Optical microphone can separate multiple instruments from afar

Researchers at Carnegie Mellon University have presented some remarkable audio from a new optical microphone system that uses cameras to see and reconstruct sonic vibrations. Here's the basic theory: sound is nothing but a series of pressure waves that travel through the air. An optical microphone is basically a camera system designed to monitor and interpret vibrations on the surface of a sound source - or even objects placed near a sound source, which vibrate in sympathy with the sound waves in the air around them. The Carnegie Mellon team's system shines a laser on the vibrating surface, creating a precise speckle pattern that distorts as the sound source vibrates. This optical mic can read sound up to a remarkable 63,000 Hz thanks to some very clever use of the cameras involved. "We've invented a new way to see sound," said Mark Sheinin, lead author on the research paper and a post-doctoral research associate at the Illumination and Imaging Laboratory in Carnegie Mellon's Robotics Institute. The team has tested this optical mic on guitar and violin, on a speaker cone, on tuning forks, and even on a Doritos bag sitting in front of a speaker and vibrating in sympathy with the ambient sound.