TetraOP

TetraOP is a free four-operator synth by the developer tilr, entered in the KVR Developer Challenge 2026. Its hook is that each of the four operators is both a wavetable oscillator and an FM operator, so the instrument works as a wavetable synth, an FM synth, or a hybrid of the two — the most feature-dense entry in the BPB roundup.

Architecture

• Four operators, each with 16 unison voices, five unison modes, and eight phase-distortion modes.
• Ten built-in FM/RM algorithms plus an FM/RM routing matrix for building your own — the routing-is-the-character principle applied to operator topology.
• Two multi-mode resonant filters, four envelopes, four LFOs, and four macros, over a drag-and-drop modulation setup.
• Built-in FX (compression, distortion, chorus, phaser, delay, reverb, EQ) on a dedicated FX tab; separate Mod tab.

Sonically the roundup credits it with everything from 80s bell-piano tones to synth brass to ambient media-composition beds (and an aptly named “Sharknado” preset). Available in AU, VST3, and LV2 for macOS, Windows, and Linux.

Tilr is a prolific recent freeware/effects developer (prior plugins include FILT-R and REEV-R); TetraOP is its synth entry. See kvr-dev-challenge-2026-free-synths for the source and caveats (press roundup, T3).

Related

tilr · fm-synthesis · modular-routing · synthesizer · kvr-developer-challenge · ouranos7