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Cardinal
What it is
Cardinal is a free, open-source modular synthesizer based on VCV Rack, available as a standalone app and an audio plugin. Its bundled build includes 1,382 modules from 84 authors or brands. It runs on Linux, macOS, Windows, and the web, with AudioUnit, CLAP, LV2, VST2, and VST3 plugin formats listed. Main, Synth, and FX plugin variants support MIDI input and output. Main has eight audio inputs and outputs and ten CV inputs and outputs, but is not available in AU or VST2 and is not yet available in CLAP. Mini offers a smaller, hand-picked module set, with two audio ports and five CV ports; it is available only as LV2 and standalone. Cardinal does not load external modules or connect to the official Rack library, and modules cannot be added to an existing build. OSC remote control works in the standalone app, not in plugin use. The project describes Cardinal as stable, while noting CLAP support is in progress and VST3 hosting inside Carla or Ildaeil is experimental. It is licensed under GPLv3+.
For and against
For
- Free and open source under GPLv3+.
- Includes 1,382 modules from 84 authors or brands.
- Main, Synth, and FX support MIDI input and output.
- Standalone OSC remote control is available.
- Runs on Linux, macOS, Windows, and the web.
Against
- External modules cannot be loaded or added.
- Main is unavailable in AU and VST2.
- CLAP support is still in progress.
- VST3 hosting inside Carla or Ildaeil is experimental.
The verdict
Cardinal offers a substantial built-in modular set in standalone and plugin forms, with MIDI support across its three main variants. Check the format and module limits first if you need external modules, Main in a particular format, or plugin-hosting features.
Who it suits
Cardinal suits musicians who want a free, open-source modular synthesizer as a standalone app or plugin. Those seeking a larger module collection or official support may prefer Rack Pro, which the maker identifies as an option for those needs.
Plans and prices
Cardinal
free/open-source · fixed built-in module set · no external module installation
Read 14 Oct 2026 · cardinal.kx.studio
Free
Fully free and open-source · Cardinal builds include built-in modules; adding modules to an existing build is not possible
Read 29 Sep 2026 · cardinal.kx.studio
On the record
- Build architectures
- Official releases include Linux armhf, arm64, i686, riscv64 and x86_64 builds plus universal Intel/ARM macOS and 32/64-bit Windows installers.github.com · read 14 Oct 2026
- Built-in modules
- The home page lists 1,382 included modules from 84 authors or brands.cardinal.kx.studio · read 29 Sep 2026
- Changelog event
- Cardinal 23.09 was released on 2023-09-17 and made OSC remote control an official feature.kx.studio · read 14 Oct 2026
- CV integration
- The LV2 implementation exposes real CV inputs and outputs for connecting to other modular systems.cardinal.kx.studio · read 14 Oct 2026
- Documentation depth
- The official site documents OSC activation, ports, message formats and headless configuration, while general usage relies heavily on VCV Rack documentation.cardinal.kx.studio · read 14 Oct 2026
- External modules
- Cardinal does not load external modules or connect to the official Rack library/store, and adding modules to a Cardinal build is not possible.cardinal.kx.studio · read 29 Sep 2026
- Included modules
- The project homepage reports 1,382 built-in modules from 84 authors or brands.cardinal.kx.studio · read 14 Oct 2026
- Installer security
- The macOS and Windows installers are unsigned and can trigger untrusted-developer warnings.github.com · read 14 Oct 2026
- Intended users
- The maker says Cardinal was created to provide Rack as a conventional open-source audio plugin and notes that Rack Pro may suit users seeking official support and its larger module collection.cardinal.kx.studio · read 29 Sep 2026
- Internal hosting
- Cardinal includes modules for hosting other plugins through Carla and Ildaeil.cardinal.kx.studio · read 14 Oct 2026
- License
- The Cardinal project is licensed under GPLv3 or later.cardinal.kx.studio · read 14 Oct 2026
- Limit: fixed configuration
- Synth and Software reported that users cannot add missing or paid VCV modules without modifying and compiling the source themselves.synthandsoftware.com · read 14 Oct 2026
- Limit: host compatibility
- Project release notes characterize Windows plugin behavior as problematic and Linux/X11 compatibility as dependent on the host DAW.kx.studio · read 14 Oct 2026
- Limit: standalone latency controls
- The same review found that standalone output-device selection was unavailable and changing the buffer setting did not audibly change latency.synthandsoftware.com · read 14 Oct 2026
- Limit: standalone Windows audio
- A reviewer reported clicking, crashes after sample-rate changes and unreliable audio-input behavior in the Windows standalone application.synthandsoftware.com · read 14 Oct 2026
- Main variant limits
- Main provides 8 audio inputs and outputs and 10 CV inputs and outputs; it is unavailable in AU and VST2, and the page says it is not yet available in CLAP.cardinal.kx.studio · read 29 Sep 2026
- Maker
- DISTRHO is an open-source cross-platform audio-plugin project led and primarily coded by Filipe Coelho (falkTX), under the KXStudio umbrella.distrho.kx.studio · read 14 Oct 2026
- Mini variant
- Mini is a reduced LV2 and standalone variant with a small module set, two audio ports and five CV ports.github.com · read 14 Oct 2026
