Interpolating and Nyquist filters with constraints at certain frequencies

Abstract This paper presents modifications to procedures for designing FIR interpolating filters and FIR Nyquist filters that allow the output of the filter to be error-free for certain input frequencies. For a minimum mean-square error interpolator, the modifications result in an expanded set of linear equations which include the constraints. For minimax stop-band Nyquist filters, the modifications involve factoring out a filter which implements the constraints on the transfer function. Approximate techniques for implementing the constraints are also discussed.