VARIABLE DIGITAL FILTERS.

Abstract

Different possibilities for the implementation of a variable digital filter are reviewed, especially for the case of a selective filter with cutoff frequencies subject to change. It is shown that a combination of a coefficient calculator and a digital filter is suitable to overcome the difficulties which arise when the allpass transformation is directly applied to the implementation. An even higher flexibility is achieved if a microcomputer is used to design the filter for given specifications, and if its speed is sufficiently high to carry out the filtering operation in real time afterwards. Different possibilities have been investigated and checked experimentally.