Also the level of reverse engineering here is kinda bananas. I almost don’t believe he was able to find the transfer functions for the dsp bias equations w/o some source guidance. I mean that’s just bad ass if he did it without help.
I tried plotting them, and I got something that looked right when I inverted the denominator coefficients. I guess this is fairly standard practice because then the difference equation is all positive sums and it can be implemented with a bunch of multiply-accumulates.
However there were still some discrepancies in overall gain between different types (most lined up, but a couple did not). I saw another array of integers indexed by the cabinet type that had negative values, most with -23 but a couple with -12, which I figured must be a decibel gain correction. It was only after accounting for that and seeing the final graph in the post where everything lined up and looked plausible that I was pretty sure I had it right.
So, mostly just general familiarity with digital EQ filters and a bit of luck.
i'm pleasantly surprised when products don't come with all the security features :) hopefully it was their intent and not a fluke.
the amount of hoops hobbyist hackers need to jump through in order to play around is really getting out of hand.