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Registered: 23/05/12
Posts: 134
Reply with quote  #1 
Trying to explain threshold isn't the easiest thing in the world, this is the fourth time I've written this piece.  There are three ways to have your threshold set: too high, too low and just right.

What the threshold does is to set the barrier that has to be broken in order that a signal makes it through to our ears.  Being set too high or too low moves that point, both being equally detrimental to our finds rate and robbing us of depth.

On the Blisstool the threshold runs from 1 - 10 and the manual tells us that 5 is a good number.  It IS a good number but it needs to be finely set otherwise we start losing that depth and we start missing good signals.

The ideal setting for every machine depends on two variable, the ground and the user.  Where the Blisstool wins it is has the ability to compensate for the user in two ways; tone and volume.

The tone will help you because as we get older we become less able to hear higher pitched sounds.  So set it to as low as it can go?  No.  Lower sounds are of a lower frequency and the lower the frequency is then the less sensitive it is to variation.  So set the Blisstool to the highest pitched sound that you are comfortable with.

Again, as we get older we get a bit mutton*.  The Blisstool has you covered though because it has one of the best volume outputs I've ever experienced on a detector.  Set it to a level that your comfortable with but if you are using headphones with built in volume controls, don't set it high and use the headphone  volume to moderate it, you will lose the smaller signals.  Set your headphone volume on full and use the volume on the machine.

Now, back to threshold.  The threshold is setting the point at which the signal becomes audible.  Too high or too low has exactly the same effect - you'll miss small signals and deep signals.  What you want to hear is a low level, constant hum.  If the hum is too high then the bigger or shallower the signal has to be in order to break through that hum and become heard in it's own right.  If the threshold is too low then again, the bigger or shallower the signal has to be to make itself heard.

The Blisstool is the same as every other detector, it measures the difference between background noise and what you want to hear.  The threshold is a bit like one of the old swing-needle meters, it needs to be adjusted to it own datum (zero)  Turn the knob too far to the left and the needle sits on the bottom, below zero and it takes a hell of an input to get it to move.  Set it too high at say 9 and all the signals below that are lost, it takes a hell of an input to move it further.  The closer to zero you set it, the more sensitive the machine becomes.  In fact, after an hour or so of trying to work out how to best illustrate how threshold works I think I've just found it!

The swing-needle meter is the ideal simile, what you are looking for is for the needle to be set at between 0 and 0.1, 0.1 being the point at which the threshold hum just about becomes audible.  If it is set below 0 then any signal will have to be large/shallow enough to move the needle up to "0" before it is heard.  If it is set above "0", say its set at "2" then any signal between"0" and "2" is equally lost.

Just silent or a very low level hum, that's where the best sensitivity and best depth are to be found.

I hope this helps someone 'cos it's done my noggin in trying to explain it!

*Mutton = Mutton Geoff, deaf.

Forum Moderator
Registered: 26/03/12
Posts: 1,251
Reply with quote  #2 
Hello sheddy,

Excellent post and thank you for taking the time to explain.
 Your analogy of the threshold is spot on and as you say get the threshold right or there about's and it certainly delivers.

Registered: 23/06/12
Posts: 4
Reply with quote  #3 
Think l got it . but l struggled a little bit. many thanks.   Hutch.

Registered: 27/03/12
Posts: 212
Reply with quote  #4 
Thank's for taking the time to explain Sheddy, your analogy using the (swing-needle meter) at the end was very, very good.

Hope you have saved this explanation (I have) coz it will rear it's head from time to time

Is it ok to quote you?


Registered: 23/05/12
Posts: 134
Reply with quote  #5 
I don't mind mate, Daryn's forum, Daryn's content.  It's his call.

Registered: 05/04/12
Posts: 127
Reply with quote  #6 
A text book explanation, well done Sheddy, I am so glad you had to write it and not me 

I think that will help a lot of people.
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