A Free-Source Method (FrSM) for Accurately and Quickly Calibrating a Large-Aperture Microphone Array

Large-aperture microphone arrays can be used to capture and enhance speech from individual talkers in noisy, multi-talker, and reverberant environments. An important factor for their use is array calibration. Due to the size and complexity of these arrays, direct-measuring techniques such as using a measuring tape or a laser-based tool are too cumbersome and time consuming. Previous methods that used acoustic signals for array calibration worked well for smaller arrays, but they had the disadvantage of establishing a coordinate system based on the sound sources whose positions had to be measured precisely. This not only limited the number of source locations that could be used for calibration but also made inevitable re-calibrations tedious. This paper describes a new and robust method for automatic calibration using acoustic signals that not only establishes a fixed coordinate system on the microphones but also significantly simplifies the process in general. This method requires only a single speaker with a microphone attached above its center. The unit is freely moved around the focal volume of the microphone array for a single long recording from all the microphones. We describe the method, validate its effectiveness and compare the results against measured ground truth and some previous methods for a real 128-microphone array.