Copycode: Diminishing DAT Copycode Explained
The software encoding of CBS's aptly-named "spoiler" system consists of a very narrow 2050dB notch in the audio band centered at 3840Hz, between the musical notes B-flat and B. The copy-protection chip in the recorder measures signal energy in that band and compares it with the energy in the adjacent bands, and if it finds a large difference (indicating the presence of the notch), it shuts down the recorder. The chip has no effect at all on DAT playback, since the detection notch is not in the signal circuit, but merely runs parallel to it to feed the sensing comparator.
The system has been proven to work, but it has also been proven (contrary to CBS's claim) that the encoding has a deleterious effect on the sound, which should come as no surprise to audiophiles (see "Pure Gold" in this issue). It must have also been clear even to the densest of our legislators that DAT was not the only target of Copycode. The notch was at a low enough frequency that the system would just as effectively prevent the recording of such lower-fi encoded signal sources as analog LPs, cassettes, and eventually, radio and TV broadcasts. It could have put an end to all home taping of commercial material, leaving nothing to record except thunderstorms and baby's first belch. And if you don't think wiping out a billion-dollar industry would have a disastrous effect on our and the world's economy, think again.J. Gordon Holt