All Metal mode VS Disc Mode; A valid question (I hope)

We have all seen it. I have seen it with all of the detectors that I have had that has a DISC mode and a Autotune (or Threshold based All Metal mode). In Disc mode, even when there is NO discrimination selected, the detector cannot even SEE those ddep targets until you switch to All Metal mode. And in All Metal mode, the audio report will almost rupture an eardrum.....when just moments ago, in DISC mode with no zero discrimination, the very same unit has trouble acknowledging the target under the coil.
In the SAME UNIT, such as an F5 or Omega for instance, I can set up the DISC mode with zero actual discrimination, with Gain and Threshold set hot, and have a bullet at 11 inches. No audio indication that anything is under the coil (with 11 inch DD stock coil) but then, I switch the unit to AUTOTUNE (All Metal) and sweep over the same spot, and there is a target plainly present. Question: What is the difference between DISC mode with zero disc selected, and All Metal mode??? Why will All Metal pick up the target, even in my masking soil, when in DISC mode, with ZERO discrimination selected, there is NO audio report???? (This knowl;edge may be 'old news' to many of you, but it stumps me!!!) Thanks for any feedback.

Without going itno a lot of detail Kevin..

The all metal threshold based mode you are using is ran through just one channel...
The Disc mode is ran through 2 channel's and then compared using a process called phase shift...

the depth loss is from the phase shift technology...

The all metal is a pure raw signal...

for the f5 to call iron iron on zero disc it still has to be analyzed...

That's why a mixed mode audio is nice...all metal and disc together...it will give you that depth the disc takes away...

Keith

Yes Keith, I follow you!!!! Why can't this be done I wonder?????? I'm sure this has been looked at by engineers. But MAN, if we could have a detector with multiple tones without losing the raw depth. But something tells me that I am discovering stuff and asking the subsequent questions that have been discovered and asked for years. Man, I WISH I had a degree in electronic engineering!!! I'd just go ahead and build us one with a WARP SPEED PHASE SHIFT!!! I'd call it a Super Flash 5000.

Hey Kevin...

If it was not for Phase shift we might still be digging it all....

Thats how revolutionary it was and still is in metal detector design...

It also allows you to ground balance a metal detector...

You can thank George Payne for that...

Keith

Disc mode and ground balance allows us to pass iron up to respectable depth.
Now depth is a relative term.
Back in the early days, before ground balance or discrimination, we had BFO and TR which didn't ground balance per se.
Then we got ground balance TR without discrimination which would go fairly deep but if it got out of balance
a major depth loss was incurred.
George Payne figured out a way to ground balance and keep good depth and added discrimination and target ID.

Back in those early days, before GB and disc/ID when only a few inches could be had, there was tons of silver coins dug up out of the ground.
Through years of detecting, most of the easy accessible sites coins and relics have been removed, leaving us with the
harder to get stuff, stuff at the fringe of ID/disc detection and stuff mixed in the trash, whether the trash be iron and/or non-ferrous items.

The all-metal mode basically represents what was called in the older days "static mode" since no motion is necessary for detection.
Later on the static mode was improved since while in that mode the electronics would "drift" out of tune from the optimum setting of
background "threshold".
Then later in development came terms such as "SAT" which basically is a means of auto adjust threshold or "self-adjusting threshold".
When using this mode, motion must be used else anything directly under the coil will be adjusted to threshold.
The term all-metal motion came into being.

One of the last detectors that was made had 4 modes--the XL-Pro.
It has TR mode, Static no-motion all metal, all metal motion and discrimination mode.
While in modes other than disc mode, the meter would still read and give visual target ID.

That is a very rough going over in history and not 100% accurate but close enough for a general idea of all-metal/discrimination aspect.
What the brands are doing in software today likely can't be explained by old school terminology.

I must make a final note however about TR and BFO, some of them early on had a sort of discrimination aspect to them but
nothing like what we have today...but that is another story...

I think you will find that modern machines that do most of the work inside a DSP processor CAN achieve close to all-metal depths in ID mode. The Tek T2/Fisher F75 would be one likely 'platform', I expect the XP Deus should also do it. You need to perform heavy math on the two demodulated signals in order to achieve it (root of the sum of the squares / Pythagoras type stuff) which is impractical in analogue, and not accurate enough when done in a simple microprocessor.
Kevin - if you want to know more about the inner workings of a detector, take a look on Minelab's website, there's a couple of detailed 'How does it work?' type articles.

Years ago I had a Nautilus machine (forgot the model) that had disc in one ear and all metal in the other. The V3i also can be programmed to do that also, I think it was called "all pro audio".

Thanks guys. This is some interesting stuff. But having no formal education above 12th grade (except HVAC school for two years), most of it is in greek. I will check out those Minelab articles, Pimento!! I 'preciate that! Just as I appreciate ALL feedback.

I feel mixed mode audio of the XLT would fit your needs although well learned really works but its a bit noisy as it picks up a lot of junk along the way plus a goodie or three...

Heck go out and swing that thing and have fun as you are entering the world of paralization by analyzation.

Lets put it this way I drive my car to where I want to hunt and over the years have found some nice items such as diamond rings and coins going back to the 1700's but I sure couldn't overhaul the cars motor or tune a detector...

Certainly no reflection on you or myself but we all have limitations....

And then there was FBS and FBS2