In the latter part of the 1980s, wide dynamic range compression (WDRC) amplification was introduced into the hearing aid market. Within a few years it was widely recognized as a fundamentally important new amplification strategy. Within 10 years nearly every hearing aid manufacturer had developed a WDRC product.

Compression is useful as a processing strategy because it compensates for the loss of cochlear outer hair cells, which compress the dynamic range of sound within the cochlea. Sensorineural hearing loss is characterized by loudness recruitment, which results from damage to the outer hair cells. WDRC compensates for this hair cell disorder, ideally restoring the limited dynamic range of the recruiting ear to that of the normal ear. This article reviews the history of loudness research, loudness recruitment, cochlear compression effects (such as the upward spread of masking) that result from and characterize OHC compression, and finally, outer hair cell physiology. The WDRC processing strategy is explained, and a short history of the development of WDRC hearing aids is provided.