VCV Rack is a free (open source) virtual modular synthesizer available as a standalone application (VST/AU plugin version coming soon!) for Windows, macOS, and Linux.
Described by its developers as an “open source virtual Eurorack DAW”, VCV Rack is currently the closest one can get to using a hardware modular synthesizer without spending any money (apart from investing in a computer in the first place). There are more than a few free modular synthesizer plugins out there (such as the recently released Fathom Mono), but none of them capture the workflow and the experience of using a hardware modular synth as closely as VCV Rack does.
Downloading and installing VCV Rack could hardly be any easier. Visit the project page linked at the bottom of this article, download the version of the application that is compatible with your OS, extract the downloaded archive and you’re good to go! The initial setup is equally fast since your computer’s MIDI and Audio interfaces are presented as modules that should be placed in the virtual rack. There’s no menu diving to worry about here. Better yet, if you own a multi-out audio interface and some hardware modules (or other compatible hardware such as the Arturia Microbrute) you can send the signal directly from your audio interface to the hardware instrument and vice versa. A soon to be released CV Interface extension for VCV Rack will ensure compatibility with CV-MIDI-CV interface modules.
Moving on to GUI design, VCV Rack looks modern, clean, and polished. Virtual modular synthesizer UIs can quickly turn into a complete visual mess due to all the virtual patch cables hanging around everywhere, but I didn’t run into such issues while testing VCV rack. The color scheme is contrasted enough to make the visual elements stand out, yet subtle enough to prevent distraction and visual overload. The cable tension slider on the top panel is used to control the length of the virtual cables if things become a bit cluttered. The different modules are nicely designed, with a subtle cell-shaded look which works great in this context. Overall, the GUI design is both visually pleasing and user-friendly.
As for the sound, VCV Rack isn’t a mind-blowingly detailed emulation of analog hardware. The sound of its individual components like oscillators and filters won’t blow you away but is certainly adequate for today’s standards. In other words, VCV Rack doesn’t attempt to deliver the sound quality of, say, U-He DIVA. And that’s to be expected due to the complexity of modular synthesizers and the potential CPU strain that would come as the result of increased audio quality. However, none of the components sound bad, and the sound is on par with the majority of virtual synthesizers nowadays. Speaking of CPU usage, though, I’d like to see a performance monitor added in a future update, to let the users know how much processing firepower they have left while building a patch.
VCV Rack is currently on offer as a standalone application only. However, word from the developers is that users will soon be able to connect VCV Rack to their digital audio workstation of choice with the forthcoming Rack Bridge VST/AU plugin add-on. This will instantly make VCV Rack the single best free modular synthesizer VST/AU plugin on the market. If you’d like to add a bit of modular synthesis power to your DAW in the meanwhile, though, take a look at the Softube Modular ($89) virtual instrument.
Perhaps the best thing about VCV Rack, though, is the fact that it’s open source. This allows anyone interested (and with some coding knowledge) to develop additional modules for VCV Rack, just like manufacturers can build Eurorack modules.
First off, you can expend the essential set of modules that come with the basic version of VCV Rack by registering for a free user account at VCV (only an email is required) and clicking the “Add” button next to the modules listed on the main project page. These will be added to your user account and downloaded automatically when you hit the “Refresh Modules” button in VCV Rack. At the moment, there’s already a great selection of additional “official” modules to choose from, including add-ons based on Mutable Instruments Eurorack modules, the Synthesis Technology E340 Cloud Generator, and various Befaco modules. It seems like more modules will be added to the project page soon.
But it gets better. Autodafe has already created a bunch of freely downloadable modules for VCV Rack, which you can download right now from their website. With this first set of Autodafe modules, you’re getting an LFO (hooray for that!), a couple of step sequencers, a clock divider, a fixed filter bank, a bitcrusher, and a distortion module. More modules are in the works and expected for release very soon, including a drum module which you can preview in the video above. Exciting times for modular synth fans!
VCV Rack is available for free download via VCV (10.5 MB download size, ZIP archive, standalone application for Windows, macOS, Linux).