Calibration of mobile device microphones and their use for sound source identification

Abstract

With the advancement of mobile device technologies, many studies are focused on the improvement of the sensors within these devices thus searching a way to use mobile devices for professional applications. The critical improvements in these sensors allowed these devices to be used as professional measurement tools as well as a communication tool. The main purpose of this thesis is to investigate the performance of built in microphones within the mobile devices and to calibrate the mobile microphone with comparison to a reference condenser microphone. The performance of mobile device microphones are investigated in different mediums to define the effects of these mediums on the measured sound pressure values. Moreover, the sound source identification of a vehicle is also conducted in this thesis with a developed android application on a mobile device after the calibration process is completed. Firstly, a literature review on microphone calibration, use of mobile devices as sound level meters and sound source identification is conducted. It is found that a commercially available calibrator is not designed yet for the calibration of mobile device microphones. The current methods of calibration is also investigated and it is found that the mobile device hardware, software and filters greatly affect the measurement results. The theoretical background on sound, microphones and their calibration, data acquisition and signal processing along with the sound source identification methods is also presented in the thesis briefly since these subjects become the foundation of this thesis. Various experimental setups are prepared in order to test the capabilities of mobile microphones and to investigate the shift in their performance with regards to the measurement medium. The experimental setup is carefully constructed each time before the sound measurements to make sure every equipment is ready and working. A reference condenser microphone is compared to mobile device microphones during the first two experiments for signals that are generated on computer environment and transmitted via calibrated loudspeakers.