About the RCA Theremin sound a lot of philosophy exists. Good analysis was made by Mike Buffington, RCATheremin.com, mentioned already twice in this thread. Also german Alexander Klaus, Aetherwellen-musik.de, got to the bottom of this sound and timbre.
I attempt to re-create that old sound with a new concept, based on transistors. Here my video about.
RCA Theremin sound re-creating
Hope it's of interest in this theremin community here.
Interesting topic, thanks. If I had seen it before, I would not have created my own topic about the complexity of timbre formation in simple theremins.
At the beginning of the topic, the area of the sound of the clarinet and the quacking of a duck was touched upon, and a reference to the type of oscillators that give a specific, "clarinet" waveform, when the sinusoid peaks have a narrow shape, may be useful. In the article, this is associated with relaxation generators, which, at one time, are made on such elements that give such a form. For example, unijunction transistors.
https://www.waitingforfriday.com/?p=334#Relaxation_Oscillator
JP your sound is the very nice Theremin Phenomenon, you must have an analog radio background?
Christopher
Edit: Been drinking my whiskey, JP people will want a simple answer to our sound but we both know it borders the mystical and you and I were invited. Now going forward I recognize you as a very special person.
Back to basics.
The envelope of the usual addition of fixed and variable RF signal follows - after rectification and RC filtering - a simple square root of the law of cosines function. If both amplitudes are equal, a time signal and a fft spectrum is obtained as shown here in the Ltspice simulation. If these amplitudes are different, the envelope is more and more sinusoidal. Harmonics then disappear almost completely.
Etherwave and most analog theremins use the first case with equal amplitudes. The audio signal is then further shaped, for example with a limiter or a non-linear amplifier stage.
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