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


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  • Nico Østergaard
    Aug 04, 2018

    After a little week of using it “Demo and paid version” i gotta say it could be my new powerhouse VST next to my TI2 desktop.

    However, I got a few suggestions for future development:
    1. Faster LFO rate.
    – 43.0 Hz is too slow, compared to what Serum and Spire can do. Also, add more waveforms to the LFO section? Perhaps something FM related. User waveforms would benefit a lot for Viper too in this case.
    2. Add a parameter for the Pitchbend.
    – Routing Osc Pitch 1, 2 and 3 in the matrix to be controlled by an LFO isn’t a stable workflow. having a pitch bend parameter for the plug-in would be ace, give you more room to do crazy routings too.

    The LFO is kinda what is holding me back a bit from using it extensively, otherwise, I would’ve replaced any soft VST with it.
    Quality wise it is insane but I am fairly sure that these upgrades would draw in some serious attention too.

    Anyhow, fantastic work and great resemblance of the TI platform can’t wait to see what ideas you have for it 🙂

    • Adam Szabo
      Aug 04, 2018

      Thank you for the suggestions. I dont know if you noticed, but Viper already has a Pitch Bend called the “P Bend” knob on top. You can also control other parameters with it from the matrix.

      • Nico Østergaard
        Aug 04, 2018

        Anytime, I’m seriously amazed, cannot even fathom how many hours you might’ve spent on this already. I find it revolutionary how we can compete against popular VA’s like the TI platform, regardless of its age. 🙂

        About that P Bend:
        I noticed it, but I want to control the Pitchbend inside the plugin through its LFO’s, or just the Matrix. I personally would find that quicker to work with because if I was to fill up 1 Matrix slot with Osc pitch 1, 2 and 3 to be controlled by 1 LFO source, I would have to create a 2nd slot for the same source which I kinda want to avoid for messy workflow. This is just an idea though.

        My first initial thought was just the LFO rate should be faster “100hz or faster maybe”, and the amount of LFO waveforms could be increased. Perhaps you can implement the osc waveforms in this case? At least the FM ones as I fail to see what else would be usable in the LFO, they are perfect for creating sick lead layers.

        I hope this was useful, it is quite a mouthful even though it is such a small thing 😛

        • Adam Szabo
          Aug 04, 2018

          I still dont really understand what you would like to do with the pitch bend. You can try to link the LFO to the “Transpose” and it moves the pitch of all oscs and it will only use one slot, or you dont even need the mod matrix because you can assign a separate one on the LFO page.

          • Nico Østergaard
            Aug 18, 2018

            Sorry that I didn’t reply since last time!

            I didn’t know that “Transpose” could do this… My pitchbend issue has been resolved then, i just need more time with the plugin all along. Sorry for the confusion 😀

            Anyhow i just discovered a minor bug, when using FL 20, some parameters reset themselfes by either cloning one instance of Viper, or reloading the project.. Mainly in the LFO section, i noticed that my assignments to OSC1 and 2’s pitch in LFO1 just goes back to 0. Has anyone reported this to you before?

    • Lorenzo
      Sep 12, 2018

      I have to agree with Nico, the maximum LFO rate is very slow compared to other plugins.

  • Jack Cimino
    Aug 17, 2018

    This sounds cool, but I think the anti-aliasing filter is too soft. Besides the bit reducer effect, can you add an option to disable anti-aliasing?

  • Rubén Aragoneses
    Aug 23, 2018

    Hey Adam, I have a problem with Viper when it comes to saving presets. I’ve notice that when I make a preset and I save it, when I load that preset later on, the LFO modulation 1 parameter it is at 0 instead that the value I gave it while making the preset. It is so frustrating because no matter how many times I do it, it will never save its value, any help?

    Thank you very much

    • Adam Szabo
      Aug 23, 2018

      Yes its an issue I am looking into it

  • Nick Stalhood
    Sep 08, 2018

    Add sine wav to sub osc would be a big improvement in that section

  • Bizzyworks
    Sep 09, 2018

    Great sounding synth Adam. Any chance you could make it available as an fx Plugin to use just the fx of Viper? I’d love to put that reverb on a separate channel. 😉

    • Adam Szabo
      Sep 09, 2018

      Thanks, Im glad you like the synth! I am not sure about a full fx plugin, but I might release the reverb as a free plugin later in the future 😉

  • Tvbal
    Sep 13, 2018

    Really impressed by the demo! Just wondering, how many license uses would I get if I buy it? Can I use it on my desktop and laptop?

    • Adam Szabo
      Sep 13, 2018

      Im glad you like the demo! Yes you may install it on both your computers.

  • Dalil
    Sep 15, 2018

    Will there ever be the possibility to import Virus sounds into Viper? Do you plan any discounts for example on black Friday?

    • Adam Szabo
      Sep 15, 2018

      I am not sure if it will be possible to import Virus soundbanks in the future, but never say never. I dont know about discounts yet, but there is a possibility yes.

  • MatkatMusic
    Sep 16, 2018

    1st Q) Is there a particular reason you are not using the JUCE framework to develop your plugins? You’d be able to compile for AU, VST2, VST3, AAX for both Windows, OSX, and AUv3 for iOS. It’s the most used framework for audio plugin development these days. lots of big companies (presonus, Universal Audio) use it for their plugins and GUIs. JUCE did the hard work when it comes to DAW compatibility.
    2nd Q) Was this modeled after a TI2 or an earlier Virus?

    • Adam Szabo
      Sep 16, 2018

      Unfortunately I dont know C++ which you need for JUICE. It would take me years to learn it and I dont have that time.
      Viper is inspired by the TI, it does things the Virus cant do, and the Virus does a few things Viper cant do (yet 🙂 )

  • Benedetto Schiavone
    Sep 17, 2018

    News about wavetables support?

    • Adam Szabo
      Sep 17, 2018

      It will come in the not too distant future.

  • ProgHouse065Music
    Sep 29, 2018

    Any new soundsets is in the planning for Viper. There only one official I think until now. This is something that make a difference too. Maybe you could give Viper to some sound engineer like Aiyn Zahev to get some new soundsets.

    • Adam Szabo
      Sep 29, 2018

      Yes there are lots of soundsets planned for the future!

      • Ronald
        Sep 29, 2018

        Great! I hope for a sound bank in Tangerine
        Dream and cinematic said tyle. I don’t need more EDM style
        sounds. 🙂

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