Soils contain varying levels of metallic ground minerals that can affect metal detection depth. A way to minimize the effects of ground minerals is through the use of ground balance circuitry. Without getting too technical, ground balancing allows the metal detector to limit the response from the ground minerals.
Ground balance is needed because it is possible for the concentrated ground mineralization to respond like a buried object that does not exist. The audio feedback from this mineralization can hide good targets and can negatively affect detection depth. A ground balance feature will minimize the loss of depth as well as the falsing noises.
It is also important to understand that to achieve stability in areas of high mineralization, a ground balance feature will likely ignore objects that share a conductive range similar to the ground being cancelled. An example of this is the difficulty metal detectors have in finding small gold items in wet salt-water soaked sands. When ground balancing to eliminate the chatter from the saltwater, the metal detector is forced to ignore small gold items that share the same conductivity range as the saltwater.
Metal detectors can include the following ground balance configurations: fixed, auto-ground balance, manual ground balance or a combination of the three. Most entry level metal detectors include a ground balance setting that is set at the factory and cannot be adjusted without opening up the control housing. These metal detectors can perform well in mild soils, but tend to struggle in higher mineralization areas unless the factory preset reflects the soil conditions you will be searching.
Auto-ground balancing metal detectors are supposed to regularly assess the ground mineralization and automatically adjust the ground balance accordingly. Beware that some manufacturers have marketed some fixed ground balance detectors as auto. These are not the same thing.
A manual ground balance metal detector will have either knobs or buttons that allow you to raise or lower the ground balance to suit your metal detecting needs. Once set, the ground balance will not change until you again adjust the knobs. The ability to fine tune the ground balance and to run it either a little high or low can at times be beneficial. Having the option to switch between the auto and manual ground balance on the same metal detector is the way to go when possible.
One final comment on ground mineralization, it can be very irregular and inconsistent. In some locations it is possible for the ground mineralization to change drastically every couple of feet. As a result, it may be necessary to ground balance frequently in order to minimize depth loss.