equalisation

Equalisation, or equalization in American spelling, is the process of adjusting the balance between frequency components within a signal to achieve a desired tonal character or to compensate for system response. In audio, this typically involves boosting or cutting specific frequency ranges. In telecommunications and signal processing, equalisation refers to applying filters to counter distortion introduced by a channel, such as intersymbol interference.

In audio engineering, common tools are graphic equalizers with fixed frequency bands, parametric equalizers with adjustable center frequency, gain and Q factor, and shelving filters that affect all frequencies above or below a crossover point. High-pass and low-pass filters remove unwanted low or high frequencies. Equalisers are used during mixing to shape tone, during recording to compensate microphone or room response, and during mastering to achieve a balanced overall sound. They can be hardware units or software plug-ins.

In digital communications and signal processing, equalisation may be adaptive, changing filter parameters in response to the channel. Such adaptive equalizers aim to reverse channel-induced effects to improve data recovery. Common applications include modem, wireless, and broadband systems where the transmission path changes over time.

Good practice emphasizes gradual adjustments, minimal boosting, awareness of phase shift and naturalness of sound, and consideration of the overall mix. The term is used across audio, broadcast, and data communications.