What is an Expander?

An expander is an audio processing tool used in recording and mixing to increase the dynamic range of an audio signal. It works by reducing the volume of sounds that fall below a certain threshold, making quiet sounds quieter while leaving louder sounds mostly unaffected.

An expander operates in the opposite way of a compressor. While compression reduces the difference between loud and quiet sounds, expansion increases that difference. When the signal drops below the set threshold, the expander gradually lowers its level according to a selected ratio, helping reduce background noise and unwanted low-level sounds.

Expanders are often used on vocals, drums, and instrument recordings to clean up quiet noise between phrases or hits. A noise gate can be considered an extreme form of expansion, where the audio is reduced almost completely once it falls below the threshold.