Detection of the Incoming Sound Direction Employing MEMS Microphones and the DSP

A 3D acoustic vector sensor based on MEMS microphones and its application to road traffic monitoring is presented in the paper. The sensor is constructed from three pairs of digital MEMS microphones, mounted on the orthogonal axes. Signals obtained from the microphones are used to compute sound intensity vectors in each direction. With this data, it is possible to compute the horizontal and vertical angle of an incoming sound. The algorithm was implemented on a low-cost, fixed point TMS320C5535 digital signal processor. The microphone signals are acquired via I2S buses, then the algorithm computes the acoustic pressure, particle velocity and sound intensity components, which are then used to calculate the azimuth and elevation of a sound source. The detection results are exposed via the USB interface. The intensity values are computed in overlapping frames in order to improve the signal-to-noise ratio. In the experimental setup, readouts with a frequency of c.a. 70 Hz, frequency range up to c.a. 9 kHz and the angular resolution of 1 degree, were obtained. Validation of the sensor was performed in an anechoic chamber using a test source with known direction. A comparison of the tested system with a commercial sound intensity probe was also made. Additionally, some preliminary tests in real world conditions were also performed. The obtained results prove that the proposed sensor and the algorithm provide high accuracy of detection of the incoming sound direction, comparable to a commercial device. Therefore, the sensor and the DSP algorithm form a low-cost system that may be used e.g. for acoustic monitoring of traffic.