Complexity reduction in low-delay farrow-structure-based variable fractional delay FIR filters utilizing linear-phase subfilters

This paper proposes a method to design low-delay fractional delay (FD) filters, using the Farrow structure. The proposed method employs both linear-phase and nonlinear-phase finite-length impulse response (FIR) subfilters. This is in contrast to conventional methods that utilize only nonlinear-phase FIR subfilters. Two design cases are considered. The first case uses nonlinear-phase FIR filters in all branches of the Farrow structure. The second case uses linear-phase FIR filters in every second branch. These branches have milder restrictions on the approximation error. Therefore, even with a reduced order, for these linear-phase FIR filters, the approximation error is not affected. However, the arithmetic complexity, in terms of the number of distinct multiplications, is reduced by an average of 30%. Design examples illustrate the method.