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Questions of Impedance Interaction
Thomas J. Norton  |  Jan 06, 1994  | 
On a number of occasions we have commented on the effects of an amplifier's output impedance on a system's performance. A high output impedance—such as is found in many tube amplifiers—will interact with the loudspeaker's impedance in a way which directly affects the combination's frequency response. The Cary CAD-805, for example, has a lower output impedance than most tube amplifiers, and should be less prone to such interaction. Some months back—before the CAD-805 arrived—I investigated this phenomenon in conjunction with measurements for a forthcoming review of the Melos 400 monoblock amplifier. Since the Melos 400 also had a relatively low output impedance for a tube amplifier (at 0.43 ohms at low and mid frequencies, rising to 1.2 ohms at 20kHz, from its 8 ohm tap), I took that opportunity to run some frequency-response measurements using an actual loudspeaker as the load for the amplifier.
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ReferenceFeatures
A Transport of Delight: CD Transport Jitter
Robert Harley  |  Nov 01, 1993  | 
Not that long ago, digital audio was considered perfect if all the bits could be stored and retrieved without data errors. If the data coming off the disc were the same as what went on the disc, how could there be a sound-quality difference with the same digital/analog converter? This "bits is bits" mentality scoffs at sonic differences between CD transports, digital interfaces, and CD tweaks. Because none of these products or devices affects the pattern of ones and zeros recovered from the disc, any differences must be purely in the listener's imagination. After all, they argued, a copy of a computer program runs just as well as the original.
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Reference
Jitter & the Digital Interface
Rémy Fourré  |  Aug 08, 2004  |  First Published: Oct 01, 1993  | 
Until recently, all problems in digital audio systems were blamed on either the analog/digital converters (ADCs) used in mastering or the digital/analog converters (DACs) needed for playback (footnote 1). As the performance of both ADCs and DACs improved, however, a previously unrecognized mechanism for distortion was unmasked: jitter. As we shall see, jitter—or, more correctly, word-clock jitter—can be a significant limitation in the technical and sonic performance of digital audio systems (footnote 2).
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ReferenceJ. Gordon Holt
Sounds Like? An Audio Glossary
J. Gordon Holt  |  Jul 29, 1993  | 
Subjective audio is the evaluation of reproduced sound quality by ear. It is based on the novel idea that, since audio equipment is made to be listened to, what it sounds like is more important than how it measures. This was a natural outgrowth of the 1950s high-fidelity "revolution," which spawned the notion that a component, and an audio system as a whole, should reproduce what is fed into it, without adding anything to it or subtracting anything from it.
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ReferenceAs We See It
The Stereo Soundstage
Peter W. Mitchell  |  Jul 29, 1997  |  First Published: Jul 29, 1993  | 
What is the angular separation of your loudspeakers as viewed from your favorite chair? Whatever your answer, it's wrong. Of course I don't mean that it's a factually incorrect answer, just that any single value of subtended angle cannot be ideal for all recordings.
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Reference
What It All Means: line-level preamplifier measurements
Thomas J. Norton  |  Jan 29, 1993  | 
Though we sometimes take for granted that the basic "language" of our measurements is clear to all of our readers, letters to the editor tell us that this is not the case. Periodically, then, we will attempt to explain exactly what our measurements are and what they purport to show. Though those with technical training may find our explanations a bit simplistic, they're aimed at the reader who lacks such experience.
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Reference
Holiday Reading
John Atkinson  |  Jan 17, 1993  | 
I recently scoured my shelves and came up with the following list of must-read books for stereophiles, all of which are in print and should be available from specialist bookshops or from the suppliers mentioned in the text. Books marked with an asterisk (*), though too technical for the general reader, will be found rewarding by those who have a good grasp of mathematics and who want to delve deep. Reading the books in the first "general" section of the list will enable readers to understand just about everything that appears in Stereophile, but all the books listed contain between their covers untold treasures.
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Reference
Pace, Rhythm, & Dynamics
Martin Colloms  |  Nov 24, 1992  | 
Martin Colloms (footnote 1) suggests that the traditional ways of assessing hi-fi component problems overlook the obvious: does the component dilute the recording's musical meaning?
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ReferenceFeatures
A Question of Bits
Peter W. Mitchell  |  Aug 29, 2004  |  First Published: Sep 01, 1992  | 
Someday we may speak wistfully to our grandchildren about the "golden age" of digital audio when consumer formats (CD and DAT) contained a bitstream that was an exact bit-for-bit duplicate of the original studio master recording—not a digitally compressed, filtered, copy-resistant version whose sound is "close enough" to the original. Digitally compressed formats such as DCC and MiniDisc represent, in effect, a return to the pre-CD era when consumer-release formats were always understood to be imperfect copies of the studio original. Even the most ardent audiophile accepted the fact that LPs and mass-produced tapes did not, and could not, sound as good as the master tapes they were derived from.
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FeaturesReference
The Sound of Surprise (the loudspeaker/stand interface)
John Atkinson  |  Jun 30, 1995  |  First Published: Jun 30, 1992  | 
One of the great imponderables in hi-fi is how much the vibrations of a dynamic loudspeaker's cabinet walls contribute to its overall sound quality. Studies by William Stevens in the mid-1970s showed that, with some speakers, the acoustic output of the enclosure could be almost as much as that from the drive-units. Since then, responsible speaker designers have worked hard either to damp cabinet vibrations or to shift them to higher frequencies where their effect on the music will be less deleterious.
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Reference
Noise, Modulation, & Digital/Analog Conversion
Robert Harley  |  May 30, 2004  |  First Published: Feb 01, 1992  | 
At the February 1991 Audio Engineering Society Convention in Paris, Audio Precision's Dr. Richard Cabot (see my interview in January 1991, Vol.14 No.1) proposed a new technique for measuring noise modulation in D/A converters (footnote 1). The method, based on psychoacoustic principles, attempts to predict the audible performance of D/A converters. Now that Stereophile has added digital-domain signal generation and analysis to our Audio Precision System One, we can employ Dr. Cabot's technique and see if there are any correlations with subjective performance.
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ReferenceFeatures
The Listeners' Manifesto
Robert Harley  |  Jan 01, 1992  | 
Editor's Note: This article is now only available as an Audio Engineering Society preprint, under the title "The Role of Critical Listening in Evaluating Audio Equipment Quality," preprint number 3176. The price is $4.00 for AES members, and $5.00 for non-members; it can be ordered (currently on paper only, not as a downloadable pdf) by entering the number in the appropriate field on the preprint search page at the AES website.
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Reference
The Jitter Game
Robert Harley  |  Jul 04, 2004  |  First Published: Jan 01, 1992  | 
"How sour sweet music is
When time is broke and no proportion kept!"
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FeaturesReference
Harmonic Convergence: the Effect of Component Tweaking
Ben Duncan  |  Oct 10, 2019  |  First Published: Jan 01, 1992  | 
Power amplifiers fascinate me. In the past 15 years I've helped design and build over a dozen advanced models, with output powers ranging from 50 to 2500W, for a number of the UK's professional equipment manufacturers. To learn from others' ideas and mistakes, I've also repaired, measured, used, and reviewed hundreds of makes of amplifier. My experiences have led me to regard the power amplifier as one of the messiest, most imperfect pieces of electronic equipment in the record/replay path.
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Reference
Basso Profundo
Martin Colloms  |  Dec 29, 1991  | 
Bass constitutes one of the least understood aspects of sound reproduction. Opinions vary greatly on matters of bass quality, quantity, and perceived frequency range or response. Moreover, the bass region is subject to the most unwanted variation in practical situations due to the great influence listening-room acoustics have on loudspeaker performance. Every room has its different bass characteristic, and changes in the position of speakers or listener also constitute major variables at low frequencies.
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