InfernalSynth Is A FREE Semi-Modular Synthesizer


Sjoerd van Kreel releases InfernalSynth, a freeware semi-modular synthesizer VST3 plugin for Windows.

As a VCV Rack enthusiast, complicated synths are always exciting. There’s something about a slew of purpose-driven controls over every possible parameter that can inspire just as ably as the refined control set of the Roland Juno 106.

InfernalSynth falls firmly in the former’s camp, bringing together a variety of elements to give a deeply controllable synth with a lot of fun options.

InfernalSynth First Impressions

InfernalSynth’s interface comes across as a more sedate sibling to HrastProgrammer’s Tranzistow; there are a lot of controls present.

There are four oscillators to use with InfernalSynth, and they have a variety of modes for a good bit of diversity in sound generation.

Basic presents your bog standard waveforms. Mix can blend different waveforms, using standard analog waveforms to create more harmonically complex waves. DSF is an interesting one that uses distinct algorithms to make complex waveforms.

Oscillators can be tuned, synced, and have FM applied. So quite a few possibilities with just a single oscillator, let alone four of them.

Filtering is another subject entirely, with two distinct modes on offer. Users can select a state variable filter or a comb filter, and each has multiple variations for sculpting your sound around.

The signal path is wide open on InfernalSynth, and you can route audio anywhere you want between the four oscillators and twenty effects modules.

Effects are somewhat limited in scope, offering up filtering, reverb, delay, and a waveshaper. Having twenty slots allows for some creative design, however.

InfernalSynth TLDR And Specs

InfernalSynth is an impressively designed synth that is perhaps not for the faint of heart.

The core sound of the oscillators and filters is quite nice, and you have quite a bit of flexibility in how you approach designing a sound. You can also apply the intense effects sections and a plethora of modulators to other sounds, thanks to the inclusion of an FX version of the plugin.

This article only scratches the barest of surfaces of the possibilities of the synth.

InfernalSynth is, unfortunately, Windows-only and requires a 64-bit host. The only plugin format provided is VST3.

Download: InfernalSynth


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Liam is a producer, mixing engineer, and compressor aficionado. When not mixing, he can be found pretending to play guitar, as he has been doing for the last 20 years.


  1. Okaaaay… Let me first obtain a PhD in Applied InfernalSynthethics at Beelzebub University to give a final impression on what it is. In the meantime, it would benefit from a slightly bigger or resizable GUI, and for the love of anything that is unholy, a normal vertical mouse knob operation. The circular thing, ew… As for the square buttons, why aren’t they pentagrams is beyond me. >;-)
    Very interesting nonetheless, less scary than Transistow, somehow.

    • Being a lover of horror films, I think the GUI is interesting. Admittedly it’s cluttered and somewhat confusing on first glance, but the dark, creepy style of the design isn’t a turnoff for me.

    • Jeffrey Price


      I like simple. Complicated gives me a headache. When the GUI looks like the dashboard of a jumbo jet I’m out!!!

  2. The ugliest synth ever. Haven’t we had enough zombies/satanism/vampires/creepy/edgy stuff already in this world? Be good, make good things. Good as in kind, exciting, energising, moral.

    • Being a lover of horror films, I think the GUI is interesting. Admittedly it’s cluttered and somewhat confusing on first glance, but the dark, creepy style of the design isn’t a turnoff for me.

    • Goody two-shoes normies are such boring, joyless people. To call you “people” would even be an exaggeration

  3. Only 12 presets and unless I am missing something there’s no ability to save a patch? The circular knobs need fixing too. It would be great if those 3 things were addressed.

  4. Hey!

    Developer here. Thanks for the review! The thing’s got a mixed reception so far indeed mainly because of the UI. In fact, someone’s made a lovely alternate skin already, see here:

    On a more serious note, whatever you think of the plugin’s design (it was originally called SevenSynth, so themed as seven sins), the UI is indeed crowded. I think it could benefit from tabbed UI, maybe voice and global on separate screens, allow for bigger knobs, reduce (bot not replace) the bg images, etc. So I’m gonna ask you guys the same question as I did over at the audiosex forum, anyone interested in giving feedback occasionally as I re-do the UI layout?

    Also, couple of questions:

    @MRG really think the matrix routing is too complicated for a semi-modular (serious question)?
    @MRG, Chris: what’s up with the circular/vertical mouse thing? I certainly don’t hope you have to make an actual circular mouse movement in order to operate the knobs? If so, that’s a major bug.
    @Chris: only 12, yes. Might do more in the future but that’s it for now, I’d like to focus on the plugin itself. About the patch saving, I honestly thought that was host functionality. Is it common for hosts to not have a “save as preset” option?
    @Lawyer cake: ugly as in don’t like the design *at all* or just ugly as in don’t like the theme? Would you be more comfortable with it if I’d swap out the images for something more neutral, say, fluffy bunnies?

    Cheers!, Sjoerd

    • Fluffy bunnies… COVERED IN BLOOD! MWAHAHAHAHAH!! *cough*

      I mean, hi! >;-)
      – Too complicated? Oh, I dunno how to answer that, it is what it is. It’s fully featured, so it’s bound to have a lot of stuff on screen. Nothing inherently wrong about it. Let’s just say it demands a tad more thinking than a Juno-60 clone? It’s just a bit tiny for my screen/eyes combo and my mouse skills… :)
      – Yeah, major bug on my end then, circular movement of the mouse pointer to make the knobs move. No idea why. I’ll try it more later today… In the meantime, Win7 & REAPER 64bit, ‘Generic’ build, if that helps. I need to find another host to check. Mousewheel works, but in big steps tho. :/

      and while not directed at me :
      – VST3 patches are indeed supposed to be managed by the host. Some devs prefer to make their own format and manager to avoid problems with VST2/VST3/AU/FST/CLAP and various OS conflicts. I do believe some hosts had poor support for VST3 patches in the early days of the format, no idea if still the case.
      – We’ve had some people already expressing their uneasiness using plugins with an edgy vibe, certain words or images in these parts of the woods, for …reasons. It’s your baby, do what you think is right for you. It is open-source, I’m sure someone will make a lovely pink UnicornSynth theme/fork for it someday. ^_^;

      IIRC some DAWs on Windows don’t (didn’t?) really expect .vst3 folders but ‘compiled’ files. I wonder if some user troubles were about this. I believe it was because they don’t understand what some files are and choke on them.

      I wonder about having both knobs and numerical textboxes. A ‘better’ practice is to have bigger knobs and small value text under or in a separate ‘common place’ (think LCD display on old hardware). Or the newish kind of textboxes with a slider in them.
      That would allow to reclaim some, IMHO, wasted space to make things bigger, thus easier to access.

      Anyhow, interesting project, looking forward to what it’ll become. Thank you.

      • Hey!

        It appears VST3 supports both linear and circular knob modes, with an unclear default that is supposedly controllable by the host. So probably there’s an option somewhere in all hosts, but I’ve never seen it. Anyway I just decided to force linear mode in the code and put up v1.1.1 on the site. Hope that fixes your problem. About the patch loading, good to know, that puts it a bit lower on the to-do list. Probably still have to implement it myself eventually for hosts that don’t get this right.

        As for the UI, I’m not really concerned too much with the images right now. I thought it just was a fun theme but if it really turns out they are a major dealbreaker for a lot of people I can easily swap them out with anything else in a matter of hours. I’m trying to make a synth here, not offend anyone. Although i was a but surprised to see that anyone actually was.

        Your last remark’s absolutely spot-on! Can’t believe I didn’t think of that, just put up a single textbox somewhere that tracks the last-tweaked knob. Saves 33% screen space right there without having to give up exact-editing. Thanks a lot, greatly appreciated.

        -greets, Sjoerd

        • For the GUI, I was only giving examples, there’s also clean circular knobs with values in them.
          I guess my prefered is the Slider+Text-in-one combo, like in the graphical example I’ve given, as it is both instant visual -and- readable if needed/wanted.
          Feel free to experiment. :p

        • Ah-ah! Indeed, the linear/circular knob is a general option in the (some?) hosts.
          For anyone interested, in REAPER it is in Options menu, Preferences item, Plug-ins\VST, “Knob mode”. You need to close/reopen the plugin to take effect. \o/

  5. Sadly I can’t make this work in Cakewalk. Despite copying the InfernalSynth folder to common files\vst3 as instructed, CbB continually fails to load the VST. Interestingly, InfernalSynth does flash up briefly along with each of my other plugin folders as they are being scanned by the DAW but then, once all plugins have been scanned and loaded, InfernalSynth is stubbornly not in the list :-( I’ve checked the plugin manager for excluded plugins, but not there either. Real shame as this looks like it would be a great addition to my stable of synths. To Sjoerd, many thanks for all your hours & effort in developing InfernalSynth … just a shame that CbB won’t behave, or that I’m missing something obvious!

    • Hey!

      Does it just not load in Cakewalk or in all your hosts? If the latter, I fixed a couple bugs in V1.1.1 that might help you out. If the former, I now have a host-specific problem on my hands for a host I do not own :)

      -greets, Sjoerd

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