Inverted Audio Signal?

[thomthom]

Hi there

I recently bought a second hand cheap metal detector "GC-1005". I've tried to go through the calibration instructions from the manual (leaflet). What puzzles me is that it generates a sound when it's not near any metal. But when I move metal over the sensor and the display needle starts moving about the sound becomes lower. The stronger the signal the less sound - the weaker the signal the more sound there is.
Isn't this completely inverted? The manual appear to indicate the should detector should generate sound when it senses metal.

Might it be that I've gotten a faulty model?

 

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[SusanMN]

Sorry but I have more questions for you than answers for you. You have an detector I am not familiar with but I am wondering if the "sound" you are hearing is the threshold hum. Does your manual mention threshold? And what kind of metal are you testing the detector over? If your machine has discrimination, perhaps you detector is nulling out the signal because your detector is set to discriminate it out.