Narrow-band and wide-band short-delay frequency-masking FIR filters
Linnéa Rosenbaum, Håkan Johansson · 2005
In this paper, we introduce a class of frequency masking (FM) FIR filters that have both short (group and phase) delay and comparatively low arithmetic complexity. The overall filter also has an approximately linear phase. Most of the delay through an FM filter originates from the model filter, especially for a large optimal periodicity factor M. The contribution is about M/(M + 1) of the total delay. Thus, when aiming for a shorter overall delay, it is most important to focus on the delay of the model filter, while the delay of the masking filter plays a minor role. The model filter is therefore chosen to have approximately linear short delay, but it is for some specifications more trouble than it is worth to also make the masking filters have a short delay. For this reason, the masking filter is instead chosen to have an exact linear phase, so that its coefficients symmetry can be exploited. With this compromise, it is possible to design FM filters with even lower arithmetic complexity and still short delay. Procedures for designing both narrow-band and wide-band FM FIR filter with an approximately linear-phase model filter and a linear-phase masking filter are given and several examples illuminate the benefits of these design procedures.