Event-Based Visual Microphone Using Laser Speckle

Ryo Shirakawa, Shiori Sugimoto, Yoko Sogabe, Shoichiro Saito, Masaki Kitahara

Abstract: Since sound causes minute vibrations in objects surrounding the sound source, Visual Vibrometer allows us to recover the sound from remote point by optically measuring the vibration on the object's surface. For that system, Laser Doppler Velocimeters (LDVs) and high-speed cameras are commonly used, but there are issues in terms of equipment cost and data efficiency. Therefore, a technique has recently emerged to use event-based cameras in place of such equipment. Event-based cameras record only changes in brightness, independently, at each pixel, and its advantages such as high temporal resolution, high data efficiency, and simple device structure make it easier to measure. However, the technique is highly dependent on the object's surface characteristics, so the measurement conditions can prove difficult to realize. In this paper, we propose a new measurement system that observes changes in laser speckles caused by vibration using an event-based camera to achieve more robust measurement conditions, and a method for recovering sound from the event signals. The proposed sound recovery algorithm recovers the audio signal by noise reduction, sign assignment, and integration, assuming that the number of events produced by speckle pattern shift and detected at each time is closely related to the absolute value of the vibration speed. This method is very simple yet effective, and its performance is demonstrated by experiments in real environments.

External IDs:dblp:conf/eusipco/ShirakawaSSSK25