Gradient Flow Broadband Beamforming and Source Separation

We present and demonstrate a method for blind separation and bearing estimation of broadband traveling waves, impinging on a sensor array with dimensions smaller than the shortest wavelength in the sources. By sensing spatial and temporal gradients of the received signal, the problem of separating mixtures of time-delayed sources reduces to that of separating instantaneous mixtures of the gradient components of the sources using conventional tools of independent component analysis. Experimental results demonstrate real-world separation of speech in outdoors and indoors environments, using a planar array of four microphones within a 5 mm radius and analog circuits computing spatial and temporal derivatives.