For those interested in “FM” in its more usual Phase Modulation implementation:
Using this concept, could we do Yamaha DX style Phase Modulation (phase shifting at audiorates) with any (audiorate) oscillator as a Carrier?
Since now we can have “external” phase control, we do no longer depend on an “integrated” phase modulation input for the Carrier. The Modulator could already be any audiorate oscillator.
In this setup, both would need the same V/Oct input to generate stable pitch/spectrum.
Adding to this…
Using some form of LFO (below audiorate) and/or of “oscillator” or waveshaper (at 0 Hz) we can also emulate LFO/0 Hz Modulator “FM style” Phase Modulation Wave Shaping (or Phase Distortion).
In that case, only the Modulator needs V/Oct input. The Spectrum will be controlled by the relative initial offset of the Modulator (+ audiorate output of the Modulator + any other control signal, e.g. ADSR/LFO).
Any Carrier (oscillator) frequency above 0 Hz will produce phaseshift cycling at that rate. This changes the generated wave shape and thus the spectrum cyclicly over time. You can compare this to slight detuning of Carrier and Modulator.
But, the LFO/0 Hz “Wave Shaping” does shave a different spectral cycle, as compared to carrier and modulator at audiorates.
The Yamaha DX7 could only go down to 1 Hz (and some detuning), so, no stable spectrum. The SY77/99 go all the way down to 0 Hz. The SY77/99 also has basic initial phase angle offset settings.
BTW, NYSTHI TZOP has most of this and can also do 0 Hz (but does not seem to save this in the patch). I guess it is currently the most versatile FM/PM oscillator in VCV Rack. But…does have “limited” internal waveshapes (but more then sine only).
This Waveguide Phase control solution might further open up Pandora’s box, for “FM” (PM) options. Since we might be able to use any oscillator as a Phase Modulated Carrier.
I guess I’m gonna set up some experiments on this subject…