Not every notable MPE release this year has come with a price tag. Six Sines, the free and open-source FM synthesizer from developer BaconPaul, has just reached version 1.2, and the update adds a synthesis mode that pushes the plugin well beyond its Yamaha TX81Z-inspired origins.
From TX81Z Homage to Something Broader
Six Sines launched as a tribute to the Yamaha TX81Z, the classic '80s FM module beloved for its buzzy, distinctive four-operator waveforms. It's a 64-voice, six-operator FM synth available for macOS, Windows, and Linux in AU, VST3, and CLAP formats, and — notably for an instrument this capable — it costs nothing. BaconPaul, also known in the synth community for porting Surge to VCV Rack, has kept Six Sines free and open source from day one, with the code openly available for anyone who wants to inspect it, modify it, or build on it.
What's New in 1.2
The major addition in 1.2 is Casio CZ-style phase distortion synthesis, implemented through a new phase remap setting. Phase distortion was Casio's answer to FM synthesis in the mid-1980s CZ series, and it produces a related but distinctly different palette — sharper, more metallic transients and a different flavor of harmonic movement than true FM. Folding a phase-remap option into an already FM-capable engine means Six Sines can now cover ground that would otherwise require two separate vintage-style plugins.
Alongside the new waveshaping mode, the update continues to build on the FM engine's existing waveform set, which spans sine, square-ish, and "swish" shapes in addition to the original TX81Z waveforms — giving players a wide timbral range from clean sine tones to aggressive, buzzy FM textures, now extended into phase-distortion territory.
Built for MPE From the Start
Six Sines has supported MPE since its earliest releases, meaning per-note pitch bend, pressure, and slide all route into the synthesis engine on controllers like the Haken Continuum, LinnStrument, or ROLI Seaboard. For FM synthesis specifically, per-note expression is unusually effective: FM timbres are famously sensitive to modulation index, so mapping per-note pressure to operator levels produces dramatic, idiomatic timbral shifts that a single global mod wheel simply can't replicate across a chord.
Why a Free Plugin Matters Here
The MPE plugin ecosystem has historically skewed toward premium instruments from companies like Native Instruments, Arturia, and Expressive E — for good reason, since building a robust per-note engine takes real engineering effort. Six Sines is a reminder that serious MPE synthesis isn't gated entirely behind a purchase. For musicians who own an MPE controller but are still building out a software rig, or for anyone who wants to see how an open FM engine handles per-note modulation under the hood, it's a genuinely capable, no-cost starting point.
The 1.2 update is a free download for existing users and new users alike through BaconPaul's site, and was also covered by Synth Anatomy. Given the pace of updates so far — this is only the latest in a series of point releases since launch — it's worth keeping an eye on where BaconPaul takes the engine next.
Open Source as an On-Ramp
There's also a practical angle worth flagging for anyone new to MPE hardware. Buying a first controller is already a meaningful investment, and pairing it immediately with premium software can push the total cost of entry well past what many players want to spend before they know whether MPE playing suits them. A free, actively maintained synth with a genuinely deep FM engine removes that second barrier. It also means the code itself is available for study — useful for developers curious about how MPE data gets mapped onto per-operator parameters, since Six Sines' implementation is open for anyone to read rather than locked behind a compiled binary.