Frequency modulation (FM) 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 trasmisssion, FM techniques are used for other important consumer applications such as audio synthesis and recording the luminence portion of a video signal with less distortion.

There are several devices that are capable of generating FM signals, such as VCO or a reactance modulator.Frequency modulation can be regarded as phase modulation where the carrier phase modulation is the time integral of the FM modulating signal.