A four-microphone noise reduction system for hearing aids
Martin Kompis, Peter Feuz, Gregory Valentini, Marco Pelizzone · The Journal of the Acoustical Society of America · 1999
A novel four-microphone noise reduction scheme for conventional hearing aids and cochlear implants is investigated. The acoustic field is sampled with a total of four microphones. Two microphones are mounted on either side of the head in behind-the-ear hearing aid housings. Each pair of microphones forms a fixed beamformer, and the outputs of the two devices are post-processed by an adaptive beamforming scheme. The adaptive beamformer is programmed to further enhance target signals emitted in the front of the listener while suppressing noise arriving from other directions. The system has been implemented in real time on a custom-built portable digital signal processing system. The output of the system can be used to drive headphones or the audio input of a number of conventional hearing aids and cochlear implant speech processors. The four-microphone noise reduction system has been evaluated in two different acoustic environments with speech recognition tests conducted on four normal-hearing listeners. Preliminary results indicate an improved directional pattern and significantly enhanced speech recognition in noise, when compared to either a fixed or an adaptive beamformer by itself. In a moderately reverberant room, signal-to-noise advantages of up to 17 dB were observed. [Work supported by the Josephine-Clark Foundation.]