- A signal flow diagram describing simple frequency modulation (FM) with sinusoidal oscillators is shown in Fig. 9.
- The carrier oscillator ``center frequency'' is
*f*_{c}and its amplitude is*A*_{c}. - The modulating oscillator has frequency
*f*_{m}and amplitude . Note that controls the peak frequency deviation. - The instantaneous frequency value applied to the carrier oscillator frequency input is given by

- When , no modulation takes place. As increases, the deviation of the carrier frequency (
*f*_{c}) increases. - Using sinusoidal waveforms for both the carrier and modulator, this modulation produces additional spectral components in the output signal at multiples of , where
*k*is an integer, as sketched in Fig.10. - Note the inherent nonlinearity of this operation ... ``frequencies come out that didn't go in''.
- The spectral components are spaced equally apart at intervals of
*f*_{m}(in the absence of fold-over). - Increasing increases the energy in the sidebands at the expense of energy at the carrier frequency.
- The Max/MSP patch fm.maxpat, shown below, demonstrates FM modulation.
- The Matlab script FM.m provides an aural and visual demonstration of the modulator's affect on the resulting FM spectrum.

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