Cardinal

Cardinal is a free, open-source modular synthesizer built on VCV Rack, offered as a standalone application and as a plugin. It is best for musicians who want a large ready-made module set in an audio workflow; its fixed contents make it a poor fit for anyone who depends on third-party modules.

Overview

Cardinal turns modular synthesis into a self-contained instrument, bundling 1,382 modules from 84 authors or brands. That gives newcomers and established patch builders a broad palette without requiring a separate module library. The trade-off is firm: Cardinal cannot load external modules, connect to the official Rack library or store, or accept additions to an existing build. It suits users content to work within the bundle, not those who want to assemble a continually changing collection.

Key features

Plugin formats and variants

The plugin is available in AudioUnit, CLAP, LV2, VST2 and VST3 formats. Main, Synth and FX variants all support MIDI input and output, which gives users several ways to fit Cardinal into a host-based workflow. Main has 8 audio inputs and outputs and 10 CV inputs and outputs, but it is unavailable in AU and VST2 and is not yet available in CLAP. That makes host and format choice consequential if Main’s routing is central to a setup.

Mini takes a different approach: it has a small hand-picked module selection, 2 audio ports and 5 CV ports, and is available only as LV2 or standalone. It may suit a compact installation, but users seeking the full bundled selection should consider the other variants.

Standalone control and privacy

The standalone application supports OSC remote control of patches and parameters; that control is not available in the plugin. The project says included modules are not allowed online access such as phone-home activity, and describes removing online access from the plugin and included modules. For users who want remote control, Cardinal therefore makes standalone the relevant choice.

Cardinal supports MPE and is described by its maker as stable. CLAP support remains a work in progress, while VST3 plugin hosting inside Carla or Ildaeil is experimental. Those caveats matter for users relying on either of those particular workflows. Cardinal is licensed under GPLv3+. Bug reports are directed to GitHub, and community discussion takes place in the #cardinal IRC room on Libera.Chat.

Pricing

Cardinal is fully free and open source: the Free plan costs nothing. It includes Cardinal’s built-in modules, with no added-module option for an existing build. There are no paid tiers to weigh against that bundle; the practical limit is the fixed module set, rather than a stated seat cap or usage quota.

Platforms

Cardinal is available on Linux, macOS, Windows and the web. It also has a standalone application, alongside the plugin formats described above. Variant availability is narrower than the overall platform list: Mini is LV2 and standalone only, while Main is unavailable in AU and VST2 and is not yet available in CLAP.

Who it's for

Cardinal is a strong fit for musicians who want a substantial modular environment at no cost, particularly those who value a conventional plugin as well as standalone use and can work with the included modules. It is less suitable for users who need the official Rack library, third-party module expansion, or OSC control while running the plugin. The maker points users seeking official support and a larger module collection toward Rack Pro.

Pros and cons

• Pros: 1,382 included modules from 84 authors or brands provide a broad starting collection without a fee.
• Pros: Standalone and five plugin formats give users multiple ways to use the modular engine, with MIDI input and output across Main, Synth and FX.
• Pros: MPE support and standalone OSC remote control add useful control options for compatible workflows.
• Cons: The module collection cannot be expanded, ruling out users who depend on external modules or the official Rack library.
• Cons: Main’s I/O capacity is not offered in AU or VST2, and Main is not yet available in CLAP.
• Cons: Mini’s smaller selection and LV2/standalone-only availability make it a narrower option rather than a general substitute.

Alternatives

For users who want a different kind of free or low-cost music tool, these options offer distinct trade-offs:

• VCV Rack is the direct alternative for users drawn to Rack’s ecosystem: its free Rack 2 plan is standalone, open source and includes free modules, while Cardinal deliberately excludes the official library and store.
• DefleMask may suit someone seeking a tracker-based music application instead; its full plan costs $14.99, paid once, while its free legacy version is 32-bit, unsupported and described as a demo.
• Sonic Pi is another free, open-source choice, developed by over 200 contributors since 2012, for readers who prefer that project to Cardinal’s modular synthesizer approach.
• Vital offers a free Basic plan with 75 presets, 25 wavetables and full synth features; pick it if that defined preset-and-wavetable synth package better suits your needs than modular patching.
• Dexed is free software under GPL v3 for readers considering a different free instrument.
• Helm is a pay-what-you-want standalone or plugin option for GNU/Linux, Mac OSX and Windows, including 32-bit and 64-bit versions.
• Surge XT is free and open-source under GPL3, and may suit users seeking a virtual instrument plugin on Windows, macOS or Linux.
• Synth1 is freeware in VSTi/AU plugin form for macOS and Windows.

Browse the Software Synthesizers directory for more options.

Verdict

Choose Cardinal if you want an extensive modular synthesizer in standalone and plugin forms without paying, and the included module set is enough for your work. The bundle’s breadth is its strongest reason to choose it; the inability to add modules is the clearest reason to look elsewhere, especially toward Rack Pro if official support and a larger collection matter.