Mastering

Amplitude Imposer

Amplitude Imposer is a free compressor VST plugin developed by ndc Plugs. Compatible OS(s): Windows, macOS.

Amplitude Imposer takes two stereo inputs, and imposes the amplitude envelope of the first one onto the second. It also has a feature where you can set a threshold level, and whenever the second signal’s amplitude falls below it, it is automatically amplified up to the threshold, in order to give a more constant signal to the amplitude imposer part.

It’s kind of like a compressor, but backwards.

http://www.niallmoody.com/ndcplugs

Advanced Clipper

Advanced Clipper is a free limiter and clipper VST plugin developed by Christian Budde. Compatible OS(s): Windows.

Advanced Clipper is basically a hard-clipping plugin with two stages. Additional oversampling reduces alias noise. The oversampling algorithm is based on butterworth filters (as can be found in rubberfilter) and thus will affect the group delay (you can notice a delay of some samples in extreme cases).

Features:

Two stages of minimum phase, butterworth oversampler.

Hard clip at higher sample rates.

Oversampling of up to 16x (in both stages).

Filter order up to 64 (using the max. order will introduce noticeable group delay).

Tunable transition frequency (in parameter view).

http://www.pcjv.de/

ABX Compressor Test VST

ABX Compressor Test VST is a free compressor VST plugin developed by Michael Gruhn Audio. Compatible OS(s): Windows.

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).

http://audio.michael-gruhn.com/