If you’ve ever wondered exactly what was going on with a modem…
You can actually buy a poster of the spectrograph (https://oona.windytan.com/posters/dialup-final.png) - if you want to send a fun gift to someone who grew up in the BBS era.
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That’s awesome. And apparently there’s a 20 char post minimum. So here’s more than 20 chars in total. 
I just think the idea of transferring digital data over an audio link is so cool! Hearing all the different PSK, FSK, QSK, etc. types of modulation running digital ham modes is fun.
For a little bit anyway. Some of them are pretty fingernails-on-blackboard annoying after a short time.