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  #1  
Old 04-22-2012, 01:28 PM
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lisfisher lisfisher is offline
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Default Threshold

Hello, trying to get used to my new Safari, it's a learning curve compared to my old white's classic 3. There is a low hum sound that is constant and it would be nice to get rid of it. My question is, if I turn the threshold down to silence the hum, am I still in the same discriminate modes? In other words, will I be tuning out certain targets?
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Old 04-22-2012, 02:01 PM
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Quote:
Originally Posted by lisfisher View Post
Hello, trying to get used to my new Safari, it's a learning curve compared to my old white's classic 3. There is a low hum sound that is constant and it would be nice to get rid of it. My question is, if I turn the threshold down to silence the hum, am I still in the same discriminate modes? In other words, will I be tuning out certain targets?
This is the threshold tone.
I assume the discriminate mode will be the same, but you will probably lose the ability to "hear" smaller targets and deeper ones, too.

Also, Minelab's threshold tones "Blank out" over iron targets which is very useful information to have.

I believe this is the way it works, I am sure ML owners will chime in.

The threshold tone is a main feature of your detector.

From the manual...

The constant background ‘hum’ produced by
the detector is called the Threshold (p. 27).
Variations in the Threshold allow you to hear
very small and deep targets. It is also used
to help distinguish between desired and
undesired targets.
Sweep the coil across the targets one at
a time. Observe the LCD and listen to the
sounds of the detector as it passes over
each object. Although the LCD will give you
detailed information about the target, it is
important to pay attention to the difference
in audio response between each of
the objects.


Threshold
The Threshold controls the audible level of
sound during detecting, or the “background
hum”. Most operators find that detecting
with a very low but still audible Threshold is
preferred. A lower level may mask responses
to smaller targets and the higher levels will
make targets difficult to hear. The level preset
by Minelab is 12.

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Old 04-22-2012, 02:32 PM
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You should turn it down to barely audible, but not silent. It is the "threshold" at which the machine notifies you with a beep. If it is too low, then small targets won't produce a strong enough response, and set too high the threshold tone can drown out faint signals. With headphones, for most "normal" hunting, my threshold is usually set @ either 1 or 2.

The blanking of the threshold tone is called "null". It is something that you should read up on and be aware of, but probably won't take full advantage of until you get a bit more time under your belt with your new machine. Truly utilizing the null is a science in itself.

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Old 04-22-2012, 02:47 PM
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You need to get used to it. There is valuable information there. Some has already been discussed.

It will go silent over iron
It will go nuts with EMI
It can tell you the type of ground balance you have on other detectors positive or negative
It can tell you when to slow your swing
It will give the very deepest targets away

You went top end. Or darn near it. You need to take advantage of top end tools.

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Old 04-22-2012, 11:01 PM
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I did hear the blanking out the other day. So if I crank the theshold down just low enough to hear it, I should be ok? Going to take a while to learn this machine. I did throw 4 different coins on the ground to hear the differences in tones. Dimes screamed with a high pitch, quarters high pitched but not as high as dimes, pennies a bit lower and nickels produce a very low tone. I'll have to break out some colonial coppers and pre 1964 silvers from my collection and see what kind of tones they produce.
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Old 04-23-2012, 04:56 AM
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Default Threshold

An adjustable threshold is not a setting most lower-end detectors give you, and many do not even allow you to hear the threshold tone. In most machines used today, when detecting in a discrimination mode, the machine is quiet until you detect an object. This is not because there was nothing to hear, but simply because the background signal is not passed on to the user at all. Instead artificial tones are generated when the electronics detect a signal that it's processors deem worthy of your notice. But deep inside, the machine "hears" this constant signal coming from the coil, and decides at what point a small change in that signal is worthy of being sent to you, the user.

But all the older machines allowed you to hear this constant background noise, and it can bring in very deep or weak signals other detectorists miss. The upper-end Whites machines still have this feature, as do a few other brands, especially when they are in the all-metal mode.

Consider it as if you are listening to the raw signal from the ground, without any processors deciding for you if it's a good target or not. You decide, and it's your ears and brain that tell the difference between a change due to your swing or nearby metal surface object, and a repeatable faint whisper of change that is from a deep object.

For every positive signal you get in your machine, telling you that it found a target.. there are probably hundreds of time that the machine CHOOSE to ignore a good signal detection rather than send it to you. Why?

Because of THRESHOLD. Threshold is the level at which the barrage of background noise, be it ground signal or EMI, is ignored. You all do this automatically in everyday life. You have learned to TUNE OUT the sound of fluorescent lighting in an office, or the low hum of air conditioners. You still can HEAR it, but you have adjusted your perception to ignore it. If you didn't, then you would be barraged by so many sounds that your daily life would be painful and you could not concentrate. A metal detector's circuits do the same. They are set (or you set them) to ignore the small fluctuations in the background signal coming from the coil. But small changes in that background signal are also coming from deep metal targets, not just ground interference or EMI. If the detector has TUNED OUT (or set the threshold higher than) that small change in incoming signal, then you will never know what you just passed over. It's like you not noticing a tiny, momentary pitch change in the AC in your office.

It's impossible for a detector to tell that a small change in signal that was detected from a deep coin was any different than an identical signal change from random noise or bad ground. Only YOU, by re-sweeping the suspected target area and hearing that tone REPEAT are YOU able to make that observation and know that this was no fluke of ground noise, but a real object under the ground. You have one thing the machine does not.. eyes.

Here's a chart that shows where the threshold level should be at and why. In this graph, the blue line is the signal coming from the ground and converted into an audio wave. The spike ¾ of the way across is a weak, but good target. The bump at the far end is a very weak, very signal, down deep.

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The background hum is the state of the machine being in perfect ground balance. It's like listening to the fog of ground noise. If you turn this down too low you cannot hear the faint increase in tonal pitch caused by a weak deep signal as it just barely rises above the ground noise. If you set it too high, all you hear is background noise, which then masks out those weaker signals.

If the detector sets this level automatically, you can see (depending on ground conditions and EMI) that you can miss the weaker signals. This is what happens without you knowing it with a machine that runs silently. The machine is deciding what level of signal rises to the level of being heard - not you.

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Having a machine that allows you to hear and adjust the threshold level, puts you in more control of the machine, allows you to hear things you never would otherwise (weak signals, null, and ground imbalance) and find those elusive targets everyone else missed!

This is one reason the old White's 5800 and 6000 detectors are still very popular with the old pros and still fetch a premium on eBay. Get your hands on a White's 6000 Di Pro XL - and you will be amazed at what sounds you've been missing.

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  #7  
Old 04-23-2012, 08:57 AM
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Great explanation, I get it now. So those very faint signals could actually be good targets?
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Old 04-23-2012, 09:29 AM
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If it's repeatable, then it is a target. Whether or not you want to dig it is another question. If I'm looking for coins and it shows are being iron, then no I wouldn't. But if I am relic hunting, yes I would.

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Old 04-23-2012, 08:59 PM
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Quote:
Originally Posted by lisfisher View Post
Hello, trying to get used to my new Safari, it's a learning curve compared to my old white's classic 3. There is a low hum sound that is constant and it would be nice to get rid of it. My question is, if I turn the threshold down to silence the hum, am I still in the same discriminate modes? In other words, will I be tuning out certain targets?
I've never used a safari, but I do have a GT. You will get used to the threshold tone eventually. I've become so accustomed to it, I can't imagine using a detector without it.
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  #10  
Old 04-24-2012, 02:16 AM
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i'm the other way round. I've never heard a MD without a threshold before. if there isn't one, i feel very wrong.
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Old 04-24-2012, 04:28 AM
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i'm the other way round. I've never heard a MD without a threshold before. if there isn't one, i feel very wrong.
I'm the same...used Minelabs from the start. Awesome info in this thread by the way...

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