The two halves of the system are each approximately the size of Earth's moon and orbit around each other at high speed at a distance of around 80km. Tidal forces from the two worlds have stretched them each into an egg shape and they share a common atmosphere. The capital city of Convergence is built at the point of closest approach of the two worlds and is constructed around a series of large tower megastructures that reach from one world to the other. Atmosphere capable shuttles and spacecraft can dock at the zero gravity midpoint between the two worlds and travel down to either one. Most of the planet is rural however and Convergence is the only population center larger than a few hundred. Total planetary population is approx. 6 million, virtually all of them Classic Superior (Homo superior edenensis).
The su terraformers designed the planet's ecosystem with the specific intent of creating a world in which all aspects of the eco, geo and atmospheric systems create music as a side effect. The geospheres of the planets have been sculpted to generate subtle vibration and musical notes from the winds passing over them. Plant and animal species all produce various levels and types of sounds and even the tectonics of the worlds are manipulated and shaped by technogenic devices to produce subsonic notes that contribute the overall planetary symphony. The overall effect is a subtle sense of calm well-being and heightened awareness and ability to concentrate.
The towers have to handle the elipticity of their orbits, hence telescoping nanomaterial is widely used. As a side effect these high buildings will change their resonance frequency slightly over the period, perhaps adding a time undertone to the city noise.
The colonizers were from a few neutral worlds like Eden that set out some centuries earlier. Many of the Edenese stock were descended from the old classic cislunensis (Sol System) genotype. After the Version War the world remained independent.
Harmonic-Resonance is in Sophic space, but not closely aligned to that empire, being of neutral/nominal affiliation. It is still a protectorate, although the Sophics rarely proslytise. At the same time, any pirate or raider would think twice before attacking even a nominal world in even the most contemplative and introvertive archailect empire (The Archais' willingness to employ seraphim and godtech weapons directly would probably make it even less likely that a raider would attack even a neutral world. Not to mention that a su inhabited planet could probably field some pretty high tech nastiness on its own if someone ever tried it).