1. A signal processing system for separating signals received from plural sources via an unknown channel, comprising: a plurality of detectors each for detecting said signals received from said plural sources; and a processor for receiving the detected signals and producing a reconstruction filter for filtering the detected signals to produce reconstructed source signals in which each source signal is reconstructed without interference from the other source signals; characterized in producing the reconstruction filter such that higher-order cross-polyspectra of the reconstructed signals are forced to approach zero.