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.
There are three sets of songs provided here. The first two zip files contain "songs" that decode to English, and a set that decode to Chinese. These songs are simpler to decode; they were recorded by a jazz singer, Susan DeJong, and pianist Michael Bell. The songs in the first file decodes to English phrases, and the second one to Chinese phrases. The songs are currently available from the following two links, although this location is likely to change soon:
To decode the songs, transcribe a 1 for each high note, and a 0 for each low note. The notes (bits) are in groups of 5, which should be translated to a decimal number. For the English messages, 1 decodes to A, 2 to B, and so on. For Chinese, the numbers 1 to 4 represent tones 1 to 4, then 5 is A, 6 is B, and so on. For more details, see the PDF file in the box on the right.
The major challenge is in the video "Reaching out" (below, and available for download from vimeo.com/23952295), which contains over 20 hidden binary message in total. The main message can be decoded by noting the pitches of the main tune as for the previous songs (which leads to a reward for diligent students); but there are over 20 messages coded in different parts of the video, including the other instrumental parts, background images, and the dancing.
The names of the first few people to decode various parts of the music video will be posted here; the hidden messages in the song tell you how to get your name here!
The very first correct decoding was completed by a family team effort: The Engelberg Family (Mark, Alex, Mindy and Molly) from Everett, Washington, USA. In addition to decoding the messages to get to the hall of fame, they found 7 additional hidden messages in the song. Congratulations!
Phil Tulga has a musical activity coding words as morse, and then writing music with it. Morse uses the idea from information theory that more probable symbols should have shorter codes, so there's computer science in that too!
The Wikipedia entry on modems provides details on how more conventional modems work: http://en.wikipedia.org/wiki/Modem
Bacon's cipher uses a very similar principle, where 5-bit codes are hidden in a text, usually by changing the typography of the letters instead of using high and low notes.
Vi Hart has written music using binary numbers as the basis for the rhythm.