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Microsoft wants to nail online music outfits (who could they mean?) who
“encourage illegal distribution of copies of copyrighted material”. So Bill
Gates’s crew have developed a music copy-control system which, in the overblown
prose of WO 01/06755 “brings one to the gates of the city of El Dorado where an
encoded watermark is unalterable and irremovable”—and, one hopes,
inaudible. Microsoft buries copyright codes in the music by slightly increasing
and decreasing the level of selected frequencies. To stop pirates snatching
clips, the same coded message is repeated every few seconds—but changed
each time in a secret, predetermined way. Microsoft’s detector uses the same
sequence to read each code.