Wideband maximally flat fractional-delay allpass filters

The maximally flat (MF) fractional-delay (FD) allpass filter, also known as Thiran´s allpass filter, is one of the most popular IIR FD systems which is typically deployed in its causal forms. It is shown that if this causality constraint is removed, MFFD allpass filters with considerably wider bandwidths can be obtained. In many applications this extra bandwidth is worth having a non-causal system.