White’s Electronics TDI Pro - Manual (Page 27)

TDI Pro Owner’s Guide 27
MORE ON VARIABLE AUDIO (low/high tone)
Only if the GEB FINE is ON (clockwise from OFF) will the Variable Audio
feature be active. You may then select the type of conductivity feature you
wish to use. Either low, high or both low and high. Dependability varies
with the size, shape, conductivity, and metal content of the target as well
as the type of ground mineralization. In prospecting even the form of the
gold (placer, sponge, crystalline etc.) varies, and can make the ability to
identify the target diffi cult as well.
When used for beach hunting and relic hunting, where the occurrence
of target types and alloys are more predictable, the value of this feature
might be greater. In any case the user should experiment in different loca-
tions or applications to determine the level of predictability to be expected.
With some prospecting units on the market, this function is touted as
an IRON ID feature. This is not a true description of what is happening,
and is why we will call this feature Variable Audio, as that more correctly
describes it. The audio responses heard are due to the ground balancing
system, and are actually responding to the speed at which the signal from
the target decays as the search coil passes over it.
Having tuned out the ground signal, the decay from metallic targets is
either faster or slower and does not balance out. Where it falls depends
on its size, shape, and conductivity not just whether it is gold or iron. Small
to medium gold and nickel coins (which decay faster) can react with a
high-pitch tone, while large gold, most silver and copper coins, and most
iron (which decay slower) can react with a low pitch. If you depend on
this feature to always tell you that the target is gold or iron, you could go
wrong. The majority of smaller gold reacts in a predictable way (high-pitch
tone), but very large gold can react like iron. In addition, very small nails
can react like a small nugget.