What it does
Audio dynamic range compressor.
The compressor reduces the dynamic range of the audio signal by "compressing" the high amplitudes downwards. The user defines the threshold above which the compression should be applied. The 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 massively compressed such that the usually low-volume contributions (e.g. the kick drum) are over-emphasised. (Compare with the original sound by momentarily connecting the input file directly to the output device.)