Extending the use of amplitude change function to stable recursive filters of any pole zero distribution

A method for extending the use of the amplitude change function (ACF), proposed by Kaiser and Hamming (1977) for sharpening the frequency response of non-recursive filters by repeated use of the same filter, to stable recursive filters of any pole zero distribution in the Z plane is suggested. A technique to extend the use of the ACF to recursive filters, with all its zeros constrained to, on or outside the unit circle, was suggested by Claasen and Mecklenbrauker (1979). We show that Claasen´s technique can be used even if the prototype filter have zeros inside the unit circle, if the numerator polynomial of H(z) has symmetric coefficients and suggest a technique to extend the use of the ACF to stable recursive filters of any pole zero distribution in the Z plane