The inspiration for the SF-2 was we figured we could cut the cost by 75% of putting the Superfilters onboard by putting them in a rack unit - there's just a lot more room than inside the body of a bass or guitar.
My dad's interest in filters came from when he worked at Ampex in the late sixties. We purchased Universal Active Filters from KTI. Academics later termed these state variable filters but they are the same animal as I understand. We still have all the handbooks and datasheets from the late sixties in my dad's library.
The first Superfilter not installed in a bass was made in about 1970. There is a picture of my dad with one of the first ones he made on
Ikebe's website. After the KTI filters weren't available anymore, we began making our own. We installed KTI and ones we made in instruments and as outboard units like the one in the picture.
I don't think my dad has Craig Anderton's book, so I suspect your independent evolution theory is correct. Dad has always told me the stuff to invent things is around for years and years, just waiting for someone to put it together.
