Yes, interesting article, thanks for posting!
I worked on the electronics for a knock detection system for a US OEM in the last millennium and a lot of this sounds familiar.
Our main role in the magic was generating the equivalent of the knock intensity value and that was an intricate task. A lot of filtering to reject signals from the piezoelectric sensors that were not related to knocking events and windowing to identify the cylinder as well as also reject non-knock stuff. The engine gurus at our customer told us that the ideal condition was to be knocking so lightly that the sensors would barely register it and the driver would never notice it...the said this gave them the best power and fuel efficiency. They also let us watch a prototype of the system running on the dyno and it was cool to watch it adjust to changes on the fly.