Woke up, fell out of bed… rampaged by a slashdot horde.
Some clarifications to the slashdot crowd:
The whole thing was done in a couple of late nights so I didn’t really have much time to gather all the technical details concerning phonograph modulations. Moreover the "archeological" reverse-engineering aspect was part of the fun. I now know (thanks to some great replies) that the horizontal modulation (the only one I did decode) is the sum of the left/right audio channels (which are each encoded on the sides of a V-shaped groove).
Some repliers seemed to be a tad confused as to what recordings were the actual decodings. I’d like to stress that gramophone3.mp3 is a recording while the rest (dneedle*) were decoded from the image.
