Noise Cancellation for Hearing Aids

Abstract

The usefulness of hearing aids is severely limited by the existence of the “cocktail party effect.’’ This is due to the very high sensitivity of hearing aid wearers to interfering sounds. The purpose of this work is to describe the results of some work carried out at the IBM Israel Scientific Center aimed at alleviating this problem. The approach adopted involved the use of an adaptive array of microphones to cancel out the interference. This paper evaluates the applicability of the approach and proposes an algorithm for carrying it out. A unique feature of the algorithm is the use of a measure of fit of the resulting signal to the true signal which matches only the first few autocorrelation coefficients of the true signal through the use of an instrumental variable technique. In this way, relatively shorter filters may be used. The technique requires only that the user identify to the system silent periods of the main speaker during start up or when tracking is lost. The algorithm was successfully applied in small rooms and for free field conditions. For larger rooms, the results are somewhat degraded. A hearing test was carried out with both hard of hearing and normal people, and a definite improvement in intelligibility. © 1988 IEEE