Steady-state analysis of continuous adaptation systems in hearing aids

Acoustic feedback is a problem in hearing aids that contain a substantial amount of gain, hearing aids that are used in conjunction with vented or open molds, and in-the-ear hearing aids. Acoustic feedback is both annoying and reduces the maximum usable gain of hearing-aid devices. This paper studies analytically the steady-state convergence behavior of LMS-based adaptive algorithms when operating in continuous adaptation to reduce acoustic feedback. A bias is found in the adaptive filter's estimate of the hearing-aid feedback path. A method for reducing this bias and producing an improved estimate of the feedback path is analyzed. It is shown that by the use of delays in the forward path of the hearing aid plant, it is possible to reduce the bias considerably.