This time, it’s time for the impossible!
As in, there was a reason nobody was doing sweepable, ‘synthy’ biquad filters…
Turns out it simply doesn’t work. One uses a different type, like state variable filters, for the synthy stuff. The reason is that, while biquads can sound pretty great (especially implemented like I do ’em), they fundamentally can’t cope with changing the filter coefficients mid-calculation. They flip out: you’ll hear some of that, especially at the frequency extremes. Low Q makes low frequency motions flip out, and high Q (and boy do I have a high Q for you this time) makes ultra-high frequency motions flip out in a really wild. glitchy way.
So obviously I gave up.