Mutant Brain configurator for your browser

Brainstem is a free, open-source web app for configuring the Hexinverter Mutant Brain, a 16-output MIDI-to-CV Eurorack module. Edit every CV and gate output visually, send patches straight to the module over Web MIDI, and import or export .syx files — no install, no account, nothing to sign up for. Everything runs locally in your browser.

What you can do with Brainstem

• Edit CV and gate outputs visually. The editor mirrors the module's front panel: four CV outputs (A–D) and twelve gate/trigger outputs (01–12), each one clickable.
• Map notes, CCs, clocks and triggers. Set the source, MIDI channel, note range, CC number and clock division for each output.
• Start from a ready-made profile. Built-in patches cover polyphonic voices, drum and trigger layouts and other common setups.
• Send over Web MIDI. Push a patch to the hardware directly from the browser — no separate MIDI utility required.
• Import and export. Read and write .syx files and a JSON profile format, and save profiles to your browser.

A modern alternative to Mutant Brain Surgery

Hexinverter's official Mutant Brain Surgery patch builder was built for an older web. Brainstem is an independent, browser-native alternative: it opens in a normal tab, needs no plug-in, and can talk to the module directly over Web MIDI. If you are looking for a Mutant Brain configurator that works on a current computer, this is it.

Frequently asked questions

Does Brainstem work in my browser?

Patching works in any modern browser. Sending a patch to the module over Web MIDI needs a Chromium-based browser (Chrome, Edge or Brave) on a secure connection. Importing and exporting .syx and JSON patches works everywhere.

Is Brainstem free?

Yes. Brainstem is free and open source under the MIT license, with no account, no ads and no tracking.

Is Brainstem the same as Mutant Brain Surgery?

No — it is an independent alternative. Brainstem runs in any modern browser with no plug-in, flash or Java required, mirrors the module's front panel, and can send patches straight to the hardware over Web MIDI.

How do I get a patch onto my Mutant Brain?

Connect the Mutant Brain over USB, click Send to Mutant Brain and allow MIDI access when the browser asks. You can also export a .syx file and load it with any standard SysEx librarian.

Does Brainstem work with the CV.OCD?

The Mutant Brain and CV.OCD share the same NRPN-style SysEx configuration protocol. Brainstem targets the Mutant Brain; the same patch concepts carry over to the CV.OCD.

Credits

Brainstem is an independent, unofficial tool. It is not affiliated with or endorsed by Hexinverter Électronique. The Mutant Brain, its SysEx protocol and the referenced documentation are the work of Hexinverter and the open-source community. Source code is available on GitHub under the MIT license.