Recording industry lawyers have claimed that detailed analysis of the data in MP3 music files can prove the files were downloaded illegally from an online file-sharing network.
The revelation came with the release of court documents relating to a case against a New York woman. She is accused of sharing 1000 songs through a peer-to-peer file network, using the online pseudonym 鈥渘ycfashiongirl鈥�. She claims to have made the MP3 files found on her computer from CDs that she owned.
But lawyers for the Recording Industry Association of America (RIAA), which represents the world鈥檚 largest record companies, write in a court document: 鈥淭he source for nycfashiongirl鈥檚 sound recordings was not her own personal CDs.鈥�
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The RIAA says the username of another computer user was found in the header of one of the MP3s. Headers are routinely used to store a song鈥檚 title and length, but some MP3 compression software may also add information such as the username of the person who created the file.
The RIAA said that it also examined the digital fingerprints, or 鈥渉ashes鈥�, of the MP3s and found that some matched those of files previously see on file-sharing networks.
Markus Kuhn, a computer researcher at Cambridge University, UK, says the process of MP3 encoding involves variables that can create tell-tale differences between two files of the same song.
Sampling process
If an MP3 is copied digitally it will be identical. But making the first MP3 involves compressing the output from a CD, meaning small errors in the sampling process may produce a slightly different final pattern of bits.
Different MP3-making software programs may also compress files in a different way, producing different end results. But Kuhn points out that to his knowledge no-one has yet shown how statistically reliable using such features is in identifying the source of an MP3.
MP3 compression reduces the size of CD digital music files by 90 per cent. This has made it possible to send music over the internet quickly and store thousands of music files on a computer hard drive. The loss in listening quality of the music is minimised by removing sounds in the original file that are calculated to be inaudible to the human ear.
The music industry has been granted more than 1300 US court subpoenas forcing ISPs to reveal the identity of users offering files for download through peer-to-peer networks. Those found guilty could face fines of between $750 and $150,000 for each song.