The Super Smoothers are improvements over higher-order Butterworth filters. Only after reading about regularization did I realize that the Butterworth filter consists of finite impulse response (FIR) and infinite impulse response (IIR) components, and that the FIR component could be removed, leaving a nearly maximumly flat amplitude response in the filter passband. Not only are the desirable characteristics of the Butterworth filter retained, but several bars of lag are removed due to the removal of the FIR component. The result is the Super Smoothers described.
This is a companion discussion topic for the original entry at https://www.optuma.com/kb/optuma/tools/ehlers/two-pole-super-smoother