Concrete FX synths are something of hidden juwels. Always cheap, powerfull, innovative and unique sounding, they seem to pass the mainstream of Vsti curiosity. Viper is no exception, unfortunatly, despite one of the most unique sounding synths i know of, it doesn´t get much recognition. What a shame ! Why?

To begin with, Viper is extremly complex, cheap, and easy to programm. The GUI is visually appealing and well designed, and is - with the one-page-design - intuitive. There are options en masse; from around 100 resynthesized waveforms, 4 Oscillators with fm, sync and filter bus routing to chose, to 2 filters with exoctic types like comb or formant filter, several LFOs, envelopes, an arp/ step sequencer, (not) ending with a modulation matrix, good effects, portamento and legato options, and midi learn. Like all CFX synths, it is really a semi-modular synth; but unlike some of the more early ones, it has a finished, polished feel to it.
This extend to the sound, of course. Like all CFX synths, Viper sounds basically warm, with some machinesque spark to it (hard to describe).With 4 OSCs and mainly digital sonic outlook, it has something of the tone of huge 80ies synths, maybe a cleaner Version of the PPG, but - and here comes its name in - differs in sounding dry, sometimes biting, and very organic. It can do nearly everything soundwise, deep basses, great athmospheric pads, machine fx, leads, organs, but excels at reed-ish, brassy and even guitar-like feedback sounds. Whats so great about Viper is the way it moves itself in the mix; even overbearing sounds blend in nicely. Also, it is immensely playable, its organic, moving timbres allow really expressive and immersing playing - really a musicians synth.

What else ? Documentation is too technical, though complete, presets are great, price is too low (feature-and soundwise, its rather in the 100-200 € category), support is outstanding.
Give it a try ! Very recommended.