An effect that allows the frequency-selective manipulation of a signal’s amplitude. The simplest equalizers are shelving types, offering the ability to cut or boost gain above or below a given frequency. Equalization doesn’t only change the level of specific parts of the audio spectrum, it also changes the phase of the affected frequencies relative to those that aren’t being EQ’d, i.e., EQ affects both the frequency response and phase relationships of the signal.
See composite equalization, pre-emphasis, room equalization.