Definitions for "Preemphasis"
It is a process to increase the amplitude of a certain frequency relative to other in a signal, to help them to override noise. It is complemented by deemphasis before final reproduction of the signal is received.
In processing electronic audio signals preemphasis refers to 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. That is the mirror of the deemphasis. The whole system is called emphasis.