Dial-up internet involves converting bits into sound (both in audible and ultrasonic spectrums) and then back on the other end of a phone line. The Google Tone

Dial-up internet involves converting bits into sound (both in audible and ultrasonic spectrums) and then back on the other end of a phone line. The Google Tone extension (http://googleresearch.blogspot.com/2015/05/tone-experimental-chrome-extension-for.html http://googleresearch.blogspot.com/2015/05/tone-experimental...) uses both ultrasonic sound and an audible DTMF-based codec. Audio tones are also used for setting up Google OnHub routers; the router emits a tone and the Google On setup app listens for it. (https://support.google.com/onhub/answer/6246481?hl=en https://support.google.com/onhub/answer/6246481?hl=en)