High performance varible cutoff frequency linear phase filters

An approach to realizing varible-cutoff-frequency linear-phase filters is presented. Selective and computationally efficient filter structures previously developed by the author (Proc. IEEE Symp. Circuits and Systems, p.305-8, 1988) are used. It is shown how the coefficients of these filters can be fairly easily varied to obtain computationally efficient transformed filters. The calculation of the updated coefficients can be done in real-time. The resulting filters are efficient for cases where the transition band is narrow. This is because the proposed filters effectively realize pole pairs in the transition region. In this approach, the poles outside the unit circle are approximated with zeros