Fact Checking Re/ Detector Processing

[cjc]

I had read in Bruce Candy's autobiography that some of the amplifier circuits he developed before coming to Halcro measured interference in the millionths of a part.  Does anyone know if these super fast new detectors are approaching that level of efficiency?  I'm trying to figure out how they do what they do...

...probably a dumb question...not my first...nor last...😆

cjc

[Steve Herschbach]

No idea on that, but I have no doubt it was Bruce’s brilliance in audio processing that paved the way for Minelabs success. At the end of day it’s all about filtering out what we don’t want to hear, leaving only what we want to hear.

[cjc]

On 5/25/2022 at 10:26 AM, Steve Herschbach said:

No idea on that, but I have no doubt it was Bruce’s brilliance in audio processing that paved the way for Minelabs success. At the end of day it’s all about filtering out what we don’t want to hear, leaving only what we want to hear.

Thanks for your reply, Steve.  Its an interesting question just how much must be going on for a machine to pass the "iron cross test" for example--seeing gold right though  a pair of crossed spikes.  The sense I get is that now there's less need  to dig half responses, as a couple of sweeps will process the good signal right up though any surrounding iron. the Legend certainly does this--it pulls up targets amazingly well.  People say  that the CTX is "slow" but the thoroughness that it processes with is amazing. 

cjc

[Dutchman4]

I'm not an expert in metal detector circuitry but I do have some background in signal processing and electronics and can add some basics.  Metal detectors transmit a signal (TX) and then receive (RX) a signal back from a target response.  The frequencies and amplitudes of those signals depends on the type of detector.  The RX signal is generally very low amplitude so it has to be amplified first before it can be processed.  The GAIN of an amplifier determines how much larger the output is vs the input to the amplifier and is generally by factors of 10x, 100x, 1,000x, 10,000x, etc.  A good amplifier will not add any distortion to the original signal because any added distortion is undesirable.  Once the signal is amplified it can be processed and analyzed.  Filters can be applied to remove certain frequency components of the signal and this is another area that the designer has to take care to remove only the undesired components of the signal and leave the desired component intact as much as possible.  The remaining signal can then be processed further to extract desired information and finally converted to an audio representation that the human ear can hear and interpret.

In the old days all of this was done with analog circuits and it took some brilliant designers to get the best circuits possible.  In the 1960's Digital Signal Processing (DSP) started to come along.  DSP provides very flexible and powerful signal processing capabilities that would not be practical with analog circuitry.  With DSP the same analog RX signal from the target is also first amplified but then it is converted from an analog signal to a digital signal by and Analog to Digital converter (A/D).  This conversion process is not perfect and some very small errors can be introduced but this is minimal with a good converter.  Once the signal is in the digital domain then DSP can be applied and the designer has many possibilities and algorithms to choose from to extract the desired information from the signal without the limitations of analog circuitry.  Then the remaining digital signal has to be converted back to analog with a Digital to Analog converter (D/A) to provide an audio representation that the human ear can hear and interpret.  This can all be done with with very compact and light weight microelectronic circuitry vs the heavy and large analog circuitry of the older technology.