Barry Fox

A lot of what we write about is pigeon step stuff: exciting but logical progressions such as a few more megahertz or megabits, larger LCDs and cheaper Ram and Flash.

The 'tipping points', as futurologists call them, come every few years. Sometimes they are obvious, like CD and DVD.

Sometimes not; Sony's Walkman was at first written off as an expensive recorder that did not record and only worked with headphones. The hard disk personal video recorder only looked logical after Tivo.

Sometimes the big steps come because technology has caught up with an old dream. Pulse code modulation was a pre-war idea. The plan to split the country up into radio cells so that frequencies could be reused dates back to the 1940s, but no-one could make it work until the 1980s.

Spread spectrum is equally old. COFDM, the coded orthogonal frequency division multiplex system that makes digital TV and ADSL possible, began as an idea for digital radio.

I vividly remember the first time I saw the impossible: full-motion video from a music CD thanks to what later became mpeg1, and then mpeg2 and mpeg4. All these systems had to wait for huge, but cheap, processing power.

When the bugs are sorted out and new spectrum opened up, 802.11 Wi-Fi will change our lives. Given time, 3G cellular will too.

So what are the next big steps? The most likely candidates are blue laser recording, dual-layer DVD recording and hybrid DVD/CDs.

The idea of a 'hybrid' disc that works in a music CD player, CD-Rom drive, DVD-Rom drive, DVD movie player or DVD-audio player is obviously a winner - if it works. It allows single-inventory stocking, which cuts costs and customer confusion.

This is almost what the Super Audio CD (SACD) format allows. The recent Rolling Stones reissues and new Sting album were hybrids that play ordinary CD stereo on a CD player and surround audio, with higher quality, on an SACD deck.

The disc is pressed with two layers, one at the standard 1.2mm depth for CD playback and one at the 0.6mm depth used for DVD. A semi-reflective layer lets the infra-red laser in a CD player see through one layer and read the other.

An SACD player, with DVD red laser, 'knows' it should lock onto the 0.6mm layer unless 'told' to read the CD player.

This works because an SACD player is designed to play SACD hybrid discs, and SACDs are designed to play in SACD players. There is no attempt at compatibility between SACD discs and existing DVD players.

There can, however, be compatibility between SACD players and DVD video discs. Virtually all new DVD home theatre kit from Philips and Sony is based on an SACD player tailored to play either DVD video discs or SACDs.

The DVD system is bedevilled with bolt-ons. Regional coding was added at Hollywood's request. DVD recording was added late against Hollywood's wishes when the studios were too heavily committed to back out.

That's why there are several different recording formats, none of them 100 per cent compatible with existing players.

DVD-audio was an afterthought, too, and it suffers for it. An attempt at making dual-layer hybrid CD/DVDs failed miserably because playback on existing players differs from player to player. Some play the CD audio first, others play the DVD video.

That's why the five major record companies are experimenting with back-to-back CD/DVD hybrids or 'flippers' called Dualdiscs or DVD Plus discs.

A shaved-down CD, less than the standard 1.2mm thick, is glued to a shaved-down half-DVD, less than 0.6mm thick. The result is a hybrid just within the maximum 1.5mm allowed by the CD and DVD standards.

So it should not jam in slot-load players and it may or may not keep the player optics in focus, especially in high-speed Rom drives.

"They are teaching a dog to dance," said an engineer at an independent lab in the US, which has been testing hybrids sold on trial in Boston and Seattle. "The dog does dance, but it's not going to win any prizes."

Dual-layer DVD blanks work like an SACD hybrid, with a semi-reflective layer between two DVD recording layers. Not surprisingly, given the company's involvement in SACD, Philips is the prime mover.

The first recording format to get the dual-layer option and double capacity will be write-once DVD+R. Recorders and blanks are due before the end of the year. DVD-R is sure to follow.

Eraseable DVD+RW and DVD-RW are harder to modify because of the lower reflectivity of their phase-change coatings. DVD-Ram is being superseded by hard disc video.

Existing recorders will need modifying to handle dual-layer discs. The mods may involve both laser power and software control.

No-one is yet saying which of the DVD burner drives going on sale this year will be fixable. Bear this mind when buying a DVD recorder.

The third potential tipping point, blue laser recording, is coming faster than you think. A recent breakthrough in laser manufacture holds the key.

The downside is a mess of different standards that could make the VHS and Betamax fight look like a schoolyard squabble. Nothing is on sale yet - in the UK at least - so blue can wait until next month.

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