Decoding acoustic tone from vibrating paper using a smartphone

The availability of low-cost cameras and the development of computer-vision methods have driven the demand of vision-based technology in real-world applications. In this study, we examine the effect of sound on a thin sheet of paper placed 5 cm away from the sound source (speaker). Tiny movements on the paper induced due to the sound generated using speaker were recorded in the video. The slow-motion feature of the smartphone camera is used to observe the sound vibrations. The video was recorded at rate of approximately 240 frames per second and pure tone with frequency varying from 50 Hz to 110 Hz has been detected on the piece of paper. A computer vision method employing Harris-corner detection technique is used to detect the feature movement caused with respect to the sound played. It also opens the possibility of finding the frequency of the noise generated due to nearby sound sources by observing the movements on the membrane, curtains, plant leaves, etc. Further it serves as a basis to work in the direction of extracting the sound information using the vision technique employing simple smartphone.