The Complete Handbook of Equalizers

Chapter 1: Understanding Equalizers

What Equalizers Actually Do

An equalizer is a tool that changes the relative loudness of different frequencies in an audio signal. That definition is accurate but useless without context. In practice, an equalizer lets you boost or cut specific frequency ranges so that a recording, performance, or installed system sounds the way you want it to. It is one of the most widely used signal processors in audio, appearing in studio mixing consoles, live sound reinforcement systems, broadcast equipment, home theater setups, car audio, and anywhere else that audio needs adjustment.

The reason equalizers are everywhere is simple: real-world audio rarely sounds right without them. A vocalist recorded in a bedroom has too much low-end rumble and not enough clarity. A live sound system in a gymnasium resonates badly at 250 Hz. A mastering engineer needs to reduce harshness in vocal recordings. A hearing-impaired listener wants to boost high frequencies they can no longer hear naturally. In every case, the equalizer solves a problem that either exists in the source material or emerges from the environment and equipment.

To understand why, it helps to know what frequencies are. Sound is made of waves, and the frequency of a wave determines its pitch—how high or low we perceive it to be. Humans hear frequencies ranging from about 20 Hz (very low bass) to 20,000 Hz (very high treble), though the range is narrower in children and most adults. An equalizer divides this range into sections and lets