Physical modeling has quietly become the natural home for expressive playing. Exciter-and-resonator synths respond to pressure and gesture the way acoustic instruments do, which is why so many MPE players end up living in Chromaphone, Rippler, Noisy or the EaganMatrix. Jas-i Khorlo, a free beta released on 2 September by developer Aaron Jasinski, takes that familiar architecture and puts it on a turntable.
The Rotating Idea
Most modal synths connect an exciter to a resonator and let you shape both. Khorlo keeps the ingredients but changes the geometry. At the centre sits a virtual glass cylinder. Arranged around it, in a circle, are up to eight independent resonators — strings, bells, membranes and other models — each of which you can position anywhere on the ring.
The exciters are the part that makes this unusual. Instead of a single strike per note, Khorlo gives you up to eight impulse rings: rotating exciters that travel around the circle and produce sound each time they pass a resonator. You set how fast each ring orbits, and — critically — which resonators it strikes and which it skips on each lap.
Ring height is the second axis. Height determines where on the resonator the ring makes contact: high positions sound bright and thin, low positions dull and round. It is a simple control with a large timbral range behind it, and the most obvious candidate for expressive modulation.
Polyrhythms as a Sound Design Tool
Because each ring has its own speed, and each can be told to hit or skip specific resonators, a single patch can generate genuine polyrhythms without a sequencer. Set three rings at unrelated tempos across differently tuned resonators and the result is a slowly phasing pattern that never quite repeats. Rings can also be tempo-synced to the host or linked to one another — what the developer describes as forming an "exciter carpool" — so the same architecture covers both free-running textures and tightly locked rhythmic parts.
Tuned conventionally, the engine also does the expected things well: plucked strings, acoustic-flavoured basses, struck metal and wooden tones. The difference is that even the conventional patches carry motion from the rotation itself.
The Rest of the Synth
Khorlo is not a one-trick experiment. Around the rotating engine sits a fairly complete modern synth:
- A dual multimode filter running in parallel or serial, with six filter topologies including clean, hybrid, comb and vowel, each with cutoff, resonance and drive.
- Eight assignable modulators with drag-and-drop routing. Each is a function generator that can behave as an ADSR envelope, an LFO or a drawable shape, with up to six destinations and its own six-slot matrix.
- Four macro controls, plus an ADSR on the VCA.
- A multi-FX section with ten re-orderable effects — chorus, compressor, delay, saturation, EQ, filter, flanger, phaser, reverb and limiter — all of which can be modulated from the mod engine.
Per-resonator editing goes deeper than the main page suggests: alongside model, pitch, detune, pan, wash and decay, a second menu exposes parameters such as stiffness and brightness, so each of the eight can have a distinct character.
The beta ships with 135 presets in a browser with tags for tone, character and articulation.
What About MPE?
This is worth stating plainly: the current beta documentation does not advertise MIDI Polyphonic Expression support, and we have not seen a per-note expression specification from the developer. So treat Khorlo as a physical modeling synth of interest to expressive players rather than a confirmed MPE instrument, and test it with your controller before building a set around it.
The architecture is, however, an obvious fit for per-note control. Ring height, ring speed, resonator brightness and stiffness are all parameters where independent control per finger would be transformative rather than decorative. It is exactly the kind of engine where MPE stops being a checkbox and starts being the point — and the sort of request worth sending to a developer while a synth is still in beta. Jasinski has been active in the comments on the Synth Anatomy announcement, so the feedback channel appears open.
Availability
Jas-i Khorlo is a free download in beta, with an official release date to be announced. It runs as VST3, AU and CLAP on macOS (native Apple Silicon and Intel), Linux and Windows. The CLAP build is worth noting for Bitwig users, since CLAP carries per-note expression natively where the plugin implements it.
Free, unfinished and genuinely novel is a good combination. If nothing else, Khorlo is a reminder that there are still unexplored ideas in modal synthesis.
More information: Jas-i