Robustness analysis of time-domain and frequency-domain adaptive null-forming schemes

For two nearby microphones, adaptive null-forming (ANF) scheme is a simple and effective algorithm for suppressing directional noise sources. In this paper, we analyze the robustness of the time-domain ANF (TD-ANF) and the frequency-domain ANF (FD-ANF) schemes in theory. The analysis reveals several distinctive phenomena. First, the two ANF schemes reduce the amount of interference-plus-noise reduction (INR) and increase the speech distortion (SD) simultaneously as the microphone mismatch increases. Second, the FD-ANF scheme has better performance than the TD-ANF scheme when multiple spatially separated noise sources are W-disjoint orthogonal and located in the back half plane. Third, both the TD-ANF and the FD-ANF schemes are very sensitive to the microphone mismatch at low-frequency bands for most noise scenarios.