(1) A change in the frequency (pitch) of a signal. At low modulation rates, FM is perceived as vibrato or some type of trill. When the modulation wave is in the audio range, FM is perceived as a change in timbre. FM synthesizers, commonly found on soundcards, create sounds using audio-range frequency modulation. See FM synthesis.
(2) Frequency modulation is the instantaneous changing of the frequency of a carrier in response to a modulation signal, usually an audio waveform. As the signal voltage varies up and down as it follows the waveform, the frequency of the carrier varies up and down from its nominal unmodulated value. The FM receiver is tuned to the carrier frequency, and the received signal, after suitable conditioning, is applied to a special circuit called an FM detector, also called a demodulator or discriminator, which recovers the audio signal. See amplitude modulation.« Back to Glossary Index