Why is de-emphasis used in FM communications receivers?

In amateur radio, most voice 'FM' transmitters actually use phase modulation (PM) or pre-emphasized FM. In true phase modulation, the deviation of the signal increases as the modulating audio frequency increases, meaning higher-pitched audio naturally produces a wider deviation. To make the received audio sound natural rather than excessively shrill, the receiver must reverse this high-frequency boost. This reversal process is called de-emphasis, which rolls off or attenuates the higher audio frequencies at the receiver's output to restore a flat audio response. Therefore, de-emphasis is used in FM communications receivers primarily to maintain compatibility with transmitters using phase modulation. Distractors involving impulse noise are incorrect, as reducing impulse noise is the job of a noise blanker or limiter.