Garrett AT Pro Owner's Manual page 10

Audio Target Response Comparison: Standard vs Pro Mode
Shallow coin
Notice the differences in Standard binary audio versus PRO audio in the two
target scenarios above. The binary audio gives a solid, consistent beep for
both the shallow and the deep coin. In contrast, PRO Mode's proportional
audio provides a stronger signal for the shallow coin and a softer signal for
the deeper coin. The actual profile, or signature, of the target's response is
heard, thereby providing more information.
16 Garrett Metal Detectors
Deep coin
Adjacent Targets Comparison: Standard vs Pro Mode
Adjacent targets
These two adjacent coins would produce one strong signal while in STD Mode.
In PRO Mode, the proportional audio provides two peaks of audio response to
allow the user to identify multiple targets.
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AT Pro™