Mildly suboptimal digital filters using a host windowing approach

Abstract

A digital-filter design technique is described which employs simple trigonometric windowing of a ‘host’ digital filter. In contrast to the usual windowing rationale which uses a truncated ideal impulse response, this approach uses an optimal (finite-length-minimax) host impulse response. It is shown that optimal Hilbert-transform filters serve as suitable hosts for lowpass filters of even-length impulse response, and optimal differentiators can be used as hosts for odd-length impulse responses. The resulting windowed filters are no longer optimal, but yield approximation errors under most operating conditions.