Modem receiver featuring digital phase splitting filter circuitry for storing a changing sequence of successive said samples, multiplying a single, real-valued, stream of said stored samples respectively by coefficients, and combining the products of said multiplication to provide a complex-valued output consisting of a pair of output streams having associated carrier frequencies which, due solely to the selection of said coefficients, are equal but 90.degree. apart in phase, said coefficients being selected to establish a relationship between said outputs and said stored samples corresponding to bandpass filtering having an amplitude or phase response that does not exhibit symmetry in the frequency spectrum about the frequency of said carrier, and means for thereafter demodulating and encoding said output streams.