Reverse discrimination as TTF on DFX

[Ohio Digger]

I've heard of this reverse discrimination on the DFX. I can't remember which forum though. If I recall they said it was kind of like 2 tone ferrous on the etrac. But Minelab guys/gals, don't get your underwear in a bunch! I didn't say it is the same as TTF, just "kind of like". And even that I'm not sure about. My questions are - How do you set it up? What is the benefit of using reverse discrimination?

 

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[huntindog1]

I guess its in the book "Digging deeper with the DFX" by Jeff Foster


JeffH said this:

I normally run straight Mixed Mode with Tone ID off. However, I have been recently using a Reverse Discrimination MM program with Tone ID on. I am still toying with it but have had good results pulling some deeper relics and coins from some of my iron infested sights. The iron will give you low tones and the "good stuff" will give you a high tone in the non-motion mode. You have to set your Tone pretty high for this to work properly. When you hear a high note sneak through the iron sounds, time to really slow down and attack it from every angle to see if you can get a good reading on the display. The program I used below is really Jeff Foster's with a few tweaks. Don't hesitate to drop the PAG to 2 if EMI is an issue.


View attachment 756773


Da FoX said this:

The objective of "reverse discrimination" is to (1) Reverse the VDI Accept / Reject criteria so that all "bad" (ferrous) targets are ACCEPTED, and all "good" (non-ferrous) targets are REJECTED, allowing the All Metal channel to "cast the deciding vote".

That being done, and with MIXED MODE = ON, the ferrous (bad) targets will sound off with a LOW PITCHED Tone ID, and the non-ferrous (good) targets will have NO TONE. However, the All Metal Channel will sound off. So, you'll get a LOW TONE from iron targets accompanied by the All Metal channel audio. Non ferrous targets such as coins, rings, etc will produce NO TONE from the Discriminate channel, but WILL be seen by the All Metal channel, producing the All Metal Channel Audio. Targets too deep to trigger the Discriminate circuits but seen by the All Metal channel will produce the All Metal Channel Audio. If you don't like the default Target Tone on DFX (160 to 231 depending on the basic program you started with) it can be increased, but this seems like and extra step to me, since the tones you are going to get from the Disc channel at this point are all LOW.

Now - to accomplish the same thing with Spectra:

Reverse all the VDIs. Accept -95 to -1, and Reject all the VDIs from 0 to +95.
Select Mixed Mode = ON to bring in Discriminate and All Metal Audio simultaneously
Select TONE ID = ON

Now, like DFX the ferrous (bad) targets will sound off with a LOW PITCHED Tone ID, and the non-ferrous (good) targets will have NO TONE. However, the All Metal Channel will sound off. So, you'll get a LOW TONE from iron targets accompanied by the All Metal channel audio. Non ferrous targets such as coins, rings, etc will produce NO TONE from the Discriminate channel, but WILL be seen by the All Metal channel, producing the All Metal Channel Audio. Targets too deep to trigger the Discriminate circuits but seen by the All Metal channel will produce the All Metal Channel Audio. Hence, you are "digging the All Metal channel only", or "reverse discriminating".

Now, if you REALLY wanted to go to the extreme - you could reassign all the tones to the low VDIs so that -95 started with 160, and ended at -1 at 255, but to me, that would be like hitting yourself in the head with a hammer just because it feels good when you stop .... Note that with DFX the VDI / Tone relationship is fixed, so there's no reassignment options available.

Something that is often missed in the employment of this approach is the setup of the ALL METAL channel sensitivity, or DC in the case of DFX and AM with Spectra. If the All Metal Channel can't see AT LEAST as deep as the Discriminate channel, you are wasting your time. I call this "balancing the All Metal and Discriminate channels". "Properly" deployed, one should actually have the All Metal channel set to see a bit deeper than the Disc channel, but as long as they're at least "equal", you'll be OK. What some folks forget, unfortunately is to make ANY adjustment to DC / AM and wind up with the Discriminate channel "seeing" targets that can't be reported because all the non-ferrous VDIs are rejected. Or, put another way, All Metal can't see the target and Discriminate can't tell you about it.

I have never been a fan of this setup. In each case, you are depending on the All Metal channel to be the "decider" and you are depending on the All Metal channel to "see deeper" than the Discriminate channel. If I'm in a low trash environment, I want to ENHANCE the good signals with TONE ID, and not be bothered by the odd nail, etc. I'll still get benefit of the All Metal channel's depth advantage. (Note my favorite DFX C&J setup employs Mixed Mode). If I'm in a high trash environment, such as an old house tear-down site, I know it, and I don't want to hear all the nails, roofing shards, etc, etc, so I'll turn Mixed Mode = OFF to keep the chatter from the All Metal channel quiet.

All this being said - its an option, and some people like it. It is surely worth a try ...

Hope this is helpful. Da FoX