Noise cancellation for hearing aids

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. A description is given of the result of some work aimed at alleviating this problem. The approach involved the use of an adaptive array of microphones to cancel out the interference. An evaluation is presented of the applicability of the approach and an algorithm for carrying it out is proposed. 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 new autocorrelation coefficients of the true signal through the use of an instrumental variable technique. In this way, a relatively shorter filter may be used. The algorithm was successfully applied in small rooms and for free field conditions. For larger rooms, the results are somewhat degraded. A hearing test carried out with both hearing-impaired and normal people showed a definite improvement in intelligibility scores