Harmonic Circles III

... is a complex oscillator based on the summation, phase modulation, filtered ring modulation and frequency modulation of four sine or sine-based generators that are arranged in a feedback ring.

The generators

Harmonic Circles III is made up by

• Two wave table generators with the designations "A" & "C". These are always tuned in harmonic relation to the fundamental frequency (the one received by the Pitch In jack). All harmonics can be overtones or undertones. The wave tables are generated by the module from an admixture of the fundamental frequency and the first two odd and the first two even harmonics.
• Two sine-oscillators with the designations "B" & "D". These operate in two modes:
  • In COUPLED mode both generators will be tuned in the same way as "A" & "C". When in this mode the generators can self-modulate. The modulation type will always be phase modulation, whose intensity is controlled by the Feedback knobs to the extreme left and right of the module.
  • In DECOUPLED mode the Harmonic and Feedback knobs change their function. The first one sets a static frequency and the second one will become a Tune knob that determines the degree of interpolation between this static frequency and the frequency received by the Pitch In jack.

The modulation path

The four generators modulate each other in a clockwise fashion: "A" modulates "B", "B" modulates "C", "C" modulates "D" and "D" again modulates "A". Since many of the undertone harmonics will lie below the range of audibility, so they will act not so much as FM operators on their 'carriers', but rather as LFO-s and produce pitch or amplitude vibratos.

Further details

• A push on the orange-colored buttons will cycle through the available types of modulation for each generator: phase modulation ("PhM"), frequency modulation ("FM"), ring modulation combined with low-pass filtering ("RiM") or a simple mix with the previous oscillator ("ADD").
• The intensity of the modulation (in "PhM" and "FM" mode), the frequency of the filter (in "RiM" mode) as well as the balance of the mix (in "ADD" mode) can be controlled by the adjacent Mod Amt knobs in conjunction with the CV input jacks attached to it. Attenuators nearby regulate the influence of the input jacks.
• The output send to the Sum Out jack is obtained by summing the "A" and the "C" oscillator, the mix being set by the A + C Balance knob in the middle of the whole structure.

PS: You may notice that a little guardian inside the module prevents you from setting all four oscillators to frequency or ring modulation at the same time - such a combination wouldn't produce any sound.