I followed the code path when you change the cabinet type, and saw it write some values to the DSP based on a 2D array of doubles, one for each cabinet, each with 41 values, and it was processing them 5 at a time. Looking at the values, they were all in the range -2 to 2, and were very reminiscent of biquad filters I had learned about in another project (https://mforney.org/blog/2025-06-06-babyface-midi-protocol.h...) which was still pretty fresh in my mind.

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.

Sorry WHAT?! I was under the impression this whole time that this wasn't feasible due to asymmetric key encryption with the private keys baked deep into the hardware. Perhaps I'm misremembering but Cliff (the founder) is very big on protecting trade secrets so I'm rather surprised you were able to. Or do you mean you were able to flash new firmware, not reverse-engineer the existing one?

Either way I don't blame you for not writing it up. The same guy just recently accused another industry player of "infringing on [his] idea" with a product because he "filed a preliminary patent". I've been using Fractals since long before they were cool but based on the guy's forum posts I think he's having a hard time navigating the modern internet cultural landscape (the tenuous nature of his legal argument notwithstanding). It's a real shame as he's clearly super talented but I think trolls have gotten to him.

Unfortunately there were no firmware updates for the THR10c, so the only way to get the firmware is to dump it from the device.

Would love to see this done for the Spark amp as well, this level of hardware hacking is beyond my skill set.

I recently built my own Multi FX app/plugin (https://guitar.soundshed.com) and am looking for ways to squeeze it (or a version of it's signal chain) into commodity hardware as replacement DSP signal chain.