Influence of secondary path estimation errors on the performance of ANC-motivated noise reduction algorithms for hearing aids

Current noise reduction techniques for open-fitting hearing aids that only use the external microphones on the hearing aid typically disregard the occurrence of signal leakage through the open fitting, leading to a degraded noise reduction performance. Using an ear mould with an internal (so-called error) microphone provides information about the signal leakage and hence enables to improve the noise reduction performance. Recently, feedforward and combined feedforward-feedback active-noise-control-motivated (FF ANC and FF-FB ANC, respectively) algorithms for noise reduction have been presented for such open-fitting hearing aids. The noise reduction filters of these ANC-motivated algorithms depend on an estimate of the so-called secondary path between the receiver and the error microphone. In this paper, we analyze the influence of secondary path estimation errors on the performance of the ANC-motivated algorithms. For the FF ANC algorithm it is possible to derive a closed-form expression of the filter as a function of the secondary path estimation error and to derive limit values for the allowable secondary path estimation errors. In addition, simulations show that even when estimation errors occur the FF-FB ANC algorithm still outperforms the FF ANC algorithm.