Features

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.

In a series of recent feature articles for Stereophile, Jim Austin has examined how the controversial MQA codec works: "MQA Tested, Part 1," "MQA Tested Part 2: Into the Fold," "MQA Contextualized," "MQA, DRM, and Other Four-Letter Words," and, most recently, "MQA: Aliasing, B-Splines, Centers of Gravity." I doubt there is a Stereophile reader who is unaware of the fracas associated with MQA, and I have been repeatedly criticized on web forums for describing its underlying concept as "elegant."

But elegant it is, I feel.

High Definition Compatible Digital^® (HDCD^®), the proprietary process for improving the sound of 16-bit digital audio, has finally arrived. More than a dozen digital processors using the technology are on the market, and the professional encoder used to master HDCD discs is following closely behind.

Do-It-Yourself (DIY) loudspeaker projects are quite common in the UK, where details about several excellent designs, including a recent one by Martin Colloms, have been published for public domain consumption. Stateside, the situation is rather grim, where only an occasional subwoofer project (always popular) makes it into the commercial magazines.

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.

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.

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.