Q.Explain with circuit the pre-emphasis and De-emphasis.

In FM the higher audio frequencies have smaller amplitude and are more affected by noise. Pre-emphasis is a high-pass RC network at the transmitter that boosts these high frequencies before modulation, and de-emphasis is a matching low-pass RC network at the receiver that attenuates them back after detection, restoring the original balance while suppressing high-frequency noise. …

[!TLDR]

Pre-emphasis boosts weak high-frequency audio before FM modulation; de-emphasis cuts them back by the same amount after detection, so high-frequency noise is reduced without distorting the signal.

In frequency modulation the noise picked up in the channel affects the higher modulating frequencies more than the lower ones, because the amplitudes of the high-frequency components of speech and music are naturally small while the FM noise increases with frequency. This worsens the signal-to-noise ratio at the high-frequency end.

Pre-emphasis: At the transmitter, before the audio is applied to the modulator, it is passed through a pre-emphasis network. This is a high-pass RC circuit (a resistor in series with the signal path and the reactive element arranged so that the network gain rises with frequency; often shown as a series R with an inductor, or an RC differentiator). It artificially increases (emphasises) the amplitude of the higher audio frequencies relative to the lower ones, so that they are strong compared with the noise that will be added in the channel. …