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John Atkinson  |  Nov 07, 1998  |  2 comments
This series of articles was initially written (in slightly different form), as a paper presented at the 103rd Audio Engineering Society Convention, New York, September 1997. The preprint, "Loudspeakers: What Measurements Can Tell Us—And What They Can't Tell Us!," AES Preprint 4608, is available from the AES, 60 East 42nd Street, Room 2520, New York, NY 10165-0075. The AES internet site, offers a secure transaction page for credit-card orders.
John Atkinson  |  Jan 28, 1999  |  0 comments
This series of articles is based on a paper presented at the 103rd Audio Engineering Society Convention, New York, September 1997. The preprint, "Loudspeakers: What Measurements Can Tell Us—And What They Can't Tell Us!," AES Preprint 4608, is available from the AES, 60 East 42nd Street, Room 2520, New York, NY 10165-0075. The AES internet site, www.aes.org, offers a secure transaction page for credit-card orders.
John Atkinson  |  Dec 14, 1998  |  0 comments
This series of articles was initially written (in slightly different form), as a paper presented at the 103rd Audio Engineering Society Convention, New York, September 1997. The preprint, "Loudspeakers: What Measurements Can Tell Us—And What They Can't Tell Us!," AES Preprint 4608, is available from the AES, 60 East 42nd Street, Room 2520, New York, NY 10165-0075. The AES internet site, www.aes.org , offers a secure transaction page for credit-card orders.
John Atkinson  |  Mar 08, 2008  |  14 comments
As Wes Phillips recently reported on this website, CD sales are down and legal downloads of audio files are up. Stereophile has been criticized more than once for not paying enough attention to the subjects of MP3 and other compressed file formats, such as AAC, and for offering no guidance at all to readers about how to get the best sound quality from compressed downloads.
Jim Austin  |  Feb 13, 2018  |  177 comments
When you come to a fork in the road, take it.—Yogi Berra

Over one busy week in 1986, Karlheinz Brandenburg laid the foundation of a technology that a few years later would upend the record business. Brandenburg, a PhD student in electrical engineering at the Friedrich-Alexander University Erlangen-Nuremberg, was figuring out how to code digital music efficiently enough that it could be delivered over digital telephone lines. A patent examiner had concluded that what the application proposed was impossible, so over a week of late nights, Brandenburg produced the proof of concept and more. It was another decade before the technology—MPEG-2 level III, more commonly known as MP3—would find its true home, the Internet.

Jim Austin  |  Jan 06, 2018  |  28 comments
Loss is nothing else but change, and change is Nature's delight.—Marcus Aurelius

Master Quality Authenticated (MQA), the audio codec from industry veterans Bob Stuart and Peter Craven, rests on two pillars: improved time-domain behavior, which is said to improve sound quality and what MQA Ltd. calls "audio origami," which yields reduced file size (for downloads) and data rate (for streaming). Last month I took a first peek at those time-domain issues, examining the impulse response of MQA's "upsampling renderer," the output side of this analog-to-analog system (footnote 1). This month I take a first look at the second pillar: MQA's approach to data-rate reduction. In particular, I'll consider critics' claims that MQA is a "lossy" codec.

Jim Austin  |  Dec 12, 2017  |  213 comments
I don't think I've ever seen an audio debate as nasty as the one over Master Quality Authenticated (MQA), the audio-encoding/decoding technology from industry veterans Bob Stuart, formerly of Meridian and now CEO of MQA Ltd., and Peter Craven. Stuart is the company's public face, and that face has been the target of many a mud pie thrown since the technology went public two years ago. Some of MQA's critics are courteous—a few are even well-informed—but the nastiness on-line is unprecedented, in my experience.
Jim Austin  |  Apr 19, 2018  |  47 comments
In an article published in the March 2018 Stereophile, I wrote that critics have been attacking MQA, the audio codec developed by J. Robert Stuart and Peter Craven, by accusing it of being lossy. The critics are right: MQA is, in fact, a lossy codec—that is, not all of the data in the original recording are recovered when played back via MQA—though in a clever and innocuous way. For MQA's critics, though, that's not the point: They use lossy mainly for its negative emotional associations: When audiophiles hear lossy, they think MP3.
Jim Austin  |  May 17, 2018  |  160 comments
The right thing at the wrong time is the wrong thing.—Joshua Harris

The sampling theory formulated by Claude Shannon in the late 1940s had a key requirement: The signal to be sampled must be band-limited—that is, it must have an absolute upper-frequency limit. With that single constraint, Shannon's work yields a remarkable result: If you sample at twice that rate—two samples per period for the highest frequency the signal contains—you can reproduce that signal perfectly. Perfectly. That result set the foundation for digital audio, right up to the present. Cue the music.

J. Robert Stuart  |  Aug 11, 2016  |  117 comments
Author's Note: We are grateful to Stereophile for the opportunity to address some frequently repeated technical questions appearing in comments to articles. Recently this has included misunderstandings about noise calculation, dynamic range, resolution, definition, music spectra, channel capacity, lossless processing and temporal aspects of digital channels.

To simplify this document we have grouped the topics and set them as questions and answers either as response, tutorial or axiom. Some months ago we published a comprehensive Q&A for an online forum and to avoid repetition we occasionally refer to topics already discussed there (see [37] in the "References" sidebar).—J. Robert Stuart

John Atkinson  |  Oct 24, 2008  |  0 comments
"Physical discs seem so 20th century!" That's how I ended my eNewsletter review of the Logitech (then Slim Devices) Squeezebox WiFi music server in April 2006, and it seems that increasing numbers of Stereophile readers agree with me. In our website poll of January 5, 2008, we asked, "Are you ready for an audiophile music server?" The response to that question was the highest we have experienced: 32% of respondents already listen to music via their computer networks, many using home-brewed solutions, and 44% intend to. We've published a lot of material on this subject in the last five years, and it seemed a good idea to sum it up in this article.
Keith Howard  |  May 02, 2004  |  First Published: Apr 01, 2004  |  0 comments
Looked at from one viewpoint, DVD-Audio and SACD appear to be exercises in sheer profligacy. In the case of DVD-A, why provide a maximum bandwidth almost five times what is conventionally taken to be the audible frequency range, and couple it to a dynamic-range capability far in excess of that achievable by the microphones used to record the sound? In the case of SACD, why provide a potential bandwidth in excess of 1.4MHz, only to fill more than 95% of it with quantization noise?
Jim Austin  |  Oct 02, 2018  |  43 comments
The most notable aspect of Benchmark Media Systems' DAC3 HGC ($2195), which I favorably reviewed in the November 2017 Stereophile (footnote 1), is its low noise floor. John Atkinson's measurements corroborated Benchmark's claim that the DAC3 is capable of "at least" 21-bit performance. While significantly less than the theoretical potential of a 24-bit data format, 21 bits is still the state of the art, and corresponds to a dynamic range—the ratio of the highest achievable digital-domain volume to the DAC's internal noise—of 128dB. That's well above the dynamic range that most power amplifiers can achieve. A good-measuring high-end solid-state amplifier is likely to have a dynamic range—the highest attainable ratio of signal to noise—of about 100dB ref. its maximum power.
Tyll Hertsens  |  Jan 31, 2017  |  10 comments
Some 100 engineers and scientists from around the globe assembled for the Audio Engineering Society's 2016 International Conference on Headphone Technology, in Aalborg, Denmark.

I figured it was coming, but it wasn't until just after I'd returned from the Audio Engineering Society's 2016 International Conference on Headphone Technology—held last August in Aalborg, Denmark—and was writing up my report and summary on the event for InnerFidelity.com (footnote 1) that I knew for sure: Headphones are about to change . . . a lot.

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