Researchers at Princeton University conducted massive privacy survey and found Google tracking users on nearly 80 percent of all Top 1 Million Domains using various tracking and identification techniques. The new technique is based on fingerprinting a machine’s audio stack through the AudioContext API. The technique is not collecting audio played or recorded on a machine, but rather harvesting the audio signals of the each machine that is then using it to reveal unique browser and device combinations. Google, Facebook, Twitter and Google are the only third-party entities present on more than 10 percent of sites.
Source: https://thehackernews.com/2016/05/audio-fingerprint.html