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Threshold 
Adjusting the Background 
Audio Level
Threshold is the constant audible background audio 
tone or 'hum' produced by the detector. 
The level of the Threshold should be set low/to a 
minimum, but still audible and stable. Ideally it should 
be a smooth, gentle hum. 
Small targets or large deep targets may not produce 
a distinct target signal, but may cause only a small 
variation in the threshold. 
If the Threshold level is set too high or too low, these 
very small variations may be missed. 
Listening for a target signal with a high threshold would 
be like trying to hear a whisper within a crowded noisy 
room. A high threshold level may also be uncomfortable 
for your hearing.
If the Threshold is set too low, the target signal needs to 
be loud enough to become audible, therefore very soft 
target signals from small or very deep targets may not  
be heard.
It is important to reset the Threshold level as conditions 
change. For example, your ears may adjust to the low 
levels of audio after an hour or so, or the conditions may 
have become windy.
Turn the Threshold control clockwise to increase  
the threshold level, or anti-clockwise to decrease the 
threshold level. 
When the threshold is 
too high, a faint signal is 
masked, and only the peak 
of the loud signal is audible 
above the Threshold.
With the threshold set 
correctly, both target 
signals are easily heard.
A threshold level that is too 
low does not allow faint 
target signals to be heard.
 
Audio Range that 
you are able to hear
threshold level
 
Audio Range that 
you are able to hear
threshold level
 
Audio Range that 
you are able to hear
threshold level