The introduction of the compact disc was the greatest single leap forward in the history of recorded audio after Edison’s invention of the phonograph in 1877 and the introduction of electrical recording in the late 1920s. By 1983 the long-playing (LP) record had entered what the late Peter Mitchell, my prime audio mentor, aptly referred to as its Baroque period. All the “improvements” that were then being touted — linear-tracking turntables, moving-coil phono cartridges, and dynamically compressed recordings designed to be expanded on playback by dbx or CX decoders — were merely ornamentation on the technologically ancient stylus-in-groove structure. Something had to kick the music industry out of its noisy, skip-prone vinyl groove.
Experiments with digital audio recording had been going on for years at, among other places, the BBC, Denon, Sony, and, in this country, Thomas Stockham’s enormously influential Soundstream company. A marriage between digital audio recording and Philips’s optically based, but basically analog, laserdisc system — with its damage-resistant, wear-free medium — seemed promising. Years of research, development, and wrangling over standards (I attended some of the committee meetings) culminated for me in the December 1982 issue of Stereo Review, our predecessor, which contained an advance look at Sony’s first CD player, the CDP-101. I had the privilege of writing that article, the first in-depth review of a CD player in an American publication, which appeared several months before it or any other CD player actually went on sale in this country. That didn’t happen until March 1983, which is why we’re celebrating the CD’s 20th anniversary this year and not in 2002.
Aside from its sound quality, much of my excitement with the new CD medium came from the high technology required to bring it to market. The new players featured the first consumer applications of such technologies as:• Semiconductor lasers.
The CD wasn’t the first consumer product containing a laser — that honor belongs to the laserdisc system, which used gas-filled helium-neon laser tubes. But CD players were the first products to exploit the then ultra-high-tech solid-state semiconductor laser. (The lasers were so high-tech that it was said CD players had export restrictions to prevent the lasers from “falling into the wrong hands.”) Emitting an invisible near-infrared beam, the new lasers consumed far less power than gas lasers, were much more compact, immune to physical abuse and misalignment, and lasted far longer (the laser in my 20-year-old CDP-101 still works, even if little else in the player does). Without solid-state lasers, portable CD players and CD boomboxes would be impractical. Red-beam semiconductor lasers are now at the heart of the DVD system and its portable players, and devices emitting even shorter-wavelength blue beams are the core technology for the upcoming high-definition DVD systems.
• Linear PCM audio data encoding.
The CD format, of course, was the first to employ digital audio and its mathematical framework, which includes such things as the absolutely fundamental “sampling theorem.” There was a lot of debate as to how digital audio should be encoded — essentially, the type of number to be recorded. In the end, the most computer-friendly format was selected: linear pulse-code modulation (PCM), in which the voltage of an analog signal is divided into evenly spaced (“linear”) steps, each of which is assigned a binary number (the “pulse code”). The CD pulse code is composed of 16 binary bits, allowing 216 data steps and decimal-equivalent numbers running from –32,768 to +32,767.
Developments in the following decades have shown the wisdom of choosing linear PCM. It greatly simplifies any digital signal processing (DSP) that must be performed on the audio. For example, the digital equalizers and ambience-enhancement systems now found in advanced A/V receivers all manipulate audio in PCM form. DVD-Audio also uses PCM, but with a maximum of 24 bits of resolution (224 data steps running from –8,388,608 to +8,388,607). Single-bit encoding systems, such as the Direct Stream Digital data format employed for Super Audio CDs, do not have an easy affinity for traditional DSP, a factor that has hampered the development of such things as bass management and speaker-distance compensation in SACD players.
• A 12-centimeter polycarbonate disc substrate.
Philips initially proposed that the CD be a smaller disc with maybe 45 minutes playing time. But legend has it that the late Akio Morita, then head of Sony, marched into its R&D department one day and “requested” that the new system be able to hold a complete performance of Beethoven’s Ninth Symphony, which usually runs more than an hour and is extremely popular in Japan. The disc was widened to 12 centimeters (about 4 3/4 inches) so that it could hold a maximum of 74 minutes, a limit later slightly extended by improvements in disc mastering. The disc size has proved to be convenient for most CD applications, has imposed itself on the DVD and SACD, and will apparently survive into the high-def DVD format(s).
Polycarbonate is still used as the substrate material. Previously it had been employed as a type of bulletproof “glass” and in airliner windows. It’s tougher than the plastic in laserdiscs and much less sensitive to environmental factors like humidity. All of my discs of 20 years ago still play, even the ones I had boiled as part of an experiment to see if I could destroy them!
• Reed-Solomon digital error correction.
The CD format was the first consumer product to exploit the specialized mathematical area of digital error correction, which had been used in such applications as communications with space probes. In addition to the PCM audio, the system records “redundant” data, mathematically derived from the audio, that are used in playback to identify and correct errors that arise from disc defects and damage. Without error correction, CD playback would be filled with clicks and pops, and it would be very sensitive to scratches and fingerprints. The same type of error correction is still hard at work in the DVD system.
Beyond the fundamental technology, a look at the Sony CDP-101 reviewed in that 1982 article reveals that some of its features were themselves trend-setting. Take its slide-out disc drawer, for instance — now virtually the standard way to get a disc into all kinds of players except car units, portables, boomboxes, and megachangers. The CDP-101 was the only first-generation player to have a disc drawer. The first Philips player had a pop-up lid, while all the others had some variation of a front-panel flip-down door, with the disc held vertically as in a cassette deck. Apparently competitors were surprised by Sony’s move, since all its publicly displayed prototypes had been flip-down devices. The slick, smooth drawer operation, as well as its greater resistance to improper disc loading, were quickly adopted throughout the industry, with flip-down models disappearing in the second generation of players.
Some seemingly trivial things made their debut with the CDP-101 and other players. The “next track” symbol (an arrowhead pointing into a vertical bar) was then brand-new but is now found on DVD players and even computer players and jukebox software. Infrared remote controls, like the one supplied with the CDP-101, got their biggest push with CD players. You need only glance at your coffee table to see how important that development was.
We hardly take notice anymore of the accurate track information (number and time) displayed on a player’s front panel. But this welcome innovation was made possible by the CD format’s provision for recording a table of contents as well as time codes on the disc, information that also enables the rapid and accurate cueing we take for granted with both CDs and DVDs.
Since the introduction of the CDP-101 and other players, we’ve seen the cost, size, and weight of CD players plummet and their portability increase to the point where you can get playback times of more than 12 hours on a single AA battery. Performance has improved, too, though not as much in recent years since the best players — which usually masquerade as DVD players — are now providing audio quality right at the theoretical limits of the 16-bit encoding system. (Thanks to Stanley Lipshitz and John Vanderkooy at the Univeristy of Waterloo in Ontario for helping establish those limits, on which we’ve based our player test procedures.)
Much of the improvement comes from the use of delta-sigma digital-to-analog (D/A) converter chips — often, mistakenly, called 1-bit converters — which enable very low-distortion conversion at low cost. Delta-sigma converters, now used in many industries, got their big initial push from the requirements of digital audio.
In addition to 2003 being the 20th anniversary of the introduction of the CD in the U.S., it’s also been some 20 years since Toshi Doi, then head of Sony’s CD program, took me aside during a break in a lecture/demonstration here in New York City to tell me that Sony was introducing the CD not to show off its technological prowess, or because it needed the hardware business, but “to save the music industry.” It’s a sad irony of history that, this miracle being accomplished, the very music industry that was saved is now trying to make CDs unplayable by loading them with anticopying features that violate the CD standard — that still-stunning landmark of audio innovation.
