What does IIR and FIR filter are used for in embedded

[johnwasser]

@haseebzaib

so this is the signal which I am trying to detect.
as u can see in map002 picture there is no target(by target I mean metal) available
in map003 picture there is target but on 1 feet distance
in map004 target is completely touching the coil. this is the signal I am trying to work on

in my opinion change is significant and can be detected

It looks like the rising edge of Channel 2 is the place to sample the blue line. Then just use the value to set the tone(). I would use a pot for a 'squelch' and turn off the audio if the sampled value is below the squelch threshold.