Original URL: http://www.theregister.co.uk/2007/08/17/ft_compact_disc/

Compact Disc: 25 years old today

First commercial disc pressed on 17 August 1982

By Tony Smith

Posted in Vintage, 17th August 2007 00:54 GMT

Forgotten Tech The Compact Disc is 25 years old. Though the digital audio format's development stretches back many years before 17 August 1982, that was the date on which the world's first CD pressing plant punched out its very first disc.

CD logo

According to Philips - with Sony, the format's co-developer - the first disc off the Hanover, Germany production line was Abba's The Visitors.

While CD production commenced in August 1982, the format wasn't formally brought to market until November, and then only in Japan. US and European music lovers had to wait until March 1983 for the first discs specifically tailored for them.

Dire Straits' Brothers in Arms
Dire Straits' Brothers in Arms: all-digital

They embraced the format wholeheartedly. In the UK, Dire Straits' 1985-released Brothers in Arms was immediately snatched up by early adopters keen to put their new CD players through their paces. It was one of the first CDs produced from a digital master made from digital recordings - a so-called 'DDD' album.

But other albums proved even more popular. For many years, it was claimed record label EMI had a single CD pressing plant to producing copies of Pink Floyd's Dark Side of the Moon, such was the demand for that album. Dark Side of the Moon remains the archetypal CD album - who wants to get up and turn an LP over when you're happily getting intergalactic to the Floyd's spaced-out sounds?

The development of the CD stretches back to 1979 when Sony and Philips established an engineering team to create a disc capable of stopring music in digital form. According to Philips, the original design spec called for a 11.5cm-diameter disc capable of holding an hour's music, but this was later extended to 12cm and 74m minutes - sufficient to accomodate the whole of Beethoven's 9th Symphony. Some writers claim this was driven by Sony co-founder Akio Morita, in order to ensure his favourite symphony could be stored on a single disc.

Philips launches CD
Philips' Joop Sinjou introduces the CD in 1979

In June 1980, the development specification was frozen and enshrined in what the partners called the Red Book. Later, the arrival of the Yellow Book would see the publication of the CD-Rom specification for computer use.

It might be assumed that the CD's digital encoding is sufficient to ensure perfect fidelity. Not so. Poor laser focusing, discs that wobble as they spin introduce noise into the signal, and the inevitable dust and fingerprints that accumulate on the surface, forcing the format's developers to come up with some clever error-correction technology to compensate. Indeed, listen to a disc without the special encoding, and there's almost as much hiss as music, and arguably worse than the sound produced by cassette tape.

Pink Floyd's Dark Side of the Moon
Pink Floyd's Dark Side of the Moon: own, dedicated CD plant?

To get around the problem, CD uses a technique called eight-fourteen modulation (EFM) developed by Dutch digital recording boffin Kornelis Antonie Schouhamer Immink. The data stream is broken into blocks, each eight bits long - and half of the 16 bits used to encode the sample of the soundwave taken 44,100 times a second. The eight-bit block is matched against a list of possible bit patterns and a 14-bit code read off the table, hence eight-fourteen.

The 14-bit codes are cleverly crafted to ensure any two binary ones in the code is separated by 2-10 binary zeros. Three further bits are used to separate the 14-bit codes on the disc. While this approach may be less efficient from a storage space perspective - 17 pits on the disc's data surface are used to encode half that number of bits - it makes it much easier for the optical head to read the data correctly.

CD encoding also employs Cross-Interleaved Reed-Solomon Coding (CIRC), which adds an extra, parity byte for every three bytes of data. The upshot: the player's electronics can easily and efficiently 'guess' what data masked by errors should have been, eliminating clicks and pops.

Sony's CDP-101
Sony's CDP-101: introducing...

More advanced versions of this technique would later be used in DVD and Sony's Super Audio CD (SACD) format.

The SACD has yet to win the broad appeal enjoyed by the CD, which proved a major driver for the music industry as consumers dashed to replace old or scratched vinyl LPs and hissy cassettes with shiny new compact discs. By the late 1990s, however, in part due to the growing popularity of computer games, and first sell-through videotapes and later DVDs, but also the advent of both the MP3 music format and peer-to-peer file sharing networks, CD sales began their inevitable decline.

Sony's CDP-101
...the world's first CD player

CD remains the dominant format for legitimately purchased recorded music - some 200bn have been sold in the past 25 years, Philips reckons - but it's lead is being eaten into by downloads. Fans are finding they'd rather buy individual tracks than albums of songs. This week, the UK recording industry's Annual Survey forecast that Apple's iTunes store will outsell other music suppliers within two years - on other words, downloads will have become more popular than the CD.

Philips CD100
Philips' CD100: VHS styling

The Compact Disc may not strictly speaking be a forgotten technology, but at that rate it soon will be.

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