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Microphone Month 4

Frequency Modulation (FM)

The changing of the frequency of a “carrier” in response to a “modulating” signal, usually an audio waveform. As the modulating signal voltage (amplitude) varies up and down the frequency of the carrier varies up and down from its nominal unmodulated value. In music, vibrato is a form of frequency modulation because it is a periodic variation in frequency (pitch). In FM broadcasting the audio signal is used to modulate a high frequency carrier that is then transmitted. At the receiving end a special circuit called a FM detector, or “discriminator” is used to recover the audio from the modulated signal. FM is considered a better (than AM – Amplitude Modulation) method of transmitting radio and TV signals because the FM signal is not as sensitive to amplitude variations caused by atmospheric interference. FM is also used as a sound synthesis technique (see FM Synthesis).

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