The application of band-limited NLMS algorithm in hearing aids

Acoustic feedback is a serious problem in hearing aids. The feedback can result in whistling sound and make people who have severe hearing loss feel terrible. Traditional LMS and normalized LMS algorithm have been studied before, but these algorithms do not provide satisfactory performance for reducing feedback oscillation in hearing aids. So a band-limited NLMS algorithm is proposed. In order to determine which adaptive filter used is more suitable, we use these two kinds scheme to simulation and compare the Signal-to- Feedback-Ratio (SFR) of these two schemes, the band-limited algorithm has better performance and the output speech´s quality is better. The commonly used adaptive filter is FIR filter, but it has more coefficients and high computational complexity, so a feedback reduction subsystem based on IIR adaptive filters is proposed. Its coefficients are fewer and computational cost is lower. In this case, the IIR filter is adapted with a modified version of the NLMS algorithm for this kind of filters. It uses fewer coefficients and obtains better performance.