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In telecommunication, preemphasis is a system process designed to increase, within a band of frequencies, 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 differences or saturation of recording media in subsequent parts of the system.

Preemphasis is commonly used in audio recording (Dolby B and C) and in FM radio transmission.

See also Federal Standard 1037C and MIL-STD-188.