Wow! This is one of the coolest pieces of software I've ever seen and its free! VCVRack is an open source modular synthesizer software platform developed by Andrew Belt that sounds great and is very intuitive and easy to install and use. The download is small and fast and the install is a breeze. This will run on macOS (all the way back to 10.7!) as well as Windows and Linux 64-bit. After downloading and installing this, I was digging in and making music in a matter of minutes and only had to reference the online manual once. VCVRack is the easiest to use and the most intuitive virtual modular synth software I've ever used. It's hard to believe that it's free, it feels like something that should cost several hundred dollars! The onscreen GUI is easy to use, just patch in modules with virtual patch cords and you're off and running. The system will only allow you to patch things that work together and as soon as you're near an input or output the virtual cables snap to their virtual jacks. I've used other commercial modular synth software and quickly been frustrated by the difficulty of the GUI in connecting the virtual patch cables. VCVRack has done a great job with their GUI. The virtual knobs and switches are also easy to manipulate. In general I'm not a big fan of using a mouse or trackpad to manipulate soft synths, but VCVRack is so easy to use and is so powerful right out of the gate, that I really had fun with it! The virtual rack itself, unlike real physical racks, just keeps growing horizontally and vertically as you add modules and scroll up/down and left/right. I wish I could make my real racks do this! There's no CPU meter, but the file sizes of the app and plug-ins are tiny and I got a few pretty big complex patches going on my 2012 Mac Book Pro running Mac OSX 10.8.5 with no glitches at all, and in all my use of VCVRack it never crashed once! I wish I could say the same thing about some commercial software I've bought.
At the time of this review, VCVRack is a standalone app so it won't work with your DAW, although this will likely change in the very near future. Because it's open source, there are a lot of third party developers and there is already an Ableton Link plug-in although I was not able to test it. VST/AU support is also planned with a VCV Bridge module coming soon, although this will be a cross application connection, not a plug-in within your DAW. There are also workarounds. Because VCVRack is modular, I was able to put two audio interfaces into my Rack and route one to my UA Apollo Twin and the other to my laptop's headphone jack and was then able to route audio from Pro Tools into VCVRack and back into Pro Tools. Its a bit tricky and easy to get feedback loops if you're not careful, but it otherwise worked fine and I was able to process tracks through the Mutable Instruments Clouds Module for instance. I had a little less luck with MIDI but I think if I had a multichannel MIDI interface I could have made it work, and I got some pretty crazy MIDI feedback loops going with my one channel interface!
The Clouds module is interesting to discuss for two reasons. One, like a lot of the popular Mutable modules (and a growing number of Eurorack modules in general), it's a DSP module and the code for it is open source, so the VCVRack version and the hardware version are running the exact same code. Besides the converter differences, the two modules are pretty close to identical. The other interesting thing about Clouds is that it was one of Mutable's best selling modules, but it's no longer in production, so if you missed out on it or can't find one used, VCVRack get's you pretty damn close for free. The cost of just the Mutable modules alone in VCVRack would be a few thousand dollars, so to be able to use the software versions with the exact same code for free is pretty great. I like that the modular synth community is very open and sharing in general, and it's nice to see guys like Olivier Gillet, Mutable Instruments principal developer willing to contribute to the VCVRack project.
The other great thing about this being open source is the already pretty big library of modules available that will only keep growing. For instance after using VCVRack for a little bit and getting a pretty complex patch going, I was a bit frustrated with being unable to pan anything and hitting limitations with mults as the only way to combine signals. I checked out the list of modules at www.switchedonrack.com/modules-monitor.html and found a free 8 channel mixer from Hora Music with pan and mute controls, and a few minutes later I was up and running with panning and better level controls. Hora Music also makes some larger mixers with Auxes and I ended up buying those for 15 Euros. I also found some cool modules from Vult, Gratrix, and Sonusmodular that I integrated into my rack.
Even if you're not interested in electronic music, keep in mind that you can easily run audio in to VCVRack and do lot's of creative processing with filters, delays, wave shapers, and grain delays and it's all modular, patchable and each patch can be easily saved.
If you read my review of Automatonism in Tape Op 121 but were maybe intimated by the underpinnings of that software in Pure Data, then you'll find VCVRack much more accessible. I think VCVRack is a great piece of software for anyone interested in audio processing or synthesis. Whether you're just learning and you're not sure where to start, or if you already have a bunch or hardware and software synths, beginners and seasoned synth nerds alike will find something to love about VCVRack.