Viper aims to deliver the sound characteristics of legendary hardware synthesizers in a virtual format. We can call Viper a Virtual Performance synth, with a vast array of features like: multiple oscillator types with user waveforms, Sync, Frequency Modulation, Ring Modulation, unison up to 8 voices, filter saturation, filter routings, mod matrix, high quality effects, a powerful arpeggiator, and much more!

A lot of time and research has been invested to make the sound engine of Viper capable of delivering a wide array of sounds, everything from smooth, lush pads, huge basses, and powerful leads, typically associated with traditional analog synthesizers. This was achieved with careful coding, experimenting, analysing hardware synths, and using the ear to fine tune the controls. A constant randomization is also active in the synth to slightly alter its sound to mimic electronic components.

The engine is written in optimised code to use as little CPU consumption as possible, while maintaining a high quality sound engine, finding a good balance between the two. The synth automatically turns off any parts that are not used to further reduce CPU usage. Viper also has a smoothing algorithm for its controls to remove the ‘steppyness’ when it goes between values to give that extra polished sound.

Key features:
● Classic Oscillators with user waveforms
● Multisaw (up to 9x Sawtooth waveform)
● Sub Oscillator
● Noise with coloring
● Punch
● Osc Sync, FM, RM
● Unison up to 8 voices
● 2 Zero Delay Feedback filters with Low Pass, High Pass, Band Pass, Band Reject (notch)
● Filter Saturation curves
● 4 Filter routings: Serial 4, Serial 6, Parallel, Split
● 4 Envelopes: Filter Env, Amp Env, Mod 3 and Mod 4
● 3 LFOs with Oscillator shape morphing
● Mod Matrix
● FX:
● Character (analog boost)
● Distortion
● Filter effects: Ring Modulator, Frequency Shifter, Vowel Filter, Comb Filter
● Phaser
● Chorus
● Delay
● Reverb
● Equalizer
● Arpeggiator with user patterns and Midi Out
● Built in Preset browser
● Section locking
● Midi learn
● Resizable GUI


Download demo version:
Demo restrictions: Preset saving is disabled, silence every 60 seconds. (Because of the demo limitations, automation is not available in some hosts, but is fully functional in the retail version)
Requirements: Win 32/64 compatible system with SSE2 (or higher).

User Manual:
The user manual for Viper can be downloaded from here: Viper Manual.pdf

This is a 32 & 64-bit VST for Windows only! All future updates are free!
Please evaluate the demo thoroughly before purchasing!

Why no Mac version?
Unfortunately, FlowStone does not yet support export to AU, Mac VST yet. As soon as FlowStone supports this, the synth will be available in this format.

Free Soundbanks:
Daniel Craighead Trance Access for Viper Vol.1.zip


  • humphrey
    Jun 03, 2018

    @Lukas: if you have a look at the JP6K site Adam clearly stated:
    „64-bit version?
    The 64-bit version of the VST for Windows is in planning stage, and will arrive in the near future, as a free update to all customers.“

  • Trictonez
    Jun 03, 2018

    Hi, I bought the plugin some time ago, and I would like the 64 bit version as it is released now but can’t really find a way to get the download. So would love some help with this.

    • Adam Szabo
      Jun 03, 2018

      Hi, I sent out the newsletter with the info on how to download it. Just use the same link as the original download that you got in the receipt with your serial.

  • Richard
    Jun 04, 2018

    This thing sounds awesome. Great Job!
    Really hope to see a mac version of this plugin 🙂
    Let’s hope FlowStone makes it mac compatible

  • Chris
    Jun 04, 2018

    Just bought the 64. Loads up OK in Studio One 4. SO far so good.

  • TCommando
    Jun 04, 2018


    Why you dont have monthly payment system like Lennar Digital have? Its really nice way to pay. 🙂

    I think that every bigger music software developers should have this system because this software is really expensive. 🙂

    • Adam Szabo
      Jun 04, 2018

      Because they probably send you some custom c++ code that you have to write in the synth and Viper is written in assembler, its not possible.

  • Ari Linker
    Jun 04, 2018

    Most of the producers i know uses Mac, you are missing a big piece of the cake..

    • Adam Szabo
      Jun 04, 2018

      I wish I could make it for Linux, Android, iOS, Mac, but its not possible at the moment, Ive written on my site the reasons.

  • Kjell
    Jun 11, 2018

    Just tried the 64-bit demo for Windows. I run Ableton live 10 on WIN 10, and live just crashes if I try to load it into a project. When I try it in an empty project, it crashes live after a few minutes.

  • Jacob
    Jun 11, 2018

    I just want to say that I have owned two Virus TIs since 2006. In my experience, there is no other softsynth that comes close to Viper in nailing the Virus sound. Without devolving into subjective expressions like “better” or “fatter” it is fair to say that the Virus has a very unique sound that none of the other major softsynths quite capture. I have seen various explanations for the Virus’ sound from the DACs to “magic pixie dust.” While Viper doesn’t have the converters, it has the pixie dust in spades and I cannot thank the dev enough for making such an incredible emulation!!!

    • Pascal Gregory
      Jun 11, 2018


    • Yasu
      Jun 15, 2018

      Reveal cant even come close to Viper. the Virus unique sound is what you paid for and Viper have it for a fraction of cost.

  • Adrian
    Jun 13, 2018

    now extend the JPK and you will be a legend!

  • Vertex Helix
    Jun 24, 2018

    Virus owner here and YES, this is the SHIT! Kudos to Adam for all the time he invested. Well worth it

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Dec 16, 2019

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