_02.circles Synthesizer


User Interface

An experiment in UI Design for VST plugins.

Inspired by Wassily Kandinsky's painting "Einige Kreise" this plugin was build to open an intuitive access to sound construction, modification, modulation, live performance tweaking, etc. being an interactive painting and thus a form of art by itself.

Watching that picture at the Kandinsky exhibition earlier this year I had the idea of an interactive or animated painting. At that same time I already started thinking about more intuitive user interfaces. I was a bit bored about conventional user interfaces where software resembles real instruments even showing rackmount ears. So this painting immediately caught my attention. These circles could be used for all kind of things: Knob like controllers, animations, etc.

Another idea was to open an intuitive approach to sound synthesis. Therefore the elements are not labeled (but you can always peek at the lower left corner of the status bar to see what parameter the mouse is over). Just click on an element, drag the mouse and listen what happens.

There are some guidelines though like color coding: yellow/grey is for levels, red colors are for pitch and tuning, blue is for filter settings.

Elements are grouped; more important or often used circles are bigger than others, etc. I think it's very easy to learn the elements. Then during sound programming/tweaking you know to rise the green circle a bit to get a more "grainy" sound, or adjust the pink one to make the sound "fatter".

The main page shows parameters which will mainly be used during "live performance", e.g. when recording tracks in a sequencer program. For sound programming additional windows (labeled "envelope" and "settings") can be overlaid. Note that with additional windows open the underlying elements are still working.


Interactive Demo:
  • hover mouse over elements to show parameter
  • click element to display help
  • click menu titles to slide out overlays
(image of circles synthesizer)

Sound Engine

Despite the unusual interface, there is a classic virtual analog synthesizer engine underneath the surface, simple but versatile:


  • two mib-mapped wavetable oscillators with osc spread to fatten the sound
  • available waveforms (sine): sine wave, 4bit decimated sine wave, double sine, half sine (3 types)
  • available waveforms (saw): saw wave, 4bit decimated saw wave, double saw
  • available waveforms (pulse): pulse waves with 25%, 50%, 75% duty cycle, 2 types of stepped pulse waves
  • available waveforms (additive): 6 additive waves (harmonics 1,2,3, harmonics 1,3,5 harmonics 1,2, harmonics 1,3, harmonics 1,4, harmonics 1,5)
  • additional oscillators: white noise, sub oscillator (1 octave below oscillator 1)
  • free or ratio based detuning of oscillator 1 and oscillator 2 for better spectral control when using fm, rm, ssb


  • filter types: 24 dB ladder lowpass, 18 dB lowpass, 12 dB lowpass, highpass, bandpass, notch, peak
  • overdrive build in filter for distorted sounds
  • cutoff frequency adjustable to midi note (tracking)


  • fm: frequency modulation (to be precise: it's Yamaha DX7 style fm thus rather phase modulation)
  • rm: ring modulation with upper and lower sidebands
  • ssb: single sideband modulation: like rm, but only with single sideband


  • 2 LFO's syncable to VST sequencer or free running routable to cutoff, pitch, ratio, fm, rm, ssb
  • easy adjustable graphic envelopes
  • 32 voice polyphonic or monophonic using portamento/glide

Midi Control, Automation

  • performance parameter: velocity, aftertouch, modwheel directly routable to cutoff, pitch, ratio, fm, rm, ssb
  • VST parameter automation of all "circles" on main screen (see table)
  • programs switchable through MIDI program change messages

Tips and Tricks

  • VST automation nicely animates the UI
  • the "corona" is animated when the VST sequencer runs (synced to beat)
  • LFO indicator blinks when lfo amount is on
  • use sine and additive waves with fm
  • use ratio based tuning with fm


_02.circles is available through the KVR developer contest 2009:

Download Link

Alternatively download circles from my google-sites project page:

Alternative Download Link

VST is a trademark of Steinberg Soft- und Hardware GmbH

  f last update 2009/11/27