Development of a speech-distortionless beamformer for two-microphone digital hearing aids

To enhance noise reduction performance for digital hearing aids (DHA), this study proposes a speech-distortionless beamformer which is realized by a sequential processing of fractional delay, subtraction and integration (FDSI). A Simulink model of this beamformer was constructed and its performance of speech quality enhancement was evaluated in various noisy circumstances including babble, car and traffic noises. In this simulation, null direction of the beamformer was fixed at 120° azimuth and noise source position was altered from 100 to 140° azimuth. The distance between two microphones also varies from 8 to 20 mm. Compared to conventional beamformers, the FDSI beamformer showed higher frequency-weighted segmental SNR (fwsegSNR) and lower weighted spectral slope (WSS) while perceptual evaluation of speech quality (PESQ) was almost same in every beamformer. These results imply that speech distortion was significantly reduced. Therefore, the FDSI beamformer has great promising for speech quality enhancement in DHA.