In amplitude modulation, the instantaneous voltage of carrier waves is varied by the instantaneous voltage
of modulating waves. On transmission through a channel noise signals can also be added, resulting a
change in the amplitude of modulated waves. Due to it, the receiver receives the modulating signal having
a part of noise.
However, in frequency modulation, the frequency of carrier waves is changed as per instantaneous voltage
of modulating waves. This can only be done at the mixing or modulating stage and not while signal is
transmitted in channel. Hence, noise does not effect FM signals.
