Cardinal

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 0.00 USD per free 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 USD per once. Vital offers a free Basic plan with 75 presets and 25 wavetables alongside its full synth features; its 5.00 USD per 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 149.00 EUR per 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.