Cardinal

Cardinal is a free modular synthesizer for musicians who want a large, ready-made module set in a standalone app or audio plugin. It is a strong fit when its built-in modules cover the job, but a poor one when a patch depends on modules from outside Cardinal.

Overview

Based on VCV Rack, Cardinal turns modular synthesis into a self-contained app and plugin. Its 1,382 built-in modules from 84 authors or brands give users considerable scope without a purchase or separate module setup. 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. That makes it a practical choice for users happy to work within a fixed collection, not for those assembling a system around a changing third-party ecosystem.

Key features

Plugin variants and routing

Main, Synth, and FX are the three plugin variants, and all support MIDI input and output. Main offers 8 audio inputs and outputs and 10 CV inputs and outputs, giving it the most specified routing capacity. Its format support has exceptions: Main is unavailable as AudioUnit and VST2, and is not yet available in CLAP. Mini takes a different approach, with a small hand-picked module set, 2 audio ports, and 5 CV ports; it is available only as LV2 and standalone. Check the variant and format against your host before building a workflow around it.

Standalone control and privacy

OSC can remotely control patches and parameters in standalone Cardinal, but not when it runs as a plugin. The project also says online access, including phone-home behavior, is not allowed for included modules and describes removing online access from the plugin and its bundled modules. That separation is relevant to users who want a local modular setup rather than one that depends on online services.

Cardinal is GPLv3+ licensed and is described as stable overall. CLAP support remains a work in progress, while VST3 plugin hosting inside Carla or Ildaeil is experimental, so those particular workflows warrant caution. Bug reports go to GitHub; community discussion is available in the #cardinal IRC room on Libera.Chat.

Pricing

Cardinal's Free plan costs nothing and includes the fully free, open-source application and its built-in modules. There are no paid tiers to unlock a larger collection, but the included build is also the limit: users cannot add modules to it. That makes the free plan a complete choice for anyone whose needs fit the bundled set, rather than an expandable entry tier.

Platforms

Cardinal is available on Linux, macOS, Windows, and the web. It also comes as a standalone app, alongside plugin versions in AudioUnit, CLAP, LV2, VST2, and VST3 formats, subject to variant-specific limits: Main is not available in AudioUnit or VST2 and is not yet available in CLAP, while Mini is limited to LV2 and standalone.

Who it's for

Cardinal suits musicians who want modular synthesis in a conventional open-source audio plugin or standalone app, and who can work within its built-in collection. MPE support and MIDI input and output across the Main, Synth, and FX variants add useful compatibility for MIDI-oriented workflows. If official support or a larger module collection is the priority, the maker points users toward Rack Pro instead.

Pros and cons

• Pro: 1,382 included modules from 84 authors or brands provide a broad starting collection at no cost.
• Pro: Standalone and multiple plugin formats give users several ways to fit Cardinal into an audio setup, with MIDI I/O in all three main variants.
• Pro: OSC remote control in standalone mode and the project's stated restrictions on online access support local control and operation.
• Con: No external modules, Rack library access, or additions to a build means users must accept the bundled selection as-is.
• Con: Main and Mini each have format restrictions, which can rule out a preferred host or plugin workflow.
• Con: CLAP is still a work in progress, and VST3 hosting within Carla or Ildaeil is experimental.

Alternatives

For a different kind of synth or music-making workflow, consider Vital, whose free Basic plan includes full synth features with 75 presets and 25 wavetables, or Surge XT, a free, open-source virtual instrument plugin for Linux, macOS, and Windows. VCV Rack is the closer alternative for users who want Rack itself: its free Rack 2 tier is standalone with free modules and open-source, while VCV says Rack will remain free and open-source with an open plugin API.

For platform breadth beyond Cardinal's desktop and web coverage, DefleMask runs on Android and iOS as well as desktop systems; its paid DefleMask plan is $14.99, paid once, while the free legacy version is 32-bit, unsupported, and described as a demo. Dexed is another free option for Linux, macOS, and Windows, licensed under GPL v3.

Sonic Pi is a free, open-source alternative available on Linux, macOS, Windows, and the web. For a pay-what-you-want standalone or plugin option, Helm is free if users choose to pay nothing and supports Linux, macOS, and Windows. Synth1 is a free VSTi/AU plugin for macOS and Windows.

Browse more options in Software Synthesizers.

Verdict

Choose Cardinal if you want a free, open-source modular synthesizer with a substantial built-in collection, MIDI-capable plugin variants, and standalone operation. Its strongest reason to choose is the breadth of that ready-to-use bundle; its decisive limitation is that it cannot grow beyond it. If external modules, Rack library access, or a particular plugin format is essential to your setup, look elsewhere.