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FM of Filter cutoff via operator output

It would be cool if the filter frequency could be added as a destination of at least one of the operators.
What works already is routing a looping envelope to the filter cutoff frequency and tune it e.g. by note number, but this is not very controllable, because the envelope scale and time modulation resolution is too steppy to get a per key matching pitch of the cutoff frequency modulation. Its useful as an FX, but not very playable.
LFO to filter frequency works, but it is low frequency only, unfortunately, and it consumes the only LFO available (apart from the operators used als LFOs, but they cant be routing matrix sources themselves).

If an operator output (e.g. of operator 1) could be routed to the filter cutoff, this would open up many possibilities in sound desing using the already existing Filter.
Maybe you could put this into the menu of operator 3, where there is no feedback parameter in the menu?
Or you could show the filter in the overview similarly to the operator blocks so that the filter can be routed as a destination similarly like routing is done for Operators, or even put the filter between operators, instead of at the end of the chain? I guess that would not eat a lot more additional processing power.

Alternative would be to directly enable Operator outputs as sources in the routing matrix, to be able to route them to filter cutoff frequency (and all the other destinations).
This is not possible, because in the EssenceFM modulations run at about 700Hz (700 times per second).
It can go somewhat in the audio range but not with high enough precision to be useful to have operator outputs as sources.
I often wonder about this. If you use an exponential moving average in the filter code, which must traverse that memory anyway, you could have a low pass to 700Hz. Very cheap in terms of CPU/memory access budget. Would it be musically useful? A single parameter could be used to further reduce the effective cutoff frequency. That would be rich. Let’s say the 700Hz modulation signal just exists as a modulation source, like another kind of LFO. I haven’t tried this to evaluate how useful it would be, but it would be easy to try out by hacking on dexed or say on the sub37 by running the audio out through an external low pass filter with the same transfer function as the exponential moving average. Then back in as a CV mod source.

If it sounded good and the GUI problem could be solved then it would be unique and cool as a synth feature. A variable multiple band pass filter and compressor in the control frequency range is another more expensive way to synthesize a control signal from audio. If the frequency response peaks could track the note number that one could do magic. There could be a calculated response so that sub harmonics of the note fundamental within the desired range would be selected. But that last would be very expensive… Should be musical though.
We can add operators' outputs as a source in the mod matrix, that would make them useable as LFOs that controls many things (it's already possible to use operators as vibrato LFO, by using them as modulators).

It will work well with frequencies up to a few hundred Hz, then it won't above 700Hz but that could be used intentionnally for some effects, like people use high modulation indexes to create aliasing
That is really cool that you would even consider this. It would be neat to see if this works and is musical. This remains my favorite synth because you made it so easy to build very complex layered patches. I feel like it is a kind of user interface genius that is unique.