I've found that the selection of the freeks is important, to say the least. Most important is to make sure that the tonal and volume oscillators are not whole multiples of each other.
These frequencies are very critical as I recently discovered, at least with my Kepp design. Shifting the tone oscillator frequencies more than a certain amount affects the tone. In my case. the two tone oscillators hovered around 205 KHz, while the volume was around 415 to 420 KHz. This arrangement caused issues. So, I dropped the two tonal oscillators down to around 194 KHz. This change eliminated the nasty birdies and fixed the volume loop response. The tone, however, was cleaner but had an entirely different, but not unpleasant sound. I think 194 KHz was too low as the pitch rod response suffered in the higher registers.
I can see how all the art and science of the theremin art has drove many a sane person mad. I've not devoted a whole lot of effort to this issue as I have more science than art in my character.
PHILIP
