White’s Electronics TDI - Manual (Page 28)

8 PulseScan TDI Owner’s Guide
MORE ON VARIABLE AUDIO (low/high tone)
Only if the Gnd Bal toggle is set in the on position will this 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 min-
eralization. In prospecting even the form of the gold (placer, sponge, crystalline
etc.) varies, and can make the ability to identify the target difficult as well.
When used for beach hunting and relic hunting, where the occurrence of certain
targets can be more predictable, the value of this feature might be more useful.
In any case the user should experiment in different locations 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. What is
really going on, is the audio responses heard are a by-product of the ground
balancing system, and are actually responding in a particular way 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. Most smaller gold reacts in a predictable way,
but very large gold can react like iron. In addition, very small nails can react like a
small nugget.
The Variable Audio feature can be interpreted by the tone which it produces when
going over a target. As the search coil passes over a detected target, the signal
will get louder as it gets closer to the center of the coil, but the tone will rise or fall
depending on the decay speed.