Question

why pre Emphasis and De Emphasis are used in frequency modulation but not in amplitude modulation?

Answer 1

⇔The shaping of audio on Frequency Modulation limits the frequency shifting to keep the transmitted frequency within its allowed range. The signal width audio determines the frequency swing.

⇔On Amplitude modulation, the audio is imposed on the carrier. It too has upper and lower audio range.

⇔This is why Emphasis and De-Emphasis are used in frequency Modulation but no in Amplitude Modulation.

:)