First measurements of a large-aperture microphone array system for remote audio acquisition. White paper

Poor sound pick up by remote microphones in multimedia applications, conference rooms and auditoria has traditionally hampered recording and communicating among spatially-separated groups. The culprits are reverberation (multipath distortion) and interfering acoustic noise. The typical solution is to obtain close-talking pick up from participants by passing microphones among talkers, or requiring individuals to approach a microphone station. Both are unsatisfactory, time-consuming, and inconvenient. The challenge is to obtain high-quality sound pick up from microphones far from the talker that do not encumber the user by hand-held, bodywom or tethered equipment. One solution is to apply an array of microphones and sophisticated signal processing. In this paper a brief description of a large, real-time, working system is presented and early results from using this system are given. Results include measured and theoretical signal-to-noise performance, beampatterns, and the dispersion of location estimates. 2. THE ARRAY AND TESTING ENVIRONMENT An array of 256 microphones is currently being used in a square room of 8.4M on a side. The floor is hard tile and the cement ceiling is three meters above the floor. The ceiling has regular rectangular boxlike cavities that are about 4MxlMx0.3M. The array system has eight 1.34Mx0.67M panels. Each panel is an aluminum-framed piece of foam that is 6cm thick onto which 32 omnidirectional electret microphones have been placed in a random pattem. To insure a minimum separation, the pattem is random subset of the nodes of a 3cmx3cm grid. The panels are hung on walls or suspended from the ceiling in the pattem shown in Figure 1. The 256 microphones span three adjacent walls in the rectangular room. A photograph showing one comer of the array 1