Meaning of preemphasis

pre•em•pha•sis

Pronunciation: (prē-em'fu-sis), [key]
— n. Electronics.
  1. a process of increasing the amplitude of certain frequencies relative to others in a signal in order to help them override noise, complemented by deemphasis before final reproduction of the signal being received.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.