An impossible and insane thought ???

[Pennypacker]

I understand binaural (crossfeed) and understand that you are a fan of it, but I fail to see the direct benefit using it in a traditional MD setup, which in a sense generates an mono signal.

Where this effect could be useful, is in a detector that uses the multiple search coil approach. But even there you would want true "stereo", and may use a bit of crossfeed for some comfort.(Releiving extreme stereo separation) By having multiple detection points, this would allow you to identify which side each target was on.

Let's say you had a silver coin 5" to the left of a nail. Now you take a swing from left to right. The first thing you would hear is the silver in the right speaker. As your swing progresses the silver can be heard in both left and right speakers as well as the iron entering the right hand speaker, then the last thing you would hear is the iron in the left as the coil leaves the target area.

The brief moment when the coils are over both targets, or targets that are closer together, you would hear the multiple frequency, simultaneous tones. Chords.

I suggest using something like one octave of a Hepatonic scale, which has 7 pitches per octave. (C)D-E-F-G-A-B-C Of course the actual notes could be customized for user preference.

Try it out here http://www.bgfl.org/custom/resources...2/music/piano/ Press the button on the left for "Chord mode". Select D and C1 which would represent iron and a high conductor like silver.
Press play chord. This is the signal I want to hear on a complex target that has both materials present.

Now lets add a gold ring to the mix, now select "F" and press play chord. It's still easily apparent that I have three distinct materials present in this complex target.
Even adding a fourth note works. After that point it gets harder to tell, but quite frankly if you have that many targets present you need to dig them up so you can separate them better.

Now this type of discrimination would be useful with or without the Left/Right location abilities I discussed early on.

[Davor]

@Skippy, you can check the LF project page with many details of my tone generation approach. Yes, it is sine with good THD.

@ Pennypacker, I fell for IGSL approach to discrimination where two independent discrimination channels are encompassing the all metal space, but dividing it into a lower tone for (mostly) Fe and higher (mostly) Cu tone, enabling either overlap or notch in a middle. I learned to appreciate this because I get all the information. It is especially useful with thrash, where electroplated steel responds as both iron and coloured. There is no way to reject it, so this is much better - I know exactly what it is and I can go on without much hesitation. In overlap tone setting it gives clear dual tone representation of foil/gold, and it is also beneficial.

I could go for more tones, but IMHO 2 are just fine for limitations of human perception. More than that would trod deeply into diddle-doodle land.

[Pennypacker]

I will see if I can find it and have a look.

[mcgov51]

*Overtheedge - By nature I am tenaciuos for sure . . . can't help it. I am also an unafraid truth teller
as I see it . . . and I don't need any help in interpreting what I see.

*Overtheedge (only) - Would you buy a New 2013 Cadillac at todays price levels if it still had drum brakes
and 2 ply tires on all four wheels and a big V-8 ?

Yes this thread has gone on longer than even I expected ? But . . . everyone has right to comment.
I now see promising suggestions being made in earnest . . . don't you?

My particular failing . . . in all of this is . . . I am am not an Engineer or Scientist or MIT PHD . . .
so . . . I must endure the lumps a dummy like me deserves for bringing up such a thing.

My hope is that the right person with the right desire and knowledge will pursue one or more of these ideas?
And I am sure Carl and other ADM's still invites others to chime as well.

And like yourself I am also 62 (retired) and work hard at what I love ?
MD'g to me is an all day thing.

Cheers / Best Wishes

[mcgov51]

Davor . . . Sounds Impressive ? . . . and not just to me ?
Please continue . . . best of luck.

[Pennypacker]

I think I am going to pull-chute on this thread.

Have fun.

[Ferric Toes]

I built a one off PI for water hunting using three audio tones - high tone for early sample, medium tone for middle sample and low tone for late sample. The idea was that for a thin ring only the high tone would sound; for a medium ring, coin, etc. both high and medium tones would come on, and for long decaying signals, plus iron, you would get all three in varying proportions. The tone frequencies were arranged so that there was harmony between them, and with all three it sounded like a chord. Was it any good?

After a couple of outings on an old swimming area, the customer shut off the last two tones and just listened to the one for the early delay. Reason - the small threshold tremble with no signal was a plus and minus mix of three tones going in all different amplitude directions. OK when a reasonably positive signal was detected, but otherwise he wanted to rip the phones off after 5 minutes. With the amplitude dependent single tone he found many gold rings in that area.

Motto - think what noise is going to sound like as well as a good solid signal. You don't want to simulate a killer bee buzzing around inside your head.

Eric

[mcgov51]

Oh Ferric - I agree and I think/hope we all agree.
My goal/joy . . . is to someday . . . see someone put a muffler on that locomotive.

Afterthought: There is technoloy out there that can cancel noise by bombarding it
with a different noise designed exactly to do this. Anyone . . . ?

PennyPacker - You're still in the box . . . unless you want to cry uncle.
I've seen bits and pieces within some written articles over the years that dealt with this.

[Carl-NC]

McGov, no need for add'l provocation.

There are so-called noise-canceling headphones which reduce noise generally by using differential microphones. We can use this trick in metal detectors with a differential "coaxial" coil. In fact, it's been done since the 70's. But there are other drawbacks, so coaxial coils are usually relegated to specialty hunting.

There is otherwise no "noise canceling" panacea. True noise tends to be random and wideband, and unpredictable.

[Davor]

Well, maybe there is something to it...

I'm not completely unscathed by VLF listening and whistler frenzy, so there might be some bit of noise cancelling niche after all. VLF (and LF) are greatly affected by impulse noise.

I earned my dipl.ing. promotion suit money by a Rector's award on a paper about noise blanking. You can safely say that vast majority of chatters originate from various impulse noise sources in VLF/LF bands, hence a good noise blanker would enable you some extra dB-s of gain and depth.

Point is that you can expect downright miracles with noise blankers when applied in noisy bands. Heck, I was able to complete a decent QSO in a completely closed band just by engaging a (corrected) noise blanker on a FT101E with stations 12700km right underneath me. Effect ranged from none at all to over 20 dB improvement. I learned then that practically all of the noise above thermal is in effect impulse and can be reduced using blankers.

[WM6]

Point is that you can expect downright miracles with noise blankers when applied in noisy bands. Heck, I was able to complete a decent QSO in a completely closed band just by engaging a (corrected) noise blanker on a FT101E with stations 12700km right underneath me. Effect ranged from none at all to over 20 dB improvement. I learned then that practically all of the noise above thermal is in effect impulse and can be reduced using blankers.

Hi Davor, can you say something more how this noise blanker work, if there simple and relative cheap solution exist, of course?

[Davor]

In my case it all started with FT101E TRX when I found that the noise blanker in it was not functioning because one diode was placed in reverse, so the poor thing did not blank at all. Once I turned it the right way the blankers got my full attention.

There's not much to tell. Blankers attempt to detect an impulse by means of their short lived nature. In wider bandwidth filters pulses gain amplitude, while coherent signals remain the same. Wider band also means a faster response, so there's your time advance. In narrow band filters pulses lose amplitude, but gain duration and get delayed by means of group delay. Coherent signals do not change amplitude with filter bandwidth. Hence a successful impulse noise blanker must be able to detect a pulse just a little bit faster than the normal signal path group delay. Such detection triggers a gate that stops propagation of a normal path signal for the time a pulse would take after wideband filtering, a monostable. Because such blanking events are shorter than information rate, and the fact that narrow band filters also reconstruct a great deal of a missing signal continuity, the effect is as if the impulse noise is just not there and S/N improves.

Some commercial AM receiving chips have a noise blanker included with monostable, gating and all, but what you must supply are the filters that will make it tick, and filter choice is not entirely trivial. This approach can be fairly easily applied to detectors with bilateral switches that have the "inhibit" pin, such as 4053, and more than one filtering stage prior to the switches to ensure proper delays. These would require only additional noise detector with monostable, and inhibit pin would need to be plugged to it.

[mcgov51]

My mind was always open to a possibility like this.

Davor . . . please continue to immerse yourself into this . . . you have a special gift my friend.

[Davor]

... or not

I did not foresee any need for noise blanker for my future LF rig as LF is not affected by impulse noise as VLF is, and there are considerably less impulse noise sources in wilderness than in "civilisation". I'd include a noise blanker in a device that is supposed to operate in settlements and near powerlines. Besides, many rigs are not capable of benefiting from such SA/N improvement as they are deaf. Mostly because of over-zealously cranked up antichatter filters.