Hi,
I'd like to implement in pure data the tone stack model I found in the DAFX book. It's a linear third order transfer function. In the book they use mathlab which seems to have a routine to solve it so the code they give is of no use to me.
In pd, should I find the roots of both third order polynomials and use poles and zeros objects like in Maelstorm tutorial? Does his method transpose? Should I use fexpr~ instead? Is there another method?

Tone stack in pd

so far my best guess would be https://en.wikipedia.org/wiki/Cubic_equation#Trigonometric_solution_for_three_real_roots

Wew lads! What a complicated topic. Finding real roots for the denominator, finding either 3 real or 1 real and 2 conjugated complex roots for the numerator... The current filter is 100% highly unstable, I hope I'll get it working eventually.

so I totally gave up on solving my maths problems in pd. I used FAUST instead and run my tonestack~.dsp in [faustgen~].
you can access the 3 parameters with [low/med/top $1( from 0 to 1.
first time with FAUST, looks awesome.