A method of determining a filter to cancel feedback signals from input signals in a hearing assistance device, comprising: measuring feedback signals for a predetermined number of feedback paths of a plurality of feedback paths associated with the device; determining a model of the predetermined number of feedback paths, the model comprising an invariant portion and a time varying portion, wherein the invariant portion comprising a finite impulse response, FIR, filter and the time varying portion comprising an adaptive FIR filter; determining a structure of the invariant portion to generate a structural constraint to constrain the predetermined number of feedback paths based on determining empirical characteristics of the predetermined number of feedback paths, wherein the empirical characteristics comprise a delay associated with the invariant portion of the predetermined number of feedback paths, sparsity of filter coefficients of an early part of the invariant portion and exponential decay of a filter tail associated with the invariant portion of the predetermined number of feedback paths; determining a prior probability distribution based on a Gaussian distribution to impose the structural constraint on the invariant portion; iteratively determining, during an Expectation Maximisation based iterative process, the invariant portion using the determined prior probability distribution and the feedback path measurements; updating, for each iteration, a measurement noise variance representative of model mismatch, to reduce a probability of a non-desirable determination of the FIR filter of the invariant portion; and determining the FIR filter of the invariant portion in response to a criterion for ending the iterative process being satisfied, wherein the determined FIR filter of the invariant portion is used by the hearing assistance device to extract feedback signals from the output of the hearing assistance device for input to the adaptive FIR filter of the time varying portion for cancelling feedback signals from the input signals. measuring feedback signals for a predetermined number of feedback paths of a plurality of feedback paths associated with the device; determining a model of the predetermined number of feedback paths, the model comprising an invariant portion and a time varying portion, wherein the invariant portion comprising a finite impulse response, FIR, filter and the time varying portion comprising an adaptive FIR filter; determining a structure of the invariant portion to generate a structural constraint to constrain the predetermined number of feedback paths based on determining empirical characteristics of the predetermined number of feedback paths, wherein the empirical characteristics comprise a delay associated with the invariant portion of the predetermined number of feedback paths, sparsity of filter coefficients of an early part of the invariant portion and exponential decay of a filter tail associated with the invariant portion of the predetermined number of feedback paths; determining a prior probability distribution based on a Gaussian distribution to impose the structural constraint on the invariant portion; iteratively determining, during an Expectation Maximisation based iterative process, the invariant portion using the determined prior probability distribution and the feedback path measurements; updating, for each iteration, a measurement noise variance representative of model mismatch, to reduce a probability of a non-desirable determination of the FIR filter of the invariant portion; and determining the FIR filter of the invariant portion in response to a criterion for ending the iterative process being satisfied, wherein the determined FIR filter of the invariant portion is used by the hearing assistance device to extract feedback signals from the output of the hearing assistance device for input to the adaptive FIR filter of the time varying portion for cancelling feedback signals from the input signals.