The sound of a dialup modem, pictured

Communication protocol of a dialup handshake depicted with a spectrogram.

cross-posted from: https://sh.itjust.works/post/500500

cross-posted from: https://sh.itjust.works/post/319324

Source: https://www.windytan.com/2012/11/the-sound-of-dialup-pictured.html?m=1