Frequency modulation is a type of modulation where the frequency of the carrier is varied in accordance with the modulating signal. The amplitude of the carrier remains constant.
The information-bearing signal (the modulating signal) changes the instantaneous frequency of the carrier. Since the amplitude is kept constant, FM modulation is a low-noise process and provides a high quality modulation technique which is used for music and speech in hi-fidelity broadcasts.
In addition to hi-fidelity radio transmission, FM techniques are used for other important consumer applications such as audio synthesis and recording the luminance portion of a video signal with less distortion.
There are several devices that are capable of generating FM signals, such as a VCO or a reactance modulator.
Frequency Modulation is abbreviated FM.