It has an antisaturator in the feedback path. The working equation for finding the BP value looks like this (https://www.discodsp.net/VAFilterDesign_2.1.0.pdf fig 6.49 page 213):
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(BP - s1)/g = x - ((R-1)* (g*((BP - s1)/g)+s1) + sinh(g*((BP - s1)/g)+s1)) * 2 - g*(g*((BP - s1)/g)+s1) - s2
But sinh or tanh^(-1) lead to an unstable behaviour at high values because of the nature of the functions as described in the book. The filter blows up at higher resonance values where the filter would self oscillate.
The book describes a way to solve the equation or parts "reverse", so that sinh or tanh^(-1) can be replaced with the stable sinh^(-1) or tanh functions.
I tried a lot of things but wasn't able to solve the equation reverse. Can someone help and explain what this means and how this would be possible for the SVF?
Any other solutions to make this stable are also welcome.