systems and techniques for measuring the performance of a communications channel is disclosed which includes receiving a signal from the communications channel , filtering the signal , estimating a bias introduced by the filtering of the signal , and computing a parameter of the communications channel as a function of the estimated bias . it is emphasized that this abstract is provided to comply with the rules requiring an abstract which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure . it is submitted with the understanding that it will not be used to interpret or limit the scope or the meaning of the claims .