PRE-EMPHASIS NETWORK

Transmitters and Receivers Glossary

Transmitters and Receivers — Pre-Emphasis Network

Information on Pre-Emphasis Network

The pre-emphasis network is the first half of a system consisting of a pre-emphasis network in the transmitter and a de-emphasis network in the receiver. The pre-emphasis / de-emphasis system reduces frequency-modulated noise that affects the signal during transmission or at the front end of the receiver. The noise spectrum from an FM detector varies linearly and increases with frequency (rising at about 6 dB/octave). The noise therefore affects the high frequencies, the distortion of which dramatically affects intelligibility of the received signal. The pre-emphasis network in the transmitter amplifies the higher-frequency content of the audio signal more than the lower frequencies. The de-emphasis network in the receiver compensates for this by reducing the gain of the higher-frequency audio signal thereby reducing (flattening) the frequency-modulated noise.

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