Frequency modulation

Frequency modulation, one of two chief methods of sending sound signals on radio waves. More commonly referred to as FM, the frequency of a radio wave is adjusted higher or lower to match sound vibrations. This kind of signal may also be transmitted along two paths, or channels, to provide stereo broadcasting to a listener who has the appropriate radio receiver. Invented by Edwin H. Armstrong in 1933, FM is also used in television and long-distance telephone systems.

See also: Radio.