compression
An audio effect that reduces the dynamic range of a signal by attenuating loud parts and boosting quiet parts.
In Depth
Compressors automatically control volume by reducing the level of signals that exceed a set threshold. This evens out dynamics, adds sustain to guitars, controls vocal levels, and glues mixes together. In country guitar, compression creates the characteristic clean sparkle. In funk bass, it adds snap and consistency. In mastering, it ensures consistent loudness across an album. Over-compression has become controversial in the loudness war era.
The loudness war, driven by excessive compression in mastering, led Metallica's Death Magnetic album to be so compressed that fans preferred the Guitar Hero video game version.