FM Vibrato

FM synthesis can create a vibrato effect, where the instantaneous frequency of the carrier oscillator varies over time according to the parameters controlling

• the width of the vibrato (the deviation from the carrier frequency)
• the rate of the vibrato.

The width of the vibrato is determined by the amplitude of the modulating signal, $A_m$. The rate of vibrato is determined by the frequency of the modulating signal, $f_m$.

In order for the effect to be perceived as vibrato, the vibrato rate must be below the audible frequency range and the width made quite small.