Approximately linear phase IIR polyphase filter design

An approximately linear phase allpass polyphase structure is presented which consists of a nonlinear phase allpass polyphase network cascaded with a allpass equalizer. The equalization is done at the input of the polyphase network in the interpolation case and at the output in the decimation case so that it can be performed at the lowest sampling rate. The authors also present correction filters to suppress the inherent `don´t care´ bands of allpass polyphase structures. The suppression is also done at the lowest sampling rate