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Frequency modulation (FM) synthesis is a popular technique used for generating rich sound palettes in the process of sound synthesis. Initially implemented in analog systems, FM synthesizers are now implemented digitally. FM synthesizers using analog oscillators suffer from pitch instability; as a result, digital implementations are favored. The latter are helpful in creating un-pitched and metallic tones rather than standard subtractive sounds. FM synthesizers are used to create more lifelike sounds. The simple plain input waveform is changed by modulating its frequency using an FM synthesizer to create more complex waveforms for lifelike sound generation.
Frequency modulation was popularized by the DX synthesizers launched by Yamaha in the 1980s. FM techniques have been in use as early as the 1930s. However, FM synthesizers were not used until the 1970s when John Chowning, a researcher at Stanford University, developed the techniques for music synthesis.
FM makes use of at least one periodic signal (the modulator) and a carrier signal that is modulated by the modulator.
FM synthesis consists of two major components, namely, the modulator and the oscillator. The oscillator uses a sine waveform and works as a low-frequency oscillator by modulating the frequency of the carrier oscillator. The oscillator used in FM synthesis is also known as an "operator." Depending on the setup and rate of the modulation, the frequency of the carrier will move up and down as the modulation of the carrier operator is changed. This process creates different harmonics called sidebands, and the frequency of these harmonics is dependent upon the carrier frequency and how it is modulated.
FM synthesizers make use of algorithms and extra operators to create new waveforms to add more lifelike and a vibrant feel to the sounds generated. The modulating frequency must be less than 30 Hz for FM to create vibrato.