In telecommunication, the term frequency deviation has the following meanings:
The amount by which a frequency differs from a prescribed value, such as the amount an oscillator frequency drifts from its nominal frequency.
In frequency modulation, the absolute difference between the maximum permissible instantaneous frequency of the modulated wave or the minimum permissible instantaneous frequency of the modulated wave and the carrier frequency.
In frequency modulation, the maximum absolute difference, during a specified period, between the instantaneous frequency of the modulated wave and the carrier frequency.
Frequency Modulation (FM) is a system where the amplitude of a carrier wave is held constant while the frequency is varied in sympathy with the voltage of the modulating signal.
Frequency is the Angular Velocity divided by 2 * pi.
In a strict sense, an FM signal is one where the frequencydeviation resulting from a constant amplitude modulating signal is the same for all modulating frequencies, whereas a PM signal is one where the frequencydeviation resulting from a constant amplitude modulating signal is proportional to the modulating frequency.
Sound engineers tend to refer to the carrier frequency as the fundamental frequency, but musicians often avoid this nomenclature because in music the term "fundamental frequency" is normally associated with pitch and in FM the carrier frequency does not always determine the pitch of the sound.
The frequency ratio is a useful tool for the implementation of a phenomenon that is very common among conventional instruments, that is, achieving variations in pitch whilst maintaining the timbre virtually unchanged.
If the frequency ratio and the modulation index of a simple FM instrument are maintained constant but the offset carrier frequency is modified then the sounds will vary in pitch, but their timbre will remain unchanged.
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