This activity involves listening to songs and finding hidden messages based on the same principle as a modem.
The binary number activity briefly mentions how text could be coded using sound — high and low beeps represent binary digits, which in turn can be decoded to numbers that represent the letters of the alphabet.
All data on computers is stored and transmitted using the binary number system. When the binary digits need to be sent over phone lines which used to be standard in home internet connections, the digits are converted to sound and decoded at the other end, using a modem. This activity uses an audio coding similar to that used by a modem, but the sounds are recorded as songs, which students can decode.