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The Analog Compact Disc

Nothing quite new is perfect. —Marcus Tullius Cicero, Brutus

Back in the days when vinyl was our only source of high-quality recorded music, the first question when playing a new record was often, "How good is the pressing?" LPs varied so much in their mastering and pressing qualities that buying a new one was often a crapshoot.

With the advent of the digital compact disc, however, few of us bother to think about variations in CD quality. We assume that if the CD spins and makes sound, the disc must have been manufactured perfectly.

In reality, compact discs vary greatly…

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Because the pits and land have nine discrete lengths, the signal reflected from the disc to the photodetector is composed of nine discrete frequencies. The shortest pit or land length produces a frequency of 720kHz; the longest pit or land length produces a frequency of 196kHz. These nine discrete frequencies are easily seen in the signal output from the photodetector. This signal, called the "HF" (High Frequency) signal, is ultimately decoded and converted into raw digital-audio data, then into an analog audio signal. Although the HF signal is a series of sinewaves, the digital data are…

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All three discs sounded different, the Zeonex sounding the best. The standard disc had a drier, more forward sound, with less depth. The treble was more forward, yet the sound lacked the air, openness, and extension heard on the Zeonex disc. The Zeonex disc's bass was also better defined, and I heard an overall increase in resolution, with more musical information presented.

These sonic differences may be regarded as slight or even imperceptible to the casual listener through a low-quality stereo system. But to the audiophile with a keen ear, an open mind, and a high-resolution playback…

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That's right; the amount of jitter on a compact disc is influenced by the highly variable mastering and developing processes—and the quality of the mastering machine itself.

Jitter has recently become a hot topic in the CD-manufacturing business. When the CD specification was created (codified in the Philips "Red Book" standard), jitter was never even mentioned, much less specified. Now manufacturers of CD-mastering machines are touting their models as having "low jitter," and disc replicators are beginning to measure jitter in the HF signal as part of the quality-assurance process.…

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In addition, mishandling increases a disc's data errors. A CD's top (label) side is more vulnerable than the bottom, because the pits are impressed on the label side. Scratches or contamination on the bottom surface are out of focus to the laser, and are less likely to cause errors. But scratches on the top surface can wipe out large areas of pits. The photograph in fig.7 is a CD surface on which I made a mild abrasion with a ball-point pen—mild by unmagnified visual standards. On the CD's pit scale, however, this "mild" scratch produced catastrophic damage to the spiral track.

…

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A parameter called a "dropout" is defined as an instance in which the signal coming off the disc drops below 30% of its nominal value. Large errors combined with a dropout indicate physical damage to the disc. Large errors without a dropout could be caused by localized areas of poor pit geometry.

Although these errors are completely corrected, a disc with high error rates will have less tolerance for scratches, dirt, fingerprints, and poor-quality CD players before producing an uncorrectable error. This is especially important in CD-ROM, where bit-for-bit accuracy is essential.

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The Analog Compact Disc Clover Systems QA-101 CD Analyzer

Sidebar: Clover Systems QA-101 CD Analyzer

Looking at error rates on CDs was once the domain of specialized test instruments costing tens of thousands of dollars. These CD analyzers were highly sophisticated, and often provided all kinds of statistical and graphic plotting functions useful when characterizing the quality of large quantities of CDs. The high cost and complexity of CD analyzers excluded all but CD replicators from knowing how well—or how poorly—CDs were made.

All that has changed with a new CD analyzer made by Clover Systems of Laguna Beach, California. The Clover…

Recording of August 2000: Mahler: Symphony 6

MAHLER: Symphony 6
Manhattan School of Music Symphony Orchestra, Glen Cortese (cond.)
Titanic 257 (CD). 2000. Charles G. Thomas, exec. prod., Jerry Bruck, eng., Michael Karas and Eric Wagner, assoc. engs. AAD? TT: 76:27
Performance: ****?
Sonics: *****

With such glamorous competition on the Mahler market, what could a student orchestra from the Manhattan School of Music and a virtually, unknown conductor have to offer the international recording world? Plenty, as it turns out. Critics begged for a Mahler moratorium in the early 1990s when everybody but Christopher Hogwood…

The Blind Leading the Blind?

The first epiphany I experienced in blind audio testing took place in the Dunfey San Mateo Hotel, in Northern California. We were stuffed into a largish, well-lit room in which dozens of listeners sat in chairs, and others stood around the back or sat on the floor. Up front were two large B&W Matrix 801 speakers on tall stands spaced far apart, behind them, opaque curtains hid a small pile of audio equipment. John Atkinson and Will Hammond stood at stage left.

The occasion was the 1989 High End Hi-Fi Show (many audiophiles still call it the "Stereophile Show," even though it has…

The Blind Leading the Blind? Letters, October 2005

Letters in response appeared in October 2005 (Vol.28 No.10):

Curious

Editor: There was a curious juxtaposition of editorial content and advertising in the August 2005 Stereophile. Page 3 has Jon Iverson discussing the problems of double-blind testing, and concluding that such testing can identify only who has the best ears. Yet then, on p.7, Revel, a respected high-end speaker manufacturer, talks about how their new and most affordable line of speakers were "subjected to the ultimate test—double-blind listening." Are we to believe Mr. Iverson or Revel? Does the editorial half of…