Adaptive Noise Cancellation for Hearing-Aid Application

Noise reduction systems using two or more microphones are generally more effectj-ve than single-microphone systems. Under ideal conditions, an adaptive two-microphone system with one microphone placed at, the noise source can achieve perfect cancellation. For hearing-aid applications it is not usually practical to place a microphone at or near the noise source. It is possible, however, to mount both microphones on the head with a directional microphone facing the noise source and an omnidirectional microphone picking up speech plus noise. In practice, there is continual movement of the head relative to the speech and noise sourc:es which may adversely affect the adaptive cancellation algorithm. Another practical problem is that of room reverberation. A head-mounted two microphone adaptive noise cancellation system was evaluated experimentally in an anechoic chamber and in rooms, with reverberation times of up to 0.6 seconds. Significant improvements in speech intelligibility were obtained with both normal-hearing and hearing-impaired listeners.