5 Disc Changers

DualDisc is a type of double-sided optical disc product developed by a group of record companies including EMI Music, Universal Music Group, Sony/BMG Music Entertainment, Warner Music Group, and 5. more...

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1 Entertainment Group and now under the aegis of the Recording Industry Association of America (RIAA). It features an audio layer similar to a CD (but not following the Red Book CD Specifications) on one side and a standard DVD layer on the other. In this respect it is similar to, but distinct from, the DVD Plus invented in Europe by Dieter Dierks and covered by European patents.

DualDiscs first appeared in the United States in March 2004 as part of a marketing test conducted by the same five record companies who developed the product. The test involved thirteen titles being released to a limited number of retailers in the Boston, Massachusetts, and Seattle, Washington, markets. The test marketing was seen as a success after 82% of respondents to a survey (which was included with the test titles) said that DualDiscs met or exceeded their expectations. In addition, 90% of respondents said that they would recommend DualDisc to a friend .

DualDisc titles received a mass rollout to retailers throughout the United States in February, 2005, though some titles were available as early as November, 2004. The recording industry had nearly 200 DualDisc titles available by the end of 2005 and over 2,000,000 units had been sold by the middle of that year. .

Technical details

DualDiscs appear to be based on double-sided DVD technology such as DVD-10, DVD-14 and DVD-18 except that DualDisc technology replaces one of the DVD sides with a CD. The discs are made by fusing together a standard 0.6 mm-thick DVD layer (4.7-gigabyte storage capacity) to a 0.9 mm-thick CD layer (60-minute or 525-megabyte storage capacity), resulting in a 1.5 mm-thick double-sided hybrid disc that contains CD content on one side and DVD content on the other.

The challenge for the designers of DualDisc was to produce a dual-sided disc which was not too thick to play reliably in slot-loading drives, while the CD side was not too thin to be tracked easily by the laser. DVD Plus, though conceptually similar, uses a thicker CD layer and thus is more likely to get stuck in a slot-loading player (although this appears to be almost unknown); DualDisc takes the other course by thinning the CD layer.

Because the 0.9 mm thickness of the DualDisc CD layer does not conform to Red Book CD Specifications, which call for a layer no less than 1.1 mm thick, some CD players may not be able to play the CD side of a DualDisc due to a phenomenon called spherical aberration. As a result, the laser reading the CD side might get a "blurry" picture of the data on the disc; the equivalent of a human reading a book with glasses of the wrong strength. Engineers have tried to get around this by making the pits in the CD layer larger than on a conventional CD. This makes the CD side easier for the laser to read; equivalent to the book using bigger print to make it easier to see, even if the person's glasses are of the wrong strength. The downside to this, however, is that the playing time for the CD layer of some early DualDiscs decreased, from the standard 74 minutes of a conventional CD, to around 60 minutes, although this early limitation now appears to have been overcome.

Read more at Wikipedia.org