The first five or so years of Compact Disc's life saw a struggle to establish the format as the world's universal new music medium, and a specifications war that involved ever more elaborate variations on the theme of 16-bit, 4-times oversampling DACs. But suddenly, in 1989, Pulse Density Modulation (PDM) – or Bitstream to its friends – arrived, ending the numbers war. It was a very different system of converting the digital audio stream to analogue, one which meant the end of multi-bit DAC chips. This new system used just one bit, crunched at very high speeds, taking the oversampling and noise-shaping process to the limit. Each 1-bit pulse was oversampled 256 times.

There were clever technical reasons for doing things this way – ones that are relevant even today in the debate about PCM vs. DSD – but one key practical benefit was that Bitstream DACs were and are cheaper to make. When chips are manufactured in their millions, to fit into a vast range of devices from cars to mobile phones, that represents a huge cost saving. Also, 1-bit DACs use less power, making them better suited to portable use. For these reasons alone, Bitstream (and variations on the theme) was always going to take over, and transform the digital audio landscape.

Philips referred to its new 1-bit digital converter as 'DAC3' internally, but gave it an official designation of SAA7321. It packed some very clever digital signal processing, the result being that it output a signal with the full 96dB dynamic range of CD but was much more linear than the multi-bit designs it replaced. It was treated with great respect by the audio press, and there was a clear feeling that the days of conventional multi-bit DACs were numbered – just a year or so after its 1989 launch, it was beginning to get hard to buy a new multi-bit machine!

Bitstream effectively ended the debate about DACs; most modern off-the-shelf designs today are variations of this 1-bit design. It made CD players cheaper and in the lower end of the market at least, easier to listen to. Distortion levels came down, and the format's upper midrange hardness – or even 'shrillness' – largely disappeared. And it paved the way for a coding system that used one bit samples working at a giddy 2.8224MHz. Direct Stream Digital (DSD) delivered a 20Hz to 100kHz frequency response and around 120dB of dynamic range. This system was adopted for the SACD format that was to arrive ten years later, but by the mid-nineties, Sony Music was archiving its back catalogue using it. 

DIGITAL CHALLENGERS

In the nineties, Compact Disc began to lose some of its momentum. Machines got slicker and better made – especially at the high end – and more attention was paid to low jitter master clocks too. Yet the frenzy of CD hardware development seen in the eighties had gone, as Sony put its time and money behind its new MiniDisc (MD) format, and Philips and Matsushita Electric launched Digital Compact Cassette (DCC), both on sale towards the end of 1992. These were variations on the 16-bit, 44.1kHz PCM theme, albeit with dramatically less storage capacity, which was made up for by clever data reduction systems – using psychoacoustics to decide which bits of the digital waveform the human ear couldn't hear, and – in effect – what to throw away. MD's ATRAC system and DCC's PASC (Precision Adaptive Sub-band Coding) were basically variations on what would later become MP3, and came from its predecessor MPEG-1 Audio Layer I.

The first serious attempt to improve on CD was in 1995, with the advent of High Definition Compatible Digital (HDCD) from Pacific Microsonics. This wasn't a new standard as such, but a clever tweaking of the existing one. HDCD discs could be played back on standard CD players, but when used in HDCD players and DACs would give a claimed 20-bit resolution by using custom dithering, audio filters, and some reversible amplitude and gain encoding. The system worked surprisingly effectively, giving a smoother, more powerful, dynamic sound. Over 5,000 titles were released, but HDCD simply didn't catch on for the same reasons that the audiophile formats that followed, failed…

One could argue that CD's last hurrah was Super Audio Compact Disc – the official, spiritual successor to Compact Disc. It arrived in 2001 and was a brave and imaginative attempt to address the sonic weaknesses of the original silver disc. Jointly developed by Philips and Sony, it used the (then) new Dual Disc technology to provide a music disc that was playable in CD format on CD players, but when inserted in SACD players, would read the deeper SACD layer on the disc, via a second 650nM laser pickup. This high-density layer contained up to 7.95GB of data, compared to less than a tenth of this on CD. 

SACD used DSD coding and gave very pleasing sonic results – even when compared to another rival DVD-based high-end audio format, DVD-Audio. The latter wasn't compatible with standard CD players and was more fiddly to use – requiring the use of a monitor display. Its maximum permissible 24-bit, 192kHz PCM audio stream didn't sound any better than SACD; indeed, many thought it worse. Neither of these formats dealt CD a death blow because the public was simply unwilling to invest in new disc formats when Compact Disc suited them just fine. The same could be said for the retailers; in physical 'record shops' it didn't make sense to take up valuable shelf space with a far more expensive disc that most people couldn't or didn't want to play, anyway!

Instead, the beginning of the end of Compact Disc came from MPEG-1 Audio Layer III, or MP3, to its friends. This was the first time for consumers that a digital audio format was divorced from its storage medium. MP3 was basically a file format that could be stored on any computer memory device and played back from a computer. The format took off because of the rise of Napster, a peer-to-peer music file-sharing website that allowed anyone with a modem to download music for free (or at least, for the cost of the time on the telephone line, in those pre-broadband days). 

Peer-to-peer music files flourished around the turn of the millennium but began to flounder as the music business attempted to wrest control back from so-called music 'piracy'. Still, the idea that you no longer had to pay for music, or indeed CD players, stuck around with many, and that was the very early beginnings of the CD's demise. Apple then moved in for the kill, launching iTunes, the iPlayer, and then the iTunes Music Store – where people, in effect, bought their music in compressed AAC format. It soared in popularity, and Compact Disc suddenly seemed very old hat. This, in turn, began the transition to streaming as we know it today.

FOREVER CHANGES

For most of the first decade of the new millennium, DVD-Audio and SACD achieved some limited success in the international audio community; indeed, the latter was actually very popular in Japan, and remains so to this day. But just as MP3-quality music effectively migrated off a physical format – i.e. from MD and DCC – so CD-quality music would follow. Various streaming services like TIDAL began to appear, initially offering compressed downloads or streaming options. Initially, they were misleadingly described as 'CD quality', but it later became practical to stream in actual, real CD quality rather than compressed. A few years later, the same happened for hi-res music. Audiophiles had become used to downloading them from websites such as HD Masters, but by the end of the noughties, hi-res streaming was becoming a thing. Companies such as Qobuz set their store by it, and began to pressure other more established streaming services to offer hi-res too.

In the USA, which is a good gauge of consumer behaviour in the Western World, CD sales began their decline in 2004, where nearly a billion discs were sold. Since then, yearly industry data has shown Compact Disc sales dropping slowly by volume and profit, down to a point in 2020 when just 31.6 million were purchased by music fans. At the same time, there has been a suitably dramatic uptick in streaming – so much so that industry watchers have been predicting the end of the road for silver discs over the past few years. Fascinatingly though, in 2021 CD sales increased slightly, according to US industry trade body, Recording Industry Association of America. CD shipments actually rose from 31.6 million in 2020 to 46.6 million that year 2021, which is a not inconsiderable jump of 47 per cent. Revenue also rose from $483.2 million to $584.2 million. 

Although quite surprising, it seems 'the death of physical media' is not quite with us then. Like the vinyl LP, sales of which have been slowly growing since 2005, it appears that not everyone is willing to give up Compact Discs quite yet. That's not to say that streaming isn't absolutely dominant; paid subscriptions to services account for nearly sixty percent of music revenue, taking in nearly $10 billion. By contrast, LP and CD form less than eleven percent of music industry income.

Despite the novelty appeal of having a massive music collection available to you at the swipe of an app, many people still like physical formats – and both LP and CD are, in their respective ways, pleasing to use and to own. CD is what it's always been – convenient; there's no messing around with wireless networks, and if you already own CDs, you don't have to pay again to hear them, unlike streaming. Better still, the artists get a fair slice of the pie. There are horror stories in the USA, UK and elsewhere about well-known musicians only getting tiny amounts of money per stream. That's why many of them make most of their money from touring now or selling their wares on CDs they've had made for themselves – bypassing the record company.

Sonically too, Compact Disc still has much to give. Much of the early criticisms of the format were down to the mastering of the discs themselves. CD showed up the miking techniques of the seventies, which had been designed around the slight compression that analogue systems give. With digital, they sounded harsh, upfront and shouty, whereas with analogue, the end result was better balanced. Ken Ishiwata pointed out to me that “the mastering equipment in that period was poor, but the recordings were bad too – many people didn't know how to make good digital recordings”. Ivor Tiefenbrun added that “there were so many flaws in the process that in a way it was a shame to judge CD by the early releases… it took about ten or fifteen years before the recording engineers and others engaged in the process learned how to make the best of this format despite its limitations and critical lack of headroom and precision.”

Modern DACs can make a very good fist of CD's relatively modest (by today's standards) 16-bit, 44.1kHz digital specification, and it's certainly a fallacy that any hi-res file played on anything sounds better than CD being played on a decent CD player. At the time of the release of DVD-Audio and SACD, I remember making direct comparisons with my high-end CD player playing CD, against the (then) best DVD-A and SACD machines playing the same recordings in their respective formats – and it didn't always go against CD. 

With good mid-price (or higher) DACs, excellent sound can be had from CD transports into modern DACs. The limiting factor is more likely to be the amplifier or loudspeakers than the resolution of the digital audio file. Also, many people now agree that CD transports sound better than streamed Red Book CD-quality music via streamers; such are the issues that the latter face in making the best from the digital datastream. 

AND IN THE END

On the occasion of its thirtieth anniversary, ten years ago, Ken Ishiwata told me that “CD will be in the household for a great many more years to come”, and he has been proven right. In a world of multiple music formats, many now being non-physical, Compact Disc still has a place for many people. This is down to exactly the same virtues that the format showed forty years ago – sound quality, convenience, and ease of use. And now, in its fortieth anniversary year, we can see it clearly for what it is – a technological tour de force at the time of its launch, something that brought cutting-edge tech to a vast audience of music lovers worldwide. And with its slight uptick in sales, for this little silver disc, a new life could begin at forty?

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