Dehli Musikk has released Overtonium, a free and open-source additive synthesizer for macOS, Windows, and Linux.
If you like plugins with an absolute abundance of knobs, you’re in for a treat.
Overtonium presents additive synthesis like a 32-channel mixer. Every strip represents one sine oscillator locked to a harmonic of the note you play, with a separate noise channel sitting at the end.
You can set the level and stereo position of every partial, but that is only the beginning. Each one also has its own tuning, pitch and amplitude modulation, random pitch drift, velocity response, aftertouch response, and a detailed envelope with a separate key-off stage.
With so many controls, Overtonium is an incredibly deep sound-design instrument, and definitely not one for the faint-hearted when it comes to programming synths. I normally prefer simpler synth workflows, but the mixer-style interface is tons of fun, and I enjoyed exploring it during my test.
The main Tune control provides a useful starting point. It moves the partials between equal temperament and just intonation. At the just end, they sit at exact whole-number ratios and combine into one timbre. Move toward equal temperament, and the same partials snap to the closest semitones, turning the sound into more of a chord.
Overtonium goes further with Stretch and six keyboard temperaments, from Equal and Just to Pythagorean, meantone, Werckmeister III, and Young. Reference pitch ranges from 415 to 466 Hz.
Now obviously, tweaking hundreds of controls individually would get old quickly, so the Link system lets you move matching parameters across multiple channels. It can target every partial, odd or even harmonics, or partials sharing the same interval, using several weighting curves to shape the result.
The instrument also supports MPE, including per-note pitch bend and pressure. Built-in tape echo and reverb handle spatial effects, while adjustable render rate and bit depth can make the otherwise clean oscillator bank much rougher and more digital.
The 31 factory presets cover organs, electric pianos, bells, pads, and lo-fi textures. User patches are stored as editable XML files.
If you want a simpler introduction to this synthesis method, we recently covered Sound Radix Radical1 Solo. Overtonium takes the opposite approach by putting the individual partials and their modulation directly in front of you.
The download is direct from GitHub, with no account, checkout, or activation. Version 1.9.0 provides installers and ZIP files for macOS and Windows, plus a ZIP file for Linux. The Mac build is signed and notarized, but the Windows installer is unsigned and triggers a SmartScreen warning.
Overtonium runs as VST3 and standalone software on all three platforms, with AU on macOS and LV2 on Linux. The complete source code is available under the AGPLv3 license.
Download: Dehli Musikk Overtonium (FREE)
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