The process of recovering the audio signal from the modulated wave is known as demodulation or detection.

At the broad casting station, modulation is done to transmit the audio signal over large distances to a receiver. when the modulated wave is picked up by the radio receiver, it is necessary to recover the audio signal from it.The process is accomplished in the radio receiver and is called demodulation.

NECESSITY OF DEMODULATION

It was noted previously that amplitude modulated wave consists of carrier and sideband frequencies. the audio signal is contained in the side band frequencies which are radio frequencies. If the modulated wave after amplifications is direct fed to the speaker as shown in the above figure, no sound will be heard. It is because of current tends to move it in the opposite direction i.e. diaphragm will not move at all. Consequently, no sound will be heard.

From the above discussion, it is concluded that audio signal must be separated from the carrier at a suitable stage in the receiver. The recovered audio signal is then amplified and fed to the speaker for conversion into sound.