Spectrogram of a Dial-Up Modem Handshake Sequence

Dial-Up Modem? What the heck is that? Just kidding, of course – unless you were born in the late 90’s or later, you’ll be familiar with the sound of a dial-up modem handshake. This is the sequence of tones and noises that two remotely connected computers use to figure out each others capabilities to set the best transfer rate and settings for communicating together.

The word modem is a combination of the words modulator-demodulator. This means that the telephone signals are ‘modulated’ – or altered – with the digital data that the user is sending in such a way that the receiving computer’s modem can demodulate the received signal – ie convert it back to separate the data from the carrier signal. The handshake sounds were a way of probing each others capabilities to determine the best protocol to use to modulate and demodulate the signals. This image here is an excellent breakdown of exactly what’s happening at each stage of the process.

Thanks to Youtube User Scotty H, you can also see a video of that sequence as a spectrogram. It’s enlightening to see the specific frequencies in the sequence, and gives you a pretty good sense of the steps in the process itself as more than just random noise. Artie Ziff of the Simpsons may have gotten rich by turning dialup noises into music, but I think enough time has passed now that the noise itself can be considered musical, especially when you know what it really means!

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