Performance of real-time source-location estimators for a large-aperture microphone array

A large array of microphones is being studied as a possible means of acquiring data in offices, conference rooms, and auditoria without requiring close-talking microphones. An array that surrounds all possible sources has a large aperture and such arrays have attractive properties for accurate spatial resolution and significant signal-to-noise enhancement. For the first time, this paper presents all the details of a real-time, source-location algorithm (LEMSalg) based on time-of-arrival delays derived from a phase transform applied to the generalized cross-power spectrum. It is being used successfully in a representative environment where microphone SNRs are below 0 dB. We have found that many small features are required to make a useful location estimating algorithm work and work well in real-time. We present an experimental evaluation of the current algorithm's performance using data taken with the Huge Microphone Array (HMA) system, which has 448 microphones in a noisy, reverberant environment. Using off-line computation, we also compared the LEMSalg to two alternative methods. The first of these adds local beamforming to the preprocessing of the base algorithm, increasing performance significantly at modest additional computational cost. The second algorithm maximizes the total steered-response power in the same phase transform. While able to derive good position estimates from shorter data runs, this method is two orders of magnitude more computationally expensive and is not yet suitable for real-time use.