Design of 1-D variable fractional delay all-pass filters using stability controlling

In this paper, a two-stage approach for the design of general 1-D stable variable fractional delay all-pass filters is proposed. The method takes the desired group delay range [N-1, N], where N is the filter order. The design algorithm is decomposed into two design stages: Firstly, a set of fixed delay all-pass filters are designed by minimizing a set of objective functions defined in terms of the approximating error criterion and the filter stability constraint. Then, the design result is determined by fitting each of the fixed delay all-pass filter coefficients as 1-D polynomials. A design example together with its comparisons with those of the recent literatures is given to justify the effectiveness of the proposed design method.