Quoting from a thread from a few days ago - key point seems to be PSP's version is indeed more "rougher" than other vca clones, by which i take to mean coloured.... in case useful http://www.gearslutz.com/board/new-p...-plugin-6.html
Email from PSP:
After releasing the PSP BussPressor we became aware that there is some confusion regarding the differences between our various dynamics processor plug-ins. In this short email we would like to explain the main differences.
All of PSP dynamic processors are based on unique algorithms. They do not share characteristics except for the FAT double sampling used in the PSP VintageWarmer and the PSP MasterComp. Each PSP compressor/limiter plug-in represents a different approach to dynamic processing. The PSP BussPressor
is based on the character of the SSL BusCompressor but we tuned our plug-in to be slightly rougher when compared to some other VCA plug-in clones.
In our opinion when used aggressively the PSP BussPressor is highly suitable for rock music. In the Auto mode the character changes and the plug-in can be used to add a smooth "gluing" effect. Another benefit of the BussPressor is its parallel compression mode but don't forget it also offers a high pass side chain filter useful for reducing kick drum pumping and an adjustable Auto release mode.
The PSP oldTimer is a bit "pillowish" compared to the PSP BussPressor. Although it will not provide the roughness of the PSP BussPressor it is a very versatile compressor, suitable for individual tracks, groups and master busses. It distinctly glues the audio together whenever used and it sounds especially good with (but is not limited to in any way) all acoustic instruments, vocals and entire recordings including jazz and even classical music. PSP oldTImer can be very useful on main tracks in the Mix and whenever a sweet polishing might do the job.
The PSP MasterComp is a compressor designed with transparency in mind. We mainly focused on low distortion when designing the algorithm and then we added special features to control the stereophony and channel linking. The result is a very smooth response suitable for all situations when coloration is not desired.
The PSP MixPressor (included in the PSP MixPack bundle) is a basic compressor created with track processing in mind but also able to process a group. Even though the PSP MixPressor algorithm is simple compared to our other compressors it still offers plenty of controls which combined with its range of compression curves make this plug-in unique and versatile.
The PSP VintageWarmer is a kind of special brick wall limiter plug-in. Although it can be set for a long release time its response is always usual for limiters. The only way to get transients thru is to use Warmer's Mix feature to get parallel processing. Using the knee and timing settings carefully a nice density can be achieved from a track.