ABX Compressor Test is a research VST plug-in that implements 18 different compressor modes - that is 18 more or less significantly different algorithms. It was created to research how a good compressor should sound (and therefore how it must be designed).

All compressor designs are feed-forward and peak-detecting. The side-chain is always not filtered. The signal path is also unfiltered, that is it contains no sound enhancing of any kind (except for the gain adjustment performed by compression).

Different modes
The different modes comprise different envelope follower types, different transfer functions as well as different inter-operation between the internal parts of the compressor. The modes are numbered from 1 to 18, the literals in parenthesis hint at the difference and can be interpreted as follows:

• HQR = High quality transfer function (ratio).
• LQR = Low quality transfer function (ratio).
• S = Smooth operation (release).

Anyone is free to use and share this VST plug-in as long as they evaluate the different compressor modes to the best of their knowledge and report their findings and comments in this thread in the KVRAudio.com forum (where the plug-in is available for download).