What signal characteristics in an SDR receiver signal path should be evaluated or computed to determine whether the audio output should be squelched or not? What sort of computed result should be compared against a scalar squelch "knob" setting?
I assume that for FM signals, the software should look at some characteristic in the demodulated audio data stream rather than in the IQ data stream for this determination. Is this correct?
(I am looking for algorithms, not any pre-coded solutions or circuits, as my goal is to write my SDR app in 100% Swift 3.)