Pre-emphasis & De-emphasis

Analog fm transcievers more accurately reproduce audio from sender to receiver, when the higher frequency components of the audio are amplified prior to transmitting, and then have those higher frequency components attenuated at the receive end to re-establish original levels.
Most receivers Require pre-emphasized audio, with the circuits hard wired in series to the audio amp. Higher end receivers offer a "flat" output to bypass the de-emphasis circuitry or software (dsp) by jumper or programming. |
Transmitters will have a mic input, where the audio inserted is pre-emphasized. They will also have a flat input that bypasses that circuitry or software (for data, simulcast,etc). A different input direct to the vco is used for external ctcss.
Missing emphasis on either side produces odd sounding audio to the user. For most applications, it MUST BE USED.