an adaptive filter 24 adaptively filters a signal and updates a plurality of coefficients stored on capacitors 69 to minimize the error between the filter output at 72 and a set of notional reference values supplied by a reference generator 74 . the stored values of one or more coefficients are monitored and if the monitored coefficient or coefficients pass respective thresholds or leave respective ranges , indicating the onset of maladaption a default set of coefficients is forced .