Assessing the benefit of adaptive null-steering using real-world signals

This study compared the noise reduction of adaptive null-steering and near-hypercardioid directional hearing-aid algorithms via performance on real-world signals. Using subject-individualized and generic (i.e. similar to current hearing aids), off-line frequency-domain implementations, we processed recordings made through two microphones of a BTE device worn by five subjects. Recording scenarios included homes, offices, cafés, streets, buses, and automobiles. We found practically all (> 95% of recording time) adaptive noise-reduction benefit for generic implementations is below 1.2 dB, and 96% and 92% is below 2 dB for 16-and 32-band individualized implementations, respectively. A 256-band, individualized implementation showed a majority of benefit between 1-4 dB. We found no extended (> 2 s) continuous periods of significant (> 2 dB) benefit for the generic adaptive implementations. The recordings-having many independent and simultaneously active sources, spatially extended sources, significant reverberation, or combinations thereof-indicate an environment comprising few instances of high direct-to-diffuse energy situations. Combined with results from previous field trials, the evidence suggests that such an environment is common and represents a significant limitation on adaptive benefit.