MQA

MQA involves two fundamental concepts, discussed in a paper presented to the Audio Engineering Society in October 2014, the first responsible for a potential improvement in sound quality, the second responsible for a large reduction in the bandwidth required for storage and streaming of high-resolution files...

As I wrote in the January issue's "As We See It," Master Quality Authenticated (MQA), the encoding/decoding system developed by J. Robert (Bob) Stuart and Peter Craven, has been widely criticized, despite reports in this magazine and others that MQA-encoded files tend to sound better than the PCM originals from which they were derived. Also in last month's issue, Jim Austin investigated the time-domain performance of the MQA reconstruction filter and I examined some of the more general aspects, ending with: "Other criticisms of MQA involve its implications for the recording industry, for manufacturers of audio products, and for consumers. I will examine those in next month's 'As We See It.'"

Despite there now having been many opportunities for audiophiles to compare MQA-encoded recordings with the PCM originals—as well as comparisons at shows and dealer events, the Norwegian 2L record label has offered downloads of MQA/PCM files for quite a long time—there are still members of the press who insist that no-one, other than some reviewers, has been able to perform such comparisons. At the 2017 LAAS, not only were some exhibitors demonstrating MQA—Aurender, Meridian—Covina, CA retailer Sunny Components devoted the show's Saturday afternoon to specific comparisons hosted by MQA's Bob Stuart and Wilson Audio's Peter McGrath.

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.

CES 2016 marked the first time that three writers for Stereophile—Editor-in-Chief, John Atkinson; AnalogPlanet analog guru, Michael Fremer; and this Contributing Editor—could sit down in the same room with Bob Stuart of MQA/Meridian and spend a concentrated amount of time comparing before- and after-MQA encoded (Master Quality Authenticated) tracks.

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.