A study of online trackers carried out by researchers at Princeton University allowed the identification of the Audio fingerprinting tracking technique. A group of researchers from the Princeton University have conducted a study on multiple Google domains and discovered the company is tracking users on nearly 80 percent of all Top 1 Million Domains. The technique is devious as efficient, a third-party tracker could use the AudioContext API to send low-frequency sounds to a users machine and then measures the way it processes the data in order to create a unique fingerprint.”]
Source: http://securityaffairs.co/wordpress/47550/digital-id/audio-fingerprinting-tracking.html