On employing cascaded adaptive filters for acoustic feedback neutralization in digital hearing aids

In this paper, we propose a novel solution for continuous acoustic feedback neutralization in digital hearing aids. The proposed method is based on two adaptive filters working in tandem. The error signal of the first adaptive filter is used as a desired response for the second adaptive filter, which is excited by a low-level (constant) probe signal. Initially at the start up, the first adaptive filter gives fast convergence, however, it may converge to a biased solution in steady state because its input and desired response are correlated with each other. On the other hand, the second adaptive filter, though converging slowly being excited by a low-level probe signal, would give good estimate of the acoustic feedback path in steady state. In order to avoid the misconvergence of the first adaptive filter and speed up the initial convergence of the second one, their weights are exchanged, making sure that both adaptive filters give good estimate of acoustic feedback path. Computer simulations suggest the improved performance of the proposed method.