Analytical Services
Acoustic modeling and analysis
A company was interested in how a “listening” system can determine the directions of multiple sound sources from multiple microphones. We implemented an algorithm to detect coincidences of energy at many frequencies, between any pair of microphones.At any frequency, the peaks of a pure-tone sound wave at one microphone are coincident with peaks at the same time (or phase) in the other if the microphones are separated by any whole number K of wavelengths along the wave’s path. For any K, there is a corresponding direction of the sound wave. With many possibilities open for the correct K, there are many possibilities for the direction. This is what makes pure-tone sources so hard to localize with our ears.
Most sound sources, however, produce time-varying energy at many frequencies. By watching for the few directions that are possibilities for many frequencies at once, and by building up the information over time, the system can begin to determine the directions of sources, even of multiple sources present at the same time.
In practice, typical sources come in such a variety that the algorithm produces many false alarms until it has a very large amount of data. We therefore implemented a matched filter for the coincidence pattern that it produces, in order to suppress most of the false alarms while retaining the true detections.
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