Frequency modulation
![A signal may be carried by an AM or FM radio wave.](/Images/godic/202501/29/Amfm3-en-de3455.gif")
![FM has better noise (RFI) rejection than AM, as shown in this dramatic New York publicity demonstration by General Electric in 1940. The radio has both AM and FM receivers. With a million volt arc as a source of interference behind it, the AM receiver produced only a roar of static, while the FM receiver clearly reproduced a music program from Armstrong's experimental FM transmitter W2XMN in New Jersey.](/Images/godic/202501/29/GE_FM_radio_antistatic_demonstration_19403456.jpg")
![An American FM radio transmitter in Buffalo, NY at WEDG](/Images/godic/202501/29/FM_Broadcast_Transmitter_High_Power3456.jpg")
In telecommunications and signal processing, frequency modulation (FM) is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. This contrasts with amplitude modulation, in which the amplitude of the carrier wave varies, while the frequency remains constant.