, a 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.
Note: Preemphasis has applications, for example, in audio recording and FM transmission.
Source: from Federal Standard 1037C and from MIL-STD-188
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