Sound Radix has released Radical1 Solo, a free monophonic version of its additive synthesizer Radical1, giving producers a zero-cost entry point into the company's spectral synthesis engine — and one that's built with MPE performance in mind.
From Polyphonic Powerhouse to Focused Free Tool
The original Radical1 launched as a modular additive synthesizer capable of near-infinite sound design, built around layered oscillators and deep spectral manipulation. Radical1 Solo takes the same core engine — the same oscillators, modulation system, filters, and effects as the paid version — and strips it down to a single voice and a single layer, aimed squarely at basses, leads, and sequenced lines rather than complex polyphonic pads.
That focus makes it a lighter, more approachable starting point for producers who found the full Radical1's modular routing intimidating, while still giving them access to the same sound-shaping tools under the hood.
Sound Design Tools Worth Noting
Radical1 Solo carries over several of the flagship engine's more distinctive features:
Morphing Fluid Oscillators allow continuous reshaping of harmonic content in real time rather than switching between fixed waveforms. Direct Spectrum Drawing lets sound designers manually sculpt a sound's harmonic makeup by drawing directly into its spectrum. Spectral Sample Resynthesis goes a step further, converting an audio recording into a fully controllable additive structure — effectively letting a sampled instrument or field recording become a playable, modifiable synth voice.
Because Radical1 Solo is MPE-ready, all of these parameters can be mapped to per-note expression data. A single sustained note played on an MPE controller can have its harmonic content reshaped in real time by timbre (Y-axis) movement, while pressure and glide reshape amplitude and pitch independently per note — the kind of continuous spectral control that additive synthesis is particularly well suited to, since harmonics can be added or removed smoothly rather than through the harder transitions typical of subtractive filtering.
A Practical Upgrade Path
Sound Radix designed Solo as a genuine on-ramp rather than a stripped-down demo: patches and sound design work created in Radical1 Solo remain fully compatible if a user later upgrades to the full polyphonic Radical1 instrument. That removes the usual risk of investing time in a free tool only to have to start over when moving to the paid version.
The plugin is available now in VST3, AU, and AAX formats for macOS and Windows, as a free download from the Sound Radix website.
Why It's Worth Trying
Additive synthesis has a reputation for being complex and CPU-hungry, which has historically kept it out of reach for casual sound designers — and largely absent from free plugin catalogs. A free, MPE-ready additive synth lowers that barrier considerably, giving MPE controller owners another engine to experiment with beyond the usual wavetable and subtractive options that dominate the free-plugin space.
For musicians building out an MPE-focused plugin folder, Radical1 Solo is a low-risk way to explore spectral sound design and hear how additive synthesis responds to continuous per-note control — without committing to the cost or complexity of the full Radical1 engine.