By using the preemphasis filter shown below and with a voice

By using the pre-emphasis filter shown below, and with a voice signal as a modulating wave, an FM transmitter produces a signal that is essentially-modulated by the lower audio frequencies and phase modulated by the higher audio frequencies. Explain the reason for this phenomenon.

Solution

the mirror operation is called de-emphasis

and the system is called emphasis

pre emphasis is acheived with a netwrok which is essentially a calibrated filter.the frequency respionse is decided by special time constants

in processing electronic audio signals, pre-emphasis refers to a system process designed to increase (within a frequency band) the magnitude of some (usually higher) frequencies with respect to the magnitude of other (usually lower) frequencies in order to improve the overall signal-to-noise ratio by minimizing the adverse effects of such phenomena as attenuation distortion or saturation of recording media in subsequent parts of the system. The mirror operation is called de-emphasis, and the system as a whole is called emphasis.