An improvement of convergence performance of IRWLS-based all-pass IIR filters

The paper presents a new weighting function that can be used in the method of IRWLS (iteratively reweighted least squares) for designing equiripple all-pass IIR filters. The purpose of introducing this weighting function is to improve the convergence performance in the solution of the IRWLS. The height of each weighting function is designed to be equal to the local maximum of each ripple, and the width of each weighting function is designed so that the area of each weighting function becomes equal to the area of each ripple. Here, the ripple is the absolute value of the phase error. We show experimentally that the convergence performance in the solution of the IRWLS can be improved by using the proposed weighting function.