Filters

Anyone know about filters and how they effect a metal detector. The deus uses a 2 filter on one program and the claim is it makes the program deeper. Companies don't tell us that info or what goes into their programing for a preset even though you can change some of the setting.

LowBoy

TAKE A LITTLE TIME KICKBACK AND WATCH SOME OF MY DETECTING VIDEO'S BELOW ON YouTube

[www.youtube.com]

If you don’t dig it, then how are you going to know what you’re missing!
How can you have your pudding if you don’t eat your meat!

Hopefully NASA Tom & Geotech will chime in.
A good general knowledge topic for all.

One or two sentence answer:
The detector measures the "rate of change" of a signal. Filters determine what that "rate of change" needs to be in order to be processed as a response to you. In the past the nomenclature was 2 filter or 4 filter. New terminology describes the filters by speed measured in Hz.

And of course that will cause you to ask more questions

HH
Mike

Here is some V3 filter talk I wrote a while back.

Ground filters are used to separate out and block the slower changing ground signal and pass the faster changing target signal. White’s engineers are using hertz to designate how fast a target signal needs to change in order to pass through the filter.

In addition, they have provided two types of filters for each speed; a ‘Band Pass’ filter and a ‘High Pass’ filter.

A ‘Band Pass’ filter is exactly what it says it is. It will pass a certain signal “rate of change” that falls within or between the lower and upper ranges that have been defined for that ‘band’. It will block all signals that fall below or above that Band’s range. It will pass ONLY the signals whose ‘rate of change’ falls inside the acceptance band. It is like using “Notch Accept” only instead of notching in a metal target’s phase response, you are notching in a particular signal “Rate of Change”.

A “High Pass” filter is different than the Band Pass filter the same way the notch feature is different from the discrimination feature. High Pass is like setting the Disc on your detector. Targets below the Disc Setting are blocked, targets above the disc setting are reported. High Pass Filters block the signals whose ‘rate of change’ is less than the lower range defined for the filter and pass ALL signals whose ‘rate of change’ is above that range.
I would suggest that the upper end of all the available “Band Pass” filters are the same and that the filter speed selections allow you to raise or lower the lower limit of the Band Pass filter.

To say it another way, the Band Pass filter’s high limit is fixed. The filter speed selected moves the lower limit toward or away from that fixed upper limit Boundary.

I would suggest that a certain hertz High Pass filter and its related Band Pass filter share the same lower limit of the filter. The High Pass filter is only removing the upper limit of the Band Pass.

So…with the basics out of the way….let’s look at the filter selections…

5 Hz Band Pass = This filter is used for very low mineralized ground. Since there really isn’t a very big ground signal to block, this filter’s lower limit will allow very slow changing signals to pass. It has a high limit in place that a signal’s “rate of change” has to fall below. At this point…the mineralization effect of the ground does not significantly affect a target signal.

5 Hz High Pass = Same as the 5 Hz Band Pass except there is no upper limit.

7.5 Hz Band Pass = Now I’m starting to get some low to moderate ground response, more ground signal is received. At this point the ground signal is starting to have an effect on the target signal. This speed raises the lower limit of the Band Pass filter to compensate and requires a little faster “rate of change” from the target signal to report it as compared to the 5 Hz filter. It still has the same upper limit in place.

7.5 High Pass = Same as the 7.5 Hz Band Pass except there is no upper limit.

10 Hz Band Pass. = Now I’m into moderate to high ground mineralization. The ground response is significant. Surface irregularities will report as a metal target. The signal is degraded and weak signals are being masked by the ground signal. Surface irregularities of the ground are making the detector respond to them like a metal target. To compensate, this filter raises the lower limit even higher, requiring an even faster rate of change to pull the target signal out of the ground response.

10 Hz High Pass = Same as the 10 Hz Band Pass except there is no upper limit.

12 Hz Band Pass = High to very high ground mineralization. Weak signals are invisible and even moderately deep signals will report as iron. Ground irregulars report as metal targets. The target signal is highly degraded. This filter selection raises the lower limit to it’s maximum range to compensate. This is the narrowest Band Pass filter available.

12 Hz High Pass = Same as the 12 Hz Band Pass except there is no upper limit.

HH
Mike.

edited kHz to Hz. thanks Pimento.



Edited 1 time(s). Last edit at 10/18/2018 01:22PM by Mike Hillis.

Mike, thanx for taking the time to type all that out. It was a good read.

some a few have hardcoded filter on the deus ( gold field to name one) , but i have a custom program that is deeper than the deep factory so there might not be any filter on this one (not running in the same frequency tho)... could have been the case in the earlier version of the firmware in case if you do duplicate factory program you inherit those filter that what happened in earlier versions.

Thanks Mike!

I think it should be pointed out that Mike's post contains a rather glaring error, maybe something got lost in translation.?
All references to 5kHz, 10kHz etc should read as 5Hz, 10 Hz etc.

Put simply, if you sweep over a target at a typical 80 centimetres/second, and the target is detectable over a sweep distance of 12 centimetres ( 5 inches ), then it's there-and-gone in 1/7th of a second. Passing the (demodulated) coil signal through a bandpass filter that selects 7 Hz will tend to maximise that 1/7th sec duration signal, while suppressing low-frequency ground-signal wobbles, etc.
So that's why detectors use filters that are typically in the 8 - 10Hz range.

What about some of the older Whites 4 filters detector? Is this what makes them seam to go deeper? I have been surprised by some of there depth. flintstone

Over on Monte's forum, AHRPS Monte breaks it down like no other....Look up the subject on the Tesoro sub Forum. Good Read !!!!

Filters is what gives "usable intelligibility". The paradox is...……. with the filters invoked/employed.... you have 'perceived' better performance. Without the filters...… there is greater 'completely unusable' depth performance...… in many cases. . . . . . due to TOO much noise from various sources.