The Xhun Audio ResonHeart Mechanical Synthesizer Virtual Instrument uses ACS physical modeling based on the principals of fluid dynamics to simulate the acoustic properties of aerophone-based instruments and machines. The resulting modal synth is an unusual experimental instrument that offers unique textures with eerily real-world-sounding acoustic properties and steampunk ambience.

Rather than conventional electronic synthesis, the components inside ResonHeart have been modeled after existing mechanical hardware—commercially available devices like air pumps, pneumatic valves, and metal resonators. The instruments mimic different families of acoustic sounds and instruments including winds, membranes, cymbals, percussion, vocals, whistles, glasses, and more. The plug-in is capable of a wide variety of tones ranging from timpanic and electronic percussion and crashes to ethnic lutes, choirs, strings, and evolving pad textures.

The sound engine uses clockwork components: air pumps, motors, pneumatic valves, and complex resonator blocks (one per voice). Each resonator block consists of a set of sixteen universal Helmholtz resonators (which can be individually triggered and tuned) arranged as a modal synthesizer. The design makes ResonHeart able to accurately simulate an unusual range of acoustic sounds, including rigid-body or membrane-based percussions and cymbals—one of the hardest things to simulate using physical modeling. Surrounding room acoustics have also been carefully modeled, simulating spatial environments from small chambers to gigantic cathedrals.

The simplified interface makes the sound-designing process seamless, since all the controls and parameters are always in plain sight, arranged on its single-view panel. Trigger the main pump motor, provide energy to the air turbulence, and modify the cross-sectional area of the ducts. Tailor the internal volume and the embouchures aperture for each of the Helmholtz resonators, and add nuance by assigning different modulations for each of the pneumatic valves. Finally, place each of the resonator blocks in a space using reverb accurately modeled after real-world spaces to impart professional sheen or haunted ambience.