ALL METAL Mode.) Switch Iron Audio back off and pass the nail over the searchcoil. The nail will respond with a clean Medium Tone, similar to that of a good target, such as the coin. Now, switch on Iron Audio and separately pass the two targets completely over the coil again. The distinctive Low-Medium-Low response of the nail now indicates a target that is unmistakably iron. Note that the coin, however, continues to respond with a clean Medium Tone."

The AT Gold function above is a type of mixed mode, layering a disc channel response over the all metal channel. As usual the ferrous indications do not reach as deep as the all metal channel.

The Minelab X-Terra 705 has a similar function in the all metal Prospect Mode which Minelab calls Iron Mask. However, instead of producing a tone the Iron Mask function causes the audio to break up or blank completely on ferrous targets. The Iron Mask setting is adjustable. Lower settings will call more ferrous items good but at less risk of accidentally calling a gold nugget ferrous. Increasing the setting rejects more ferrous items but increases the chance a non-ferrous item will be incorrectly rejected.

The XP Deus Gold Field program has their own version of Iron Mask called Iron Amplitude Rejection (IAR). From the XP Owner's manual, page 9:

"The program No 10 GOLD FIELD uses another discrimination method, called IAR (Iron Amplitude Rejection): the range of discrimination can be applied from 0 to 5. It applies only to targets that produce strong signals – typically shallow ferrous items. It will not reject deeper targets which may come across as ferrous when they are buried in mineralised ground, to ensure good targets are not rejected by mistake. Higher discrimination values, enable the detector to reject deeper ferrous. Gold nuggets buried deep in mineralised ground can generate a similar signal to a ferrous item, so in this case it is better to reduce the level of discrimination."

All White's Goldmasters have an "Iron Grunt" feature that operates at a relatively safe level of "bias" and gives a broken low tone on ferrous targets while in all metal mode. The GMT refined this by adding a "Probability Meter" that is an early version of the "Confidence Meter" seen on some other models these days.

From White's GMT Owner's Manual, page 12:

"Iron I.D."GRUNT" ON - IRON I.D. information is obtained by using the trigger switch under the display pod. Locking the trigger forward adds sound to the IRON I.D. system. Now when the search coil passes over an iron target, a "GRUNT" sound is added at the tail end of the normal metal target zip-zip sound. The alert "GRUNT" is triggered when the % probability of the target being IRON reaches 85% to 95%. The trigger locked forward for audio alert does not change any function of the system, it just adds sound. ALL targets will be heard with NO LOSS OF DEPTH.

Trigger Squeezed - Iron I.D."GRUNT" ON -  While the trigger is squeezed, the GMT IRON I.D. system performs a very unique function. Normal tracking STOPS and IRON I.D. adds each successive pass to its memory bank. Unique to the GMT, we call this feature "TARGET ANALYSIS". Since tracking stops during this process with the trigger squeezed, this analyzer cannot be utilized while searching. It is only used to"TEST" a suspected IRON target. It is also important to make long enough passes over the target to include the ground in the search field. This allows the detector soft ware to perform an accurate analysis. The sweep should be wide enough for the coil to completely leave the target. 1 1/2 to 2 feet is adequate for a small shallow target, wider for deeper, larger targets. This is DIFFERENT from most other metal detectors you may be accustomed to, which use a conventional discriminator to attempt to identify iron. The main thing is not to hover or dawdle over a target while analyzing. As with the "locked forward position", the "squeezed" position also functions while in MANUAL Ground Balance.

NOTE* THE VISUAL IRON I.D. SYSTEM IS OPERATING IN ALL THREE TRIGGER POSITIONS. The % of Iron Probability is indicated on the display by a left to right bar graph. This system is totally independent of the Audio Alert System."

The White's MXT offers the same Probability Meter and Iron Grunt features as the GMT when operated in its Prospecting Mode. There is a benefit in that the MXT is running at 14 khz instead of the 48-50 kHz of the Goldmaster/GMT models, making this a potentially more useful mixed mode function for general coin and jewelry detecting. The GMT runs too hot for many general detecting purposes. While the MXT is operating in the Prospecting Mode, iron targets 80% and over produce an audio grunt when detected.

The new White's MX Sport shares many features with the earlier MXT models including the Iron Grunt while in all metal mode. From the MX Sport Owners Manual, Page 26:

"Iron Grunt - In the All Metal modes, when the MX Sport is sure the target is iron, the iron grunt feature can speed detection by making it obvious the metal is iron. Strong IRON type responses are assigned a distinctive “GRUNT” sound.

To turn on Iron Grunt: Assure you are in an all-metal program: All Metal, Relic, or Prospecting. Press Options and select Iron Grunt with the up and down arrows. Use + and - to select 1 = Iron Grunt, or 0 = OFF (no iron grunt)."

[Mark Gillespie]

Thanks Steve, as always a very detailed answer to questions.

 

 

[Steve Herschbach]

Thanks Mark, it was a great "trigger question". Certain questions trigger my own curiosity and send me on a research mission. I am not done with this one as I want to see how many detectors are employing audio mixed mode schemes and how they are going about it. I am one of those that finds many audio mixed mode schemes to be "busy" and so the metered mixed mode scheme used on the F75 or Gold Bug/F19/G2 variants actually works well for me. I do like the Impact offering both options however and will be experimenting more with that. I am also curious now the give an AT Gold another spin. The AT Gold method has a problem however in that it has a dual tone response, and in thick trash you can't discern single tone from dual tone responses - it is even busier than most mixed mode systems.

If busy audio is the issue perhaps the iron mask function as employed on the X-Terra 705 or DEUS is the better answer. Mixed modes have been most often employed on prospecting machines but offer intriguing possibilities for other types of detecting.

Anyway, I have been editing and adding to my original responses as I find more information.

The MX Sport is another model that has this feature that is worth a hard look. Even through all the teething pains the one mode everyone praised was the all metal performance which employs the "iron grunt" feature derived from the GMT/MXT.

[Steve Herschbach]

More ruminations on mixed mode. The classic use of mixed mode is to get the full possible depth out of a detector, which you get by using the pure unfiltered threshold based all metal mode. By employing a disc mode in parallel you get discrimination for as far as it will reach, but still get notification of targets deeper than the disc mode will reach via the all metal channel.

For me as as a prospector the depth thing is paramount. There is however another issue that rears its head when you are trying to cover a lot of ground. This is normal in prospecting but also something I ran into while in the U.K. hunting large farm fields.

Disc modes compress the detector search field, often on purpose, and especially on detectors designed with quick recovery for hunting in dense trash. Powerful all metal modes by comparison have inflated search fields with fewer internal gaps between windings and that not only extend under the full coil but reach beyond the perimeter of the coil.

In practice what this means when hunting for widely scattered targets in huge open areas is that you have a better chance of missing a target completely while in disc mode. All metal is like having a larger coil so that you get better ground coverage, with less chance of missing the target. This is why I prefer running in some sort of mixed mode while prospecting or for places like the U.K. where we hunted the largest farm fields I have ever seen. The main goal is to just get the target and worry about what it is second.

For this type of hunting I find I prefer the metered mixed mode system where the audio is pure, clean all metal, then go to the meter for target analysis. My ear works better with pure all metal whispers than the much more complex audio offered up by most audio mixed mode systems. When I have used audio based systems the simple iron grunt offered on the GMT/MXT has been as efficient for me as any.

The problem with any use of mixed mode is that it can lead to "analysis-paralysis". With metered systems you obviously need to stop and check the meter. Even audio systems make you stop and analyze. Working with mixed mode exposes the flaws in the disc channel and reveals to the user just how flaky disc responses are on fringe targets. No problem with shallow stuff, but mixed mode users are often chasing fringe targets. I find I have to stop, and hit the target with careful sweeps. The coil gets closer the the ground, I get better centered on the target, and I may employ faster or slower sweeps to enhance the disc signal. This is all machine and coil dependent and has to be learned in field. The idea is to see if you can get a hold of enough disc channel signal to make a definite "no dig" decision. People approach this different ways. Some look for even a single ferrous reading to decide to pass on the target. They look for reasons not to dig and try to coax a non-ferrous reading out of the target. I however look for reasons to dig, and so try to coax even a single non-ferrous reading out of the target. For deep targets that refuse to give a disc reading, it boils down to the ground you are on and how lucky you feel. The methodology shifts depending on the situation and the ratio of ferrous to non-ferrous actually being recovered.

The point I am trying to make is that whether meter based or audio based, there is some need to work the target while employing mixed mode. This may be counterproductive, especially in dense trash. Often the key to some hunts is the number of non-ferrous targets recovered per hour. Taking too much time to analyze each target can slow you down while the person employing a cleaner disc mode just scarfs up the easier to obtain more obvious signals. Mixed mode is more for cleanup work or careful hunting of small areas, and favors those who like to hunt methodically. It is also great for large area/sparse target scenarios where target acquisition is most important.

For very many people under many circumstances however audio mixed mode is no magic bullet and many people just don't like it as not fitting their style. That is why it will remain a Pro option only offered on select machines, and not something seen on most mass market units.

[Mark Gillespie]

10 hours ago, Steve Herschbach said:

I am one of those that finds many audio mixed mode schemes to be "busy" and so the metered mixed mode scheme used on the F75 or Gold Bug/F19/G2 variants actually works well for me

Your statement above is exactly what I'm thinking.

I had the Deus for 2 years and the gold field program didn't provide the true motion all metal mode I was looking for.  It was not as deep as the F75, but a nice light machine to swing.

The F75 and gold bug provides the kind of audio I am looking for.  But like I stated 1st Texas never replied to my request over 10 years ago, way before these other machines came on the market.  Thanks for all you hard work and research.  

I just keep holding on and hoping they will release another flag ship detector, like the F75, before the market is flooded with all these other detectors.  Sometimes timing is everything.

 

 

[Steve Herschbach]

Hi Mark,

I misunderstood, I did not know it was Fisher specifically you were waiting on. There can be luck in waiting for the industry as a whole to finally produce something we are looking for, but to get specific things from specific companies can be near impossible. They all have certain ideas about what is and is not important in a detector. For instance, Tesoro is not big on tones, and First Texas generally eschews ground tracking. 

I have to admit there are enough mixed mode options on the market to suit me. I am waiting on the next step that bypasses the issue. Add effective ferrous disc to a GPZ 7000 or something similar and nobody will want to fool with mixed modes anymore.

[Mark Gillespie]

13 hours ago, Steve Herschbach said:

Hi Mark,

I misunderstood, I did not know it was Fisher specifically you were waiting on. There can be luck in waiting for the industry as a whole to finally produce something we are looking for, but to get specific things from specific companies can be near impossible. They all have certain ideas about what is and is not important in a detector. For instance, Tesoro is not big on tones, and First Texas generally eschews ground tracking. 

I have to admit there are enough mixed mode options on the market to suit me. I am waiting on the next step that bypasses the issue. Add effective ferrous disc to a GPZ 7000 or something similar and nobody will want to fool with mixed modes anymore.

I agree.

 

[johnedoe]

Steve...

Have you spent much time working with the V3i stereo mixed mode?

I pretty much use it all the time now that I have gotten used to it.