What it does
Audio dynamic range expander.
The expander increases the dynamic range of the audio signal by reducing the low amplitudes even lower (thus "expanding" the dynamic range between the low and high components). The user defines the threshold below which the expansion should be applied. The expander, which is essentially the opposite of a compressor, works by measuring the average signal power and applying a logarithmic automatic gain control to the signal, based on the average measurement.
In this example, the drums are expanded such that the usually low-volume contributions (e.g. the trailing cymbal echos) are further supressed. (Compare with the original sound by momentarily connecting the input file directly to the output device.)