An expressive, quasi-Ptolemaic semi-modular synthesizer.
Features
„Orbital Modulation“ (OM) synthesis
Randomizable modulation matrix
Built-in effects chains
Overview
Four bodies revolve with uniform circular motion, each around one of the others or, in the case of the first body, a fixed central point. Each body around which no other body revolves serves as an oscillator, producing sound. The interpretation of these terminal bodies as oscillators depends on their positions as viewed from a point that is either at the fixed center of revolution or nearby, at a point called the „equant,“ more in honor of Ptolemy than in strict adherence to his system (hence „quasi-Ptolemaic“). In the engine’s fully modulated state (i.e., with the „Demodulate“ knob turned all the way down), only the angle formed by a reference line and the line connecting the equant to the terminal body matters to the sound, just as, in Ptolemy’s system, the distances of the heavenly bodies are unknown. This system of sound generation closely resembles frequency modulation (FM) synthesis. The relative speeds of revolution of the various bodies have their analogues in the frequencies of so-called „carrier“ and „modulator“ (or „operator“) waves in traditional FM synthesis. Accordingly, the interface allows both („coarse“) whole-number and („fine“) fractional variation of these relative frequencies, producing a wide array of timbres, from the pure and simple to the densely inharmonic. Many mutually modulatable parameters are configurable by the user, and a robust system of randomization facilitates sonic exploration and discovery.
Gratitude
I’ll speak later about some of the sources of inspiration for this project, but don’t want to go any further without acknowledging that none of this would have been possible for someone like me—a humanist with an idea, not a software engineer—without the wealth of open-source tools, instruction, and advice provided freely by the community of professionals and enthusiasts. I’m especially grateful for the existence of the JUCE framework and for the many helpful extensions to it provided by Gin (which did a LOT of heavy lifting) and the visualization tools in Melatonin Blur. Early prototypes were built in VCV RACK, which was a relatively easy way to get started with audio programming and boasts a vibrant community. As a novice who needs a lot spelled out, I got quite a lot out of Will Pirkle’s teacherly books. Finally, mostly by lurking and poring over old posts, but sometimes by posing ill-formed questions and follow-ups of my own, I learned a lot on the Discord server for The Audio Programmer, mostly that other people who do this kind of thing regularly know a lot more than I am ever likely to.
Installation:
Installing Presets:
A few example presets are located here and can be installed (manually). On Windows, the install location should be %HOMEPATH%\AppData\Roaming\com.void-star\Audible Planets\programs. On Mac OS, it should be ~/Library/Application Support/com.void-star/Audible Planets/programs. On Linux, it should be ~/.config/com.void-star/Audible Planets/programs.
Pages:
The synth has four main pages: „Main,“ „FX,“ „Rand,“ and „MSEG.“ The Main page contains the main controls for sound generation. The FX page contains the built-in effects arranged in one or two chains. The Randomization page contains controls for randomizing the main parameters and modulation settings in a variety of groups, as well as a slightly different interface for the envelopes and oscillators. The MSEG page contains controls for four multi-segment envelope generators, which can act as modulation sources.
Main Page:
Mostly standard envelope, oscillator, and LFO controls take up the majority of screen real-estate here. I’ll describe some controls that are less often seen. Envelopes can be made to repeat, either freely („Free“) or in subdivisions or multiples of the beat („Sync“). With the „Tones“ knob set to minimum and the „Saw“ switch set to „Off,“ the motion of the body is uniform and circular. In this mode, adjusting the relative starting points of the various oscillations (with the „Phase“ control) can change the sound a lot. When „Tones“ is turned up, the motion of the body is no longer uniform and circular, but is modulated with extra whole-number multiples of the main frequency up to 5. The „Saw“ switch turns the motion into a diagonal sawtooth wave. Both enrich the spectrum of the oscillator, but have different effects on the final sound depending on the level of the „Demodulate“ control, which effectively determines the amount of phase modulation. The „Sidechain“ switch changes the motion of the first oscillator to a semicircular projection of whatever audio is piped in. In addition to these ways to enrich the individual „spectrum“ of each oscillator, there is a general „Blend“ control in the „Timbre“ section, which takes the interpretation of the bodies‘ positions as phases, not of a pure sine wave, but of a mix of sine, saw, and square waves. The presence of „Detune,“ „Spread,“ and „Pan“ controls for each oscillator indicates that the orbital algorithm described in the overview above is computed for multiple voices over two channels, and slight variations in position and frequency between the latter can bring movement, width, and depth to the sounds produced. Finally, the LFOs have delay and fade-in controls, which affect the per-voice (or „poly“) modulation source. (More on that distinction when we discuss modulation.)
In the Timbre section, in addition the „Blend“ control, there’s one that modifies the position of the equant, the point from which the motions of bodies are observed. The function of the „Demodulate“ knob has already been described, but I will add that in many cases, turning it up tends to mellow the sound, removing the sideband frequencies produced by the orbital algorithm, making it function more like a rudimentary additive synth. Furthermore, since the size of all the orbits is variable, the audible planet or planets may pass very close to the equant, or even through it, resulting in sharp corners and/or discontinuities. This could (and can) be avoided by making the outer orbits smaller, but that also reduces their contribution to the overall sound. The „Squash“ control flattens the outer orbits along a tangent to the central orbit, as seen below.
This brings them farther from the center without diminishing their effect as much as reducing their radii would, since the modulated portion of the signal depends only on the angle about the center (or equant, if displaced). That said, if you begin with a configuration where epicycles are sufficiently small, increasing the „Squash“ factor will introduce new harmonics, sharpening the sound. Finally, the „Algorithm“ control switches between different arrangements of the oscillators, with the „terminal“ body or bodies being indicated by parentheses. In many cases, the first algorithm 1-2-3-(4) is the harshest, and the last the least harsh, but the effects vary depending on the relative sizes of the orbits, so it’s worth trying out different algorithm settings as you’re trying to dial in a sound.
The global parameters include controls for monosynth and legato modes, glissando and portamento at an adjustable rate, velocity sensitivity, pitchwheel range, and overall volume. There’s also a dedicated per-voice filter, with cutoff, resonance, and key tracking controls, and a variety of common filter types.
The partially open circles found in various panel headers, as the section in the top right indicates, are sources of modulation. The single-line versions are „mono“ and the double-line versions „poly,“ which is to say the latter are different for each key press (or subsequent pressure, tilt, or slide, on MPE-capable MIDI controllers). To use any of them, click and drag from the source to the destination. Almost any knob can have its setting modulated, and that goes for the effects controls on the FX page and the MSEG controls as well. When a parameter is modulated, a small orange circle appears in the upper-right corner of the control. Clicking and dragging it (or using a mouse scroll wheel while hovering) will increase or decrease the modulation amount, in a positive or negative direction, or both. (More spacious sets of modulation controls reside on the „Rand“ and „MSEG“ pages.) Right-clicking the small circle will give the option to remove any or all of the modulation sources attached to it. Small white dots on the periphery of the control indicate the modulated value or values of the parameter for whichever voices are active.
The orbit visualization can be slowed down or sped up with the Orbit „Speed“ control and you can zoom in or out with the „Scale“ control or by hovering over the orbits and scrolling the mouse wheel.
Effects Page:
The effects (FX) page contains slots for up to eight built-in effects, arranged in one (when „FX Chain Routing“ is set to „A -> B“) or two chains („A || B“), each with its own gain control, applied before the signal enters the chain. Ordering the effects chains differently can open up a lot of possibilities. Since the effects parameters can be modulation destinations, there’s a mod sources panel on this page, too. Also, since there’s room for it, there’s a modulation matrix panel, showing the currently active modulations, and offering controls to bypass, adjust, or delete them. In combination, the effects on this page can add a lot of boost, especially when modulated with sources that can constructively interfere. A built-in limiter is accordingly always on and meant to keep the levels below 0 dB, but be careful nonetheless.
Randomization Page:
Sound design can at times be a game of „almost, but not quite.“ At other times, good results can come from unexpected synergies and, frankly, from a more kitchen-sink approach. The randomization page is meant to facilitate both: gentle nudges and total crapshoots. The large modulation matrix panel offers the most fine-grained interface for adjustment, while the buttons in the columns to its right change several or even many settings at once. Generally, things in the left column add modulation or randomization and things in the right remove it. The sliders for „Number of Mods“ and „Randomization Chance/Amount“ control the „how many“ and „how much“ of these randomization buttons. The „Inharmonic“ checkbox allows modulations and randomizations to be applied to the oscillator „Fine“ controls and the global „Pitch“ control, which quickly produce inharmonic or atonal results. The „Reset Inharmonic“ button below it removes any such mods without deleting any others. Other buttons with arrows in their names refer to groups of parameters: „LFO“ and „ENV“ are self-explanatory, „Keys“ includes velocity, MIDI note number, the pitchbend and mod wheels, and „MPE“ pressure and timbre. (The latter, as well as per-note pitchbend, can be activated using the „MPE“ option in the top-left menu). The parameters of whatever effects are currently active can be modulated with „Randomize FX Mods“ and the order and selection of effects can be randomized with „Randomize FX Choice.“ The bottom row of buttons doesn’t add any new modulations, but increases or decreases those that are already active. Since it’s annoying to have to switch pages while one is adjusting parameters, a second set of mostly complete envelope and oscillator controls are on this page. That said, if you click once anywhere within the plugin screen, you can change tabs with the „1,“ „2,“ „3,“ and „4“ keys on your keyboard.
MSEG Page:
The MSEG page exposes controls for producing arbitrary control signals, single or repeating, with many of the same parameters as the LFOs on the main page. Double-click to create points, which you can click and drag to their desired locations, or turn on „Draw“ and select a draw mode from the drop-down menu. All control points will snap to grid lines they are near. Scroll with the mouse wheel to adjust the number of horizontal divisions in the grid, and scroll with a modifier key held down (e.g., control, shift, alt) to adjust the vertical grid.
