Sounding out pirates

By Barry Fox
March 22, 2005

How would you react if the voice of a record-company boss boomed through your speakers and berated you for pirating music?

You may find out, if the music industry decides to adopt an invention by Mark Bocko and Zeljko Ignjatovic.

With help from the US Air Force Research Laboratory, the New York inventors found they could bury about 20 kilobits of speech data in a song without affecting how it sounds.

Their technique exploits the fact that the tones of a musical instrument are made up of a complex pattern of randomly phased harmonics. By forcing a few of these harmonics to move in and out of phase with a chosen reference, they can be made to convey a digital message.

These phase shifts are so small they are imperceptible to the ear. But a software decoder, which could be built into MP3 players or file-sharing applications, detects the phase shifts and turns them into speech.

New Scientist


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