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Cardinal

cardinal.kx.studio

Free plan Open source WebWindowsmacOSLinuxAPISelf-hosted
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Spec score 9.0 #2 of 38 in Software Synthesizers

What it is

Cardinal is a free, open-source modular synthesizer based on VCV Rack, available as a standalone app and as a plugin. It bundles 1,382 modules from 84 authors or brands, but does not load external modules or connect to the official Rack library or store; modules cannot be added to an existing build. Cardinal runs on Linux, macOS, Windows, and the web. Its plugin formats are AudioUnit, CLAP, LV2, VST2, and VST3, with Main, Synth, and FX variants that all support MIDI input and output. Main provides eight audio inputs and outputs and ten CV inputs and outputs, but is unavailable in AU and VST2 and is not yet available in CLAP. Mini has a smaller hand-picked module selection, two audio ports, and five CV ports, and is available only as LV2 or standalone. OSC remote control works in standalone use, not in the plugin. The project describes Cardinal as stable, while noting CLAP support is still in progress and VST3 hosting inside Carla or Ildaeil is experimental. It is licensed under GPLv3+.

Spec sheet

What it does
Cardinal is a virtual modular synthesizer based on VCV Rack, delivered as plugins and a standalone application.Read 14 Oct 2026 · cardinal.kx.studio
Product
Cardinal is a free, open-source virtual modular synthesizer based on VCV Rack and packaged as a self-contained plugin and standalone app.Read 29 Sep 2026 · cardinal.kx.studio
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.Read 29 Sep 2026 · cardinal.kx.studio
Support
The maker asks users to report bugs on GitHub and lists the #cardinal IRC room on Libera.Chat for community discussion.Read 29 Sep 2026 · cardinal.kx.studio
License
The Cardinal project is licensed under GPLv3 or later.Read 14 Oct 2026 · cardinal.kx.studio
Maker
DISTRHO is an open-source cross-platform audio-plugin project led and primarily coded by Filipe Coelho (falkTX), under the KXStudio umbrella.Read 14 Oct 2026 · distrho.kx.studio
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.Read 14 Oct 2026 · github.com
Built-in modules
The home page lists 1,382 included modules from 84 authors or brands.Read 29 Sep 2026 · cardinal.kx.studio
Changelog event
Cardinal 23.09 was released on 2023-09-17 and made OSC remote control an official feature.Read 14 Oct 2026 · kx.studio
CV integration
The LV2 implementation exposes real CV inputs and outputs for connecting to other modular systems.Read 14 Oct 2026 · cardinal.kx.studio
Documentation depth
The official site documents OSC activation, ports, message formats and headless configuration, while general usage relies heavily on VCV Rack documentation.Read 14 Oct 2026 · cardinal.kx.studio
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.Read 29 Sep 2026 · cardinal.kx.studio
Included modules
The project homepage reports 1,382 built-in modules from 84 authors or brands.Read 14 Oct 2026 · cardinal.kx.studio
Installer security
The macOS and Windows installers are unsigned and can trigger untrusted-developer warnings.Read 14 Oct 2026 · github.com
Internal hosting
Cardinal includes modules for hosting other plugins through Carla and Ildaeil.Read 14 Oct 2026 · cardinal.kx.studio
Limit: fixed configuration
Synth and Software reported that users cannot add missing or paid VCV modules without modifying and compiling the source themselves.Read 14 Oct 2026 · synthandsoftware.com
Limit: host compatibility
Project release notes characterize Windows plugin behavior as problematic and Linux/X11 compatibility as dependent on the host DAW.Read 14 Oct 2026 · kx.studio
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.Read 14 Oct 2026 · synthandsoftware.com
Limit: standalone Windows audio
A reviewer reported clicking, crashes after sample-rate changes and unreliable audio-input behavior in the Windows standalone application.Read 14 Oct 2026 · synthandsoftware.com
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.Read 29 Sep 2026 · cardinal.kx.studio
Mini variant
Mini is a reduced LV2 and standalone variant with a small module set, two audio ports and five CV ports.Read 14 Oct 2026 · github.com
Module extensibility
Users cannot install new modules into an existing build; additional open-source modules must be integrated at build time.Read 14 Oct 2026 · cardinal.kx.studio
Module licensing rule
Included modules must use licenses compatible with GPLv3+; GPLv3-only modules are excluded.Read 14 Oct 2026 · cardinal.kx.studio
OSC API
Standalone Cardinal supports OSC remote control of patches and parameters from version 23.09 onward.Read 14 Oct 2026 · cardinal.kx.studio
OSC defaults
The OSC server defaults to port 2228 and headless builds can select another port with CARDINAL_REMOTE_HOST_PORT.Read 14 Oct 2026 · cardinal.kx.studio
OSC limitations
OSC control is unavailable when Cardinal runs as a plugin, and parameter discovery is still undocumented for one message type.Read 14 Oct 2026 · cardinal.kx.studio
OSC remote control
OSC can remotely control patches and parameters in standalone Cardinal, but is not available when Cardinal is used as a plugin.Read 29 Sep 2026 · cardinal.kx.studio
Plugin formats
Official builds provide AudioUnit, CLAP, LV2, VST2 and VST3 formats.Read 14 Oct 2026 · cardinal.kx.studio
Plugin variants
Main, Synth and FX variants share the same processing but differ in metadata and input/output layouts.Read 14 Oct 2026 · github.com
Praise: accessibility
Bedroom Producers Blog praised Cardinal as a free way for beginners to learn modular synthesis and highlighted quick module search and three equal-performance variants.Read 14 Oct 2026 · bedroomproducersblog.com
Praise: G2 reviewer
The lone G2 reviewer praised easy access to difficult legacy databases but cited a limited product range and computer-compatibility problems.Read 14 Oct 2026 · g2.com
Praise: module collection
Synth and Software described the bundled collection as a powerful one-stop package with more than 1,200 modules and highlighted the Valley Plateau reverb.Read 14 Oct 2026 · synthandsoftware.com
Praise: value and sound options
Bonedo praised its free plugin availability, large module selection, VCV-like operation and broad sound-design possibilities.Read 14 Oct 2026 · bonedo.de
Rating on G2
4.5 out of 5 from 1 reviewRead 14 Oct 2026 · g2.com
Rating on GetApp
0 out of 5 from 0 reviewsRead 14 Oct 2026 · getapp.com
Security and privacy
The project says online access such as phone-home is not allowed for included modules and describes removing online access from the plugin and included modules.Read 29 Sep 2026 · cardinal.kx.studio
Self-contained design
Cardinal packages its modules in one binary and does not connect to the official Rack library or store.Read 14 Oct 2026 · cardinal.kx.studio
Stability
The about page describes Cardinal as stable, while noting that CLAP support is a work in progress and VST3 plugin hosting inside Carla or Ildaeil is experimental.Read 29 Sep 2026 · cardinal.kx.studio
Standalone systems
Standalone versions are offered for FreeBSD, Linux, macOS, Windows and the Web.Read 14 Oct 2026 · cardinal.kx.studio
Support channel
Development support is provided through GitHub issues and the #cardinal IRC channel on Libera.Chat.Read 14 Oct 2026 · cardinal.kx.studio
Web deployment
The WebAssembly version can be self-hosted as static files and stores patches and settings in browser storage.Read 14 Oct 2026 · kx.studio
Web limitations
The browser edition has had missing clipboard support and reported crashes and is described as experimental in project news.Read 14 Oct 2026 · kx.studio
Web requirements
The browser build requires WebAssembly SIMD for the optimized path, while WebMIDI is limited to Chrome-based browsers.Read 14 Oct 2026 · kx.studio

Plans and prices

Cardinal Free free/open-source · fixed built-in module set · no external module installation Read 14 Oct 2026 · cardinal.kx.studio
Free 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

Every Cardinal plan and price →

Strong points and limits

Strong points

  • Free and open-source under GPLv3+.
  • Includes 1,382 modules from 84 authors or brands.
  • Runs on Linux, macOS, Windows, and the web.
  • All three main variants support MIDI input and output.

Limits

  • External modules cannot be added.
  • OSC remote control is unavailable in plugin use.
  • CLAP support remains a work in progress.
  • VST3 hosting in Carla or Ildaeil is experimental.

Who it suits

Cardinal suits musicians who want a free modular synth as a standalone app or conventional audio plugin, with a large bundled module set. It may not suit users who need to add modules or use the official Rack library.

Cardinal in depth

Read the full write-up

Cardinal is a free, open-source modular synthesizer built on VCV Rack, offered as a standalone app and as an audio plugin. It is best for musicians who want a broad, ready-made module set; the firm limit is that they cannot add to it.

Its breadth and flexible formats make it a strong no-cost starting point for modular synthesis, provided its fixed collection and variant-specific format limits fit your setup.

Overview

Cardinal packages a modular synthesis engine in a self-contained instrument, rather than relying on the official Rack library or store. Its 1,382 included modules from 84 authors or brands offer plenty to explore without assembling a collection yourself. That convenience comes with a hard boundary: Cardinal cannot load external modules, connect to the official library or store, or accept added modules in a build. It is a good fit if the bundled selection suits your work, but not if access to third-party modules is central to your workflow.

Key features

Variants and routing

The Main, Synth, and FX plugin variants all support MIDI input and output. Main provides 8 audio inputs and outputs and 10 CV inputs and outputs, giving it the most explicitly specified routing capacity. It is unavailable in AU and VST2, and the page says it is not yet available in CLAP, so users should check that their preferred host and format pair works with the variant they want.

Mini has a small hand-picked module selection, 2 audio ports, and 5 CV ports. It is available only as LV2 or standalone. That compact option may suit a lighter setup, but its narrower selection and port count make it a poor substitute for Main when broader routing matters. MPE support is also included.

Standalone controls and privacy

Standalone Cardinal supports OSC remote control of patches and parameters, a useful option for controlling a separate installation. OSC control is not available in plugin use, so it does not carry over to a DAW workflow. The project says included modules are not allowed online access such as phone-home behavior, and describes removing online access from the plugin and bundled modules.

Cardinal is licensed under GPLv3+. The project describes it as stable, while CLAP support remains a work in progress and VST3 plugin hosting inside Carla or Ildaeil is experimental. Bug reports go to GitHub; community discussion is available in the #cardinal room on Libera.Chat.

Pricing

Cardinal's Free plan costs nothing and includes a fully free, open-source build with its built-in modules. There are no paid tiers to weigh against it, but the included set is also the limit: adding modules to an existing build is not possible. This suits users happy to work within the bundled collection; those who require a customizable third-party module library should choose another tool rather than expect to expand Cardinal later.

Platforms

Cardinal runs on Linux, macOS, Windows, and the web. Plugin formats include AudioUnit, CLAP, LV2, VST2, and VST3, though format availability varies by variant: Main is not available in AU or VST2 and is not yet available in CLAP, while Mini is limited to LV2 and standalone. The standalone app is a useful route for those who do not want to rely on plugin hosting.

Who it's for

Choose Cardinal if you want modular synthesis in a conventional plugin or standalone form and value a large included collection over the freedom to install modules independently. It is especially compelling as a free, open-source option for users whose needed routing and formats match its variants. It is less suitable if your setup depends on the official Rack ecosystem, external modules, or a stable CLAP workflow.

Pros and cons

Pro: 1,382 built-in modules from 84 authors or brands provide a substantial starting collection without a purchase.

Pro: Standalone and plugin use, several plugin formats, and MIDI input and output across Main, Synth, and FX support different workflows.

Pro: OSC patch and parameter control is available in standalone use, and the project says online access is removed from the plugin and included modules.

Con: No external modules, official Rack library access, or additions to an existing build means the collection cannot grow around specific needs.

Con: Main and Mini have distinct format and I/O constraints, so not every variant will suit every host or routing plan.

Con: CLAP support is a work in progress, and VST3 hosting inside Carla or Ildaeil is experimental.

Alternatives

For a different kind of synth, DefleMask has a free legacy build described as a 32-bit unsupported demo, while its current plan costs $14.99 as a one-time purchase. Vital offers a free Basic plan with 75 presets and 25 wavetables alongside its full synth features; its $5 a month subscription adds store credit and subscriber-only packs.

VCV Rack is the closer choice if you want Rack itself: its free plan is standalone, includes free modules, and remains open-source with an open plugin API. Dexed is a free GPL v3 alternative for readers looking for another software synthesizer.

Repro is a paid alternative at €149, paid once, with two synths and a host software or DAW requirement. Helm, Surge XT, and Synth1 are other free alternatives; Synth1 is limited to macOS and Windows in the stated platform set.

Verdict

Cardinal is an excellent match for musicians who want a free, open-source modular instrument with a substantial built-in collection and both plugin and standalone options. Its main reason to choose is that breadth at no cost; its main reason to look elsewhere is the fixed module set, especially if your work depends on third-party Rack modules or an expanding library.

Verdict

Cardinal combines standalone and plugin use with a large built-in module collection and no charge. Its fixed module set and variant-specific format limits are important to consider before choosing it.

Where Specifiction places it

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