Neural provides its "Codec Pre-Conditioner" in at least two types of devices, a "NeuStar UltraLink digital radio audio conditioner" built as a physical device and a "Neustar SW4.0" built as a piece of software on Windows XP.
Manual of the software indicates that the pre-conditioner works by analyzing noise in each frequency bin and masking them to not exceed predefined limits, so that they would not overwhelm a codec.