Steady-state analysis of continuous adaptation in acoustic feedback reduction systems for hearing-aids

Acoustic feedback is a problem in hearing aids that contain a substantial a mount of gain, hearing aids that are used in conjunction with vented or ope n molds, and in-the-ear hearing aids. Acoustic feedback is both annoying an d reduces the maximum usable gain of hearing-aid devices. This paper studie s analytically the steady-state convergence behavior of LMS-based adaptive algorithms when used in continuous adaptation to reduce acoustic feedback. A bias is found in the adaptive filter's estimate of the hearing-aid acoust ic feedback path. Methods for reducing this bias and producing an improved estimate of the acoustic feedback path are analyzed and compared. It is sho wn that by the use of a delay in the forward or cancellation paths of the h earing aid plant, and for representative feedback paths, it is possible to reduce this bias by more than 15 dB.