Digital watermark

The solution for a piracy and duplication protection scheme developed jointly by Sony and Philips which writes copyright data encrypted within the CD/DVD etc. disc itself. This scheme would, for example, encode discs with a country code so that these discs would only play on players from the same country. This is presumably better than older forms of digital copy protection which tried various pilot tones or random number generators, failing ultimately because the results were either too audible or too easy to circumvent. In a digital watermark, the copyright data are stored as a modulation of the width of the injection-molded pits. Duplicating the watermark would require the same equipment as that which produced the disc stamper, the distribution of which is presumably tightly controlled. It is also possible to synchronize the modulation of the pit widths so that there is a visible pattern formed on the disc pit substrate itself, making an “analog” watermark (without the need for water, of course.) In addition to the watermark and country codes, identifiers for the mastering house and pressing plant, glass master number, ISRC catalog numbers, etc. can be stored. The digital watermarking technology has been called Pit Signal Processing (PSP) which works by modulating the strength of the laser used to record the digital data onto the glass master. One by-product of the watermarking process is that the EFM used to encode audio data onto the CD master allows the pits to vary in length between 3-11 units. These slight errors in length, or “jitter” result in slight timing errors which can cause a smearing of the stereo image as well as an increase in HF noise. The more rigid requirements of pit length control in watermarking should result in a significant reduction of pressing-induced jitter, just generally improving the CD production process.

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