Editing Frequency modulation (section)

===Demodulation===
{{see also|Detector (radio)#Frequency and phase modulation detectors}}
[[File:FM Modulation - en.png|thumb|FM modulation]]
Many FM detector circuits exist. A common method for recovering the information signal is through a [[Foster–Seeley discriminator]] or [[ratio detector]]. A [[phase-locked loop]] can be used as an FM demodulator. ''Slope detection'' demodulates an FM signal by using a tuned circuit which has its resonant frequency slightly offset from the carrier. As the frequency rises and falls the tuned circuit provides a changing amplitude of response, converting FM to AM. AM receivers may detect some FM transmissions by this means, although it does not provide an efficient means of [[detector (radio)|detection]] for FM broadcasts.

In [[software-defined radio]] implementations, the demodulation may be carried out by using the [[Hilbert transform]] (implemented as a filter) to recover the instantaneous phase, and thereafter differentiating this phase (using another filter) to recover the instantaneous frequency. Alternatively, a complex mixer followed by a bandpass filter may be used to translate the signal to baseband, and then proceeding as before. For sampled signals, phase detection, and therefore frequency modulation detection, can be approximated by taking the IQ (complex) sample and multiplying it with the complex conjugate of the previous IQ sample, <math>x[n]\cdot \overline{x[n-1]}</math>.<ref>{{Cite book |last=Shima |first=James Michael |url=https://books.google.com/books?id=Aq7uygAACAAJ |title=FM Demodulation Using a Digital Radio and Digital Signal Processing |date=1995 |publisher=University of Florida |language=en}}</ref> If the demodulated signal is sampled at or above Nyquist, this allows for recovery of near-instantaneous phase changes.