Ip over sound

If you ever connected to the Internet before the 2000s, you probably remember that it made a peculiar sound. But despite becoming so familiar, it remained a mystery for most of us. What do these sounds mean?

In order to measure the doppler effect for motion detection on a conventional computer, what you can do is send out a sinusoid at some known (inaudible) frequency, say, 20 kHz. If something is moving in the room, then, after the sinusoid has bounced around on the walls and into the microphone, the sound will shift in frequency. This can be measured by looking at the frequency spectrum in the nearby region of the 20 kHz tone.

arecord -f cd | ssh -C user@host aplay -f cd

or the other way around

ssh -C user@host arecord -f cd | aplay -f cd