If you're into Reaktor in a heavy way Native Instruments have posted some tutorials here. They take you some pretty complex stuff to do with filters.
According to Stephan Schmitt (from NI):
"The articles are in a very condensed scientific style. They definitely require some academic education and DSP knowledge. They are accompanied by two tutorials helping you to implement and to try out the discussed methods in Reaktor Core. Those who dive into this material will be rewarded by some deep insights into the design of filters."
The official documnetation for the Core system within Reaktor can be found here.