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CD DVD Duo Disc
Duo DiscDuo Disc or Dual Disc 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 5.1 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 strict 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 10 Dual layer Double Sided discs.

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DualDiscs first manufactured 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

How a DualDisc worksDualDiscs appear to be based on double-sided DVD technology such as DVD-10, DVD-14 and DVD-18 except that Dual Disc 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 Dual Disc 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.

CD ReplicationBecause 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.

Because the DualDisc CD layer does not conform to Red Book specifications, Philips and Sony have refused to allow DualDisc titles to carry the CD logo and most DualDiscs contain one of two warnings:

"This disc is intended to play on standard DVD and CD players.
May not play on certain car, slot load players and mega-disc changers."
"The audio side of this disc does not conform to CD specifications and therefore not all DVD and CD players will play the audio side of this disc."
The DVD side of a DualDisc completely conforms to the specifications set forth by the DVD Forum and DualDiscs have been cleared to use the DVD logo.


Hopes for Duo Disc / Dual Disc

Record companies have two main hopes for Dual Discs; the first being that they will eventually replace CDs as the preferred media for purchase at music retailers, and the second being that the inclusion of bonus DVD content at a price similar to a conventional CD will help to slow down online music piracy by giving consumers more incentive to buy their music through retailers. Some titles such as Devils & Dust by Bruce Springsteen and Straight Outta Lynwood by "Weird Al" Yankovic have been released in the United States on DualDisc only.

Costs versus conventional CDs

In the US, the cost of a DualDisc at retail versus that of a conventional CD varies depending on the title but, on average, a DualDisc costs about $1.50 to $2.50 USD more than the same title on CD. Some Dual Disc titles such as In Your Honor by the Foo Fighters have enhanced packaging which increases the retail cost of the DualDisc version of the albums over their CD counterparts more than the average. There are also other factors which go into the additional costs such as production, marketing etc.


Common DVD content

What one finds on the DVD side of a DualDisc title will vary. Common content includes:

The entire reprinted album in higher-quality stereophonic and/or surround sound.
Documentaries
Music videos
The artist's discography
A link to the artist's website
There are sometimes film-and-soundtrack DualDiscs.

Audio types

The CD side of a DualDisc contains standard 16-bit LPCM audio sampled at 44.1 kHz. On the DVD side, most record companies, with the notable exception of Sony Music, provide the album's music in both high-resolution, 24-bit DVD-Audio (typically at a sample rate of 96 or 192 kHz for stereo and 48 or 96 kHz for surround sound) and lower-resolution, 16-bit Dolby Digital sound (typically sampled at 48 kHz). This is done to allow consumers with DVD-Audio players access to very high-resolution stereophonic and/or surround sound versions of the album while also providing the lower-resolution Dolby Digital stereophonic and/or surround sound which is compatible with any DVD player.

Because Sony has a high-resolution audio format, SACD, (Super Audio CD)in the marketplace which directly competes with DVD-Audio, Sony Music, as a general rule, only provides 16-bit, 48 kHz sampled LPCM stereophonic (and sometimes Dolby Digital Surround) sound on the DVD side of their DualDiscs. The sound is compatible with any DVD player; however, it does not provide the higher fidelity and resolution of 24-bit, high sample-rate DVD-Audio.

Competition

Super Audio CDHow a hybrid Super Audio CD works. The biggest competition to DualDisc is the hybrid Super Audio CD (SACD), which was developed by Sony and Philips Electronics, the same companies that created the CD. DualDiscs and hybrid SACDs are competing solutions to the problem of providing higher-resolution audio on a disc that can still be played on conventional CD players.

DualDiscs take the approach of using a double-sided disc to provide the necessary backwards compatibility; hybrid SACDs are a one-sided solution that instead use two layers: a conventional CD layer and a high-resolution layer.

Lasers in conventional CD players have a different wavelength (typically around 780 nm) than those in SACD players (650 nm). Hybrid SACDs possess a special high density layer that is transparent to the conventional CD player's laser but is partially reflected by the SACD player's laser. When a hybrid SACD is placed into a conventional CD player, the laser beam passes through the high-resolution layer and is reflected by the conventional layer at the regular 1.2 mm distance. The result is that the hybrid disc plays as normal.

When a hybrid disc is placed into an SACD player, the laser is partially reflected by the high-resolution layer (at 0.6 mm distance) before it can reach the conventional layer. If a conventional CD is placed into an SACD player, the laser will read the disc without incident since there is no high-resolution layer to reflect. Because of the difference between the working distances of CDs and SACDs, the aperture of the lens in the SACD player must be adjusted to obtain the correct focal length.

Hybrid SACDs claim a higher compatibility rate with conventional CD players than DualDisc, due to the fact that hybrid SACDs conform to Red Book standards. However, a SACD or SACD-capable DVD player is required to take advantage of the enhanced SACD layer. With a DualDisc, consumers can use their existing DVD player to hear surround mixes. (DVD-Audio capable players are required for higher-resolution audio, if present.) It is currently estimated that 75% of households in the United States have at least one DVD player.

In addition, several SonyBMG titles whose regular editions include copy protection programs (such as XCP and SunnComm) do not feature the software on the DualDisc versions.

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