Pre-emphasis:
It is the process of boosting the relative amplitudes of high frequency components of modulating signal.
It is done at the transmitter to boost modulating frequencies above 1KHZ. RC high pass filter or differentiator is used as pre-emphasis circuit.
This circuit increases amplitude of modulating signal with increase in frequency.
De-emphasis:
It is the process of attenuating relative amplitudes of high frequency components of the modulating signal.
It is done at the receiver. It is a lowpass filter or an integrator. It produces lower output at the higher frequencies because the capacitive reactance of capacitance decreases as frequency increases.
