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Metal Detector Mixed Modes


Steve Herschbach

Modern induction balance (VLF) detectors usually can operate in two basic modes. A true detect everything all metal mode or a discrimination mode. Discrimination modes use various filtering methods to help separate desired targets from the trash. The filtering takes away from overall depth and the target identification gets less reliable with depth. In nearly all cases a detector operating in a pure all metal mode will find targets deeper than a unit running in a discrimination mode.

It is possible to take a detector running in discrimination mode and set it to accept all targets. You are now running with zero discrimination, and the detector now sounds off on all targets. The problem is that some detector manufacturers are labeling this zero discrimination mode as an "all metal" mode since all metals are being detected.

Unfortunately, you have not really turned off the discrimination. A true all metal mode employs no filtering at all, it directly reports a target. In zero discrimination the target is still being filtered, but you are telling the machine to report all filtered targets as good targets. The bad news is you still are losing depth and sensitivity compared to the true all metal modes.

Most metal detectors are made for coin detecting, and so most only run in a discrimination mode. You can set them to accept all targets, to run zero discrimination, but these units simply do not have a true all metal mode. All metal detectors designed with serious prospecting in mind have a true all metal mode. The reason is simple. True all metal nearly always hits hard to find targets, either very deep items or very small, better than detectors running in a discrimination mode, even when set to zero discrimination.

This is so important to me that I will rarely ever consider purchasing a detector that does not have a true all metal mode. Be careful when buying a new detector that if you want a true all metal mode you do not end up with a detector that really is offering only a zero discrimination mode. One clue is that a detector with a true all metal mode will also have a threshold control to set the audio in the all metal mode to a barely perceptible sound level. Zero discrimination modes are usually what is referred to as "silent search" modes without a threshold sound and therefore no threshold control.

It is possible for a detector to run in all metal and discrimination modes at the same time. This is referred to as mixed mode Very cool! I am not sure who first came up with this feature but Nautilus has for a long time offered units that put the all metal signal in one ear of your headphones and the discrimination signal in the other ear. More common are detectors that put the all metal output through the speaker and the discrimination signal on the meter.

The White's MXT has the Relic Mode, which is a mixed mode. I wonder how many people use Relic Mode but really do not understand it. Good targets give a high pitched chirp. Junk targets honk depending on where the discrimination knob is set. But there is a third, more subtle audio that indicates a target is there but the detector cannot identify it because it is too deep. This is the all metal signal. The meter will be blank but there will be an audio signal. When nugget detecting, you want to hear these, and dig down until the target id kicks in. I think many people focus so much on the other two audio responses that they ignore the fainter deep all metal signal. It is easy to fall into a habit of just digging only those high pitch targets. Not good.

whites-v3i-program-choices-mixed-mode.jpg
White's V3i Mixed Mode program option

The various Fisher F75 and new Gold Bug models have a basic single tone in all metal, but the meter is still active in discrimination mode. So you get the signal, then check the meter. If within range, you will see a target id. If deep, the meter will be blank. It is very similar to the old Compass Gold Scanner Pro, which had a target id meter that functioned while in all metal. The White's V3i has a very powerful programmable stereo mixed mode setting. The DFX also offers mixed mode. The new Garrett AT Gold has a true audio all metal mode while the meter is still working in the discriminate mode.

The same thing can be achieved with many detectors by running in all metal mode and then, after a target is acquired, switching over to discriminate mode to check the target. The obvious downside is that this requires lots of switching back and forth, and a mixed mode detector eliminates the switching.

The key to mixed mode is simple. Those targets in a good location that are so deep you get no indication on the disc channel are the ones you really want to think about. If the area has produced good finds but is now near to being worked out, these deep signals are the ones anyone running in a normal discrimination mode is going to totally miss. Sure, it could be trash. But really deep targets are often the best, and so digging some of these on occasion can produce some really good finds.

I have found from my personal experience that detectors often run smoother and targets are easier to hear in all metal mode. I tend to prefer a detector that has an audio all metal mode coupled with a metered discrimination mode. I just listen for the target, and once I hear it I stop and analyze it with the meter. When in doubt, dig it. Some people prefer to dig only targets that read as probable good targets as they do not like digging junk. I tend to dig anything unless it is almost sure to be junk. In other words, I dig the iffy targets. That means I dig more trash but it also means I make finds others miss. It does depend on how patient I am feeling though, and some days I will just dig those really good targets. Those are getting harder to find these days.

The only place mixed mode does not work well is in very trashy locations, especially the units that generate multiple tones. It just gets real noisy. But for many experienced detectorists mixed mode is a sort of secret weapon. Now you know why!

~ Steve Herschbach
Copyright © 2010 Herschbach Enterprises

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"Be careful when buying a new detector that if you want a true all metal mode you do not end up with a detector that really is offering only a zero discrimination mode"

I have the impression, that much of the confusion about such principles is fostered by the producers. When digging through specs and product descriptions, typically, there is not much specific technical information, if at all, and a lot of mumbo-jumbo. Detectors are instruments where it should be the easiest thing on earth to specify what they can do and what they cannot do. For some reason one could as well use dowsing rods when purchasing a detector.

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The sharp distinction between all metal and zero discrimination is getting pretty blurred.  

The original distinction was that made between an unfiltered signal, not passing through the discrimination  part of the circuit (all metal) and a signal which has passed through the Discrimination circuitry but has no discrimination applied on the variable control.(zero discrimination). This distinction was a bit further complicated by detectors whose circuits allowed full “180 degree” discrimination and those which had less range, the effects of less range was that the minimum setting still gave some discrimination.

that was then.  Now with the filtering and discrimination done mostly in software, it is much harder to be so “pure” about the distinction.

My understanding of this is based on having written a post explaining the matter the first way, only to have Carl Moreland explain about today’s realities.

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The manufacturers do damage by not agreeing on basic terms, and they often try to make it sound like they invented something new by applying a new name to something old. The "all metal" thing was fairly well understood until manufacturers started using it to mean "all notch settings cleared". For a long time PI beach detectors were noted as having "automatic ground rejection" even though they did not ground balance at all. It was merely a reference to the ground rejection inherent in a PI detector.

I believe we will see true threshold based all metal modes cease to exist per se on most new models due to what Rick has described plus the demands of the market. That is not necessarily a bad thing as newer discrimination circuits are getting the depth with simpler "beep,dig" circuits that appeal more to the average user. Riding a faint threshold has normally been the realm of the nugget hunter and such modes go unused by most detectorists. It's only oldtimers like me that find that faint background buzz comforting - many operators find a constant threshold annoying.

The latest example is Makro/Nokta referring to the Nokta Impact as "multifrequency". That term always meant simultaneous multifrequency. The Impact is actually selectable or switchable frequency and can run only one at a time. Labeling it multifrequency just threw another landmine into the terminology confusion wars. Was it a purposeful choice intended to confuse people? I hate to go that far but it does reveal at a minimum the lack of care that is taken in applying these labels to metal detectors.

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