Modulation is a method of placing one signal on top of another by altering the base or carrier signal in a particular way that can be decoded to extract the additional, modulated signal. Modulation simply takes a baseline signal and alters it to carry the information of a second signal. A radio station modulates the radio frequency by altering its frequency (FM) or its amplitude (AM). he base or carrier signal has a pure, known, unchanging frequency and amplitude. It is essentially like a blank sheet of white drawing paper. The signal one desires to transmit is placed on top of the carrier. The carrier signal is altered to conform to the additional signal. Then the two signals can be broadcast or travel through wires as one – the carrier signal transporting the desired audio signal.he two combined signals are split apart at the destination and the carrier is discarded. Since the receiving device knows the shape of the carrier signal, it can delete out that shape leaving only the desired signal that had been riding on the carrier.