A post-filter for wideband speech beamforming in automotive application

Microphone arrays and beamforming for car applications have gained much attention in the past. While several proposals aim at quite idealistic conditions, our approach intentionally employs low-cost microphones. Moreover, we assume the microphone array to be integrated into the head-unit of the car. Although from an acoustical perspective this is not an ideal location, it is yet very attractive since it omits further wiring and offers a compact and optimized solution. To achieve the required level of directivity and noise reduction in car noise, the a priori noise field of diffuse noise is exploited. A new postfilter estimation using an adaptive smoothing factor along with an estimation quality indicator is proposed which is well suited for low-cost microphones. Meanwhile, an intrusive instrumental evaluation methodology will be introduced. We will show that a significant level of noise attenuation can be achieved, while the quality of the speech component will be improved compared to the state-of-the-art.