karn@eagle.UUCP (Phil Karn) (09/01/83)
Oops, I made a mistake when I said that ALL low or high pass filters have an ultimate attenuation that is a function only of the filter's order. This is only true for all-pole filters, as rabbit!jj pointed out. Elliptical (Cauer) filters, which have zeroes in the stop band, will have an ultimate attenuation of 6 or 0 db/octave depending on whether the filter is of even or odd order. However, both Butterworth and Bessel high or low pass filters are all-pole and have ultimate attenuations of 6 db/octave/order. Phil