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Silent safeguard

发布时间:2019-03-07 08:15:01来源:未知点击:

By Barry Fox RECORD companies believe they have finally found a technology they can use to “watermark” music recordings to control copying from the Internet and from the next generation of digital CDs. They say the listener will not be able to hear the watermark signal, hidden in their music. The companies’ joint anti-piracy consortium—the Secure Digital Music Initiative (SDMI)—has tested all the competing systems and chosen what many regard as a “dark horse”, the MusiCode system from Aris Technologies of Cambridge, Massachusetts. In a further boost for the system, it was also chosen last week to control copying on the new DVD-Audio system, which is due for launch later this year. The SDMI was formed last year when the Recording Industry Association of America failed in a legal bid to block sales of Rio, an Internet music recorder that uses MP3 compression technology to download music from the Internet. The 120 companies now in the SDMI decided that music should be watermarked at the recording studio to identify the copyright owner and specify how the music could be sold—on a CD, for example. An “SDMI-compliant” Internet music player will search for any mark revealing that a recording is an unauthorised copy from the Internet, and refuse to play it. The mark must survive conversion between analogue and digital formats and resist hackers who may try to remove it, while not degrading the sound. Some spread a thin layer of coded noise under the audio, while others subtract tiny frequency bands from the music and add code-containing noise to the gaps. The Aris encoder holds a library of alphanumeric symbols, represented by predetermined patterns of a musical waveform, such as peaks at defined levels occurring within a fixed period of time. The encoder analyses the music, looking for patterns that are similar to the library patterns. When a near match is found, the encoder modifies the music slightly so that it exactly matches the symbol pattern. A decoder in the player looks for the same symbol patterns in the music and uses them to recreate the copyright message. The record companies played marked and unmarked music in their studios to panels of audio experts with particularly finely tuned hearing—so called “golden ears”. Recording engineer Bob Ludwig warned earlier this year that although watermarking might be inaudible on low-fi Internet music, its effect on super hi-fi DVD-Audio would be noticeable. Ludwig, who has engineered recordings by artists like Bruce Springsteen and Pearl Jam, was initially hostile to watermarking because he had never heard a system that did not affect the sound. He now says: