Master Quality Authenticated (MQA): The View From 30,000 Feet

Blog
Categories:
Disc players,
Digital-to-analog converters
Master Quality Authenticated (MQA): The View From 30,000 Feet

The other problem with “high-resolution” digital audio is that it didn’t really solve the fundamental problem of why digital sounds the way it does—flat, congested, hard, and glassy. Digital audio requires low-pass “brickwall” filters to prevent a type of distortion called “aliasing.” But these filters introduce ringing, or a smearing of musical signals over time. Despite attempts to minimize this distortion through faster and faster sample rates (the filters for which are less sonically detrimental), digital audio was constrained by the very fundamentals of sampling theorem codified more than fifty years ago.

So-called “high-resolution” downloads also exact a price in massive file sizes. Increasing the sampling rate reduces, but doesn’t eliminate, the flaws built into the very foundations of digital audio as it has been implemented. Moreover, very fast sampling is preposterously wasteful; most of those additional bits carry no real information whatsoever. Consider that a 192kHz/24-bit system allocates the bits to encode a 90kHz sinewave at full-scale amplitude, a signal that wouldn’t even come close to existing in the real world. High sample rates create a massive container for the music (a 96/24 or 192/24 file) that is largely wasted bits. It’s like shipping a paperback book in a box the size of a filing cabinet. Moreover, obtaining these files, and playing them back correctly, requires specialized computer expertise, making them accessible only to the committed.

To summarize, the audible degradation in digital audio is largely caused by filters. The industry then tries to minimize that degradation by very fast sampling and the gentler filters possible with faster sampling, which creates massive files and limits their accessibility to the vast majority of listeners. The record industry is reluctant to release their fast-sampling files for fear that they will eventually have nothing to sell. Consumers who want better-than-CD quality must master computer technology, limiting the widespread accessibility of better sound. Even then, the library of available music is limited, and still doesn’t represent the sound in the recording studio. To top it off, the consumer never really knows if the file he’s playing back is the same as that created by the artist and engineer. And those enormous files can’t be streamed, and won’t play in portable applications.

In short, the technology is broken. The business model is broken. The artist is unable to deliver to fans the best possible representation of his or her work. The consumer is denied the best possible listening experience.

We ended up in this predicament because each improvement in digital audio was merely an incremental evolution of conventional ideas and models. No one had gone back to first principles and rethought how best to record and distribute music.

Against this backdrop, Master Quality Authenticated emerged. In a single stroke, MQA solves all these problems, from the technical, to the business model, to the sound quality, to the easy accessibility of that sound quality, and to the communication between artist and listener.

How does it do this? For starters, it turns out that the “laws” of Nyquist-Shannon sampling theorem—which have dictated the design of brickwall filters since digital audio’s inception—are not quite ironclad. Since Shannon, sampling theory has advanced considerably, driven by research in other fields such as medical imaging and astronomy that face challenges parallel to those of audio. Also, sounds that are important to humans have very specific statistics including a 1/f tendency (the power spectral density is inversely proportional to frequency; i.e. the higher frequencies have less energy), in part resulting from how sound behaves in air, a factor not considered by the classic sampling criteria.

Consequently, Nyquist-Shannon isn’t the limiting factor it once was, but it took some minds from the audio world (MQA inventors Bob Stuart and Peter Craven) to recognize that fact and apply these advanced new techniques to music reproduction. MQA incorporates this latest sophisticated thinking into a different sampling design, reducing the filters’ “temporal blur” and with it the degradation that has plagued digital audio since its inception.

In addition to delivering unprecedented sound quality, MQA offers record companies a compelling solution to delivering to consumers the best possible sound while still protecting their archives. When you play an MQA file through an MQA decoder, you hear the high-resolution studio master, yet you never actually possess the high-resolution studio master. That high-resolution signal exists only at the decoder output, in analog form but matches very closely the analog in the studio. Of course, you can store an MQA-encoded file (it’s formatted as a 44.1 or 48kHz/24-bit FLAC file) with all the high-resolution information embedded in it, but to access that hi-res information you must play it back. It must be noted here that MQA has no form of copy protection or digital-rights management (DRM) whatsoever. Contrary to what some Internet posters think, MQA is not an evil scheme to institute DRM.

A much more efficient coding technique captures all the musical information while not trying to encode signals that don’t exist in the real world. This approach results in much smaller file sizes with no loss in sound quality. In addition, a clever technique encapsulates the high-resolution portion of the signal and hides it under the noise floor. This information “unfolds” on playback, with awareness of the playback platform, into the signal’s original resolution, all the way up to 352kHz/24-bit.

Another benefit to record companies and consumers is that one MQA file serves all listeners, and will play anywhere. Record companies must now create and offer MP3, AAC, Red Book, 96/24, and many other versions of the same music. The same MQA file will go to everyone.

Finally, MQA provides a direct link between artist and listener in the form of the authentication feature—the light on the decoder that confirms that the file being decoded is the file created in the studio. The mastering engineer can monitor the signal through the entire encode-decode chain, and hear exactly what the listener will hear. Conversely, the listener hears exactly what the engineer created.

The surprising advances and innovative thinking that MQA has introduced will forever change the way we and future generations consider digital audio, even if MQA never becomes a large-scale commercial reality. But I’m betting that it will.

http://www.theabsolutesound.com/articles/beyond-high-resolution/

http://www.theabsolutesound.com/articles/meridians-master-quality-authenticated-the-interview/

http://www.theabsolutesound.com/articles/from-the-editor-mqa-on-the-threshold/

Featured Articles

Lists