Input signals are applied to the capacitor "C". Capacitive reactance is the important factor in the analysis of the operation of a differentiator. Capacitive reactance is "X"c = . Capacitive reactance is inversely proportional to the rate of change of input voltage applied to the capacitor. At low frequency, the reactance of a capacitor is high, and at high frequency reactance is low. Therefore, at low frequencies and for slow changes in input voltage, the gain, , is low, while at higher frequencies and for fast changes the gain is high, producing larger output voltages.