Hybrid DVD-CD Fails to Impress in Tests

An attempt to create the Holy Grail of home entertainment - a disc that plays on any DVD or CD player - has been branded a failure by an international working group. Music and movie buffs currently have to choose between CD for stereo music, DVD-Video for full-length movies with digitally compressed surround sound, and DVD-Audio with uncompromised surround sound, plus short video clips.

In an attempt to produce one disc that does it all, experimental Multi Format hybrid discs were pressed by Warner. The discs have a CD layer of the usual thickness, 1.2 millimetres, and a DVD layer halfway down at 0.6 mm. The two layers are separated by a semi-reflective film, which lets infra-red laser light through to the CD layer but reflects the red laser light used to read DVDs.

The Multi Format discs were tested by a consortium of fifteen members of the DVD Forum, including JVC, Panasonic, Pioneer, Sony, and Toshiba. They used 49 different DVD-Audio players and 133 DVD-Video players.

However, an internal report from the DVD Forum's Working Group 4 has now "unanimously agreed" that the discs "cannot be played properly" by existing players and would cause "severe confusion in the market".

CD Confusion
The problem is that existing DVD players, which are designed to play both DVDs and CDs, get confused when faced with the hybrid disc. Half the DVD-Audio players used in the tests incorrectly played the Multi Format discs as simple CDs, and a quarter of them either refused to play at all or gave random results. And nearly two-thirds of the DVD-Video players incorrectly played the hybrids as CDs; and a fifth of the players refused or worked randomly.

Panasonic spokesman Peter Weber acknowledges the problems shown up by the tests. But has said, "It is premature to say that plans for a hybrid are dead. Work is continuing on other solutions."

The collaborating companies are now trying a different kind of hybrid, which bonds two different discs back-to-back. This gives a double-sided disc with a CD layer on one side and a DVD layer on the other.

However, this creates a different problem. The CD and DVD standards set a thickness tolerance of -0.1 mm and +0.3 mm, meaning the double-sided disc may be too thick to fit in some players. Making the layers thinner might appear to be a solution, but this can spoil playback as the transparent part of the disc plays a role in focusing the laser that reads the data.

The DVD manufacturers have very good reason to continue their quest for a hybrid disc. Super quality, surround sound is already available on Super Audio CD hybrid discs, which play in stereo on a CD player. The format was developed by Philips and Sony and has been successful - the Remastered Rolling Stones CDs, which have sold 1.5m so far, use SACD technology.

But the surround sound can only be heard when the disc is played on a new SACD player. A hybrid DVD/CD disc would mean super-quality sound could be generated by a DVD player.