An averaging method for accurately calibrating smartphone microphones for environmental noise measurement

Smartphones have become ubiquitous not only as communication devices but also as smart devices for majority of the population. The small form-factor of smartphones together with a rich set of application programming interfaces, low-power consumption, and presence of several types of sensors such as GPS, microphone, gyroscope, accelerometer, barometer etc. makes them a good candidate for building apps for measuring and monitoring various environmental parameters. However, for these apps to be useful the sensors must be first calibrated. In this paper, we focus on methodologies for accurately measuring sound pressure level and frequency spectrum using microphone built into smartphones. For this purpose, we present an averaging method for accurately calibrating a typical smartphone microphone against a reference microphone. We show experimental results illustrating that the proposed method can achieve an accuracy of ±0.7 dB for 99.7% of measurements for three Samsung smartphones. We also present results showing that it is possible to calibrate a smartphone using another smartphone calibrated using our method.