Companding noise reduction works by first sending the source matrial through a compressor, thus compressing the source material’s dynamic range (in this case by a factor of 2) before being recorded to a medium known for noise such as magnetic recording tape. The compressed audio becomes contaminated with noise, but is passed through an expander during playback, and the noise from the recording medium is masked by expansion of the dynamics. This results in a reduction of perceived noise. See also dbx™ noise reduction.