Master Quality Authenticated
Master Quality Authenticated (MQA) is an audio codec intended for high fidelity digital audio internet streaming and file download.[1] Launched in 2014 by Meridian Audio, it is now owned by MQA Ltd, which carries out research and development, and licenses the technology to consumer audio playback system manufacturers, record companies and other music content owners, and to music streaming and download providers. It also licenses the technology to professional audio manufacturers for the production of studio equipment required to make, process and monitor MQA recordings.
History
Announcement of MQA was made on 4 December 2014 at a launch held at The Shard in London,[2] although the concepts underpinning the development had previously been the subject of a presentation to the Audio Engineering Society British Section (10 June 2014)[3] and a paper (published 8 October 2014) presented at the Audio Engineering Society 137th Convention in Los Angeles, CA in October 2014.[4]
MQA was demonstrated to visitors to the Consumer Electronics Show in Las Vegas in January 2015.[5] Several download/streaming services, playback system manufacturers and record labels have subsequently announced support for the technology, including Pioneer Corporation, Onkyo, Meridian Audio, 7digital, Norwegian label Lindberg Lyd (2L), Mytek and others,[6] with Warner Music Group announcing the signing of a "long-term licensing deal" with MQA at the Munich High End show in May 2016.[7]
In May 2016, the Recording Industry Association of America (RIAA), in cooperation with the Recording Academy Producers & Engineers Wing, the American Association of Independent Music (A2IM), and DEG: The Digital Entertainment Group, announced that services providing music encoded in MQA are eligible to carry the industry’s official logo mark for 'Hi-Res MUSIC'.[8]
Codec description
The basic premise is to hierarchically compress the relatively little energy in the higher frequency bands into compressed data streams, which are then embedded into the lower frequency bands using proprietary dithering techniques.
After a series of such manipulations, the resulting 44 kHz data, the layered data streams, and a final "touchup" stream (compressed difference between the lossy signal from unpacking all layers and the original) are provided to the playback device. Given the low amount of energy expected in higher frequencies, and using only 1 extra frequency band layer (upper 44 kHz band of 96/24 packed into dither of 48/16) and one touchup stream (compressed difference between original 96/24 and 48/16) are together distributed as a 48/24 stream, of which 48/16 bit-decimated part can be played by normal 48/16 playback equipment.
One more difference to standard formats is the sampling process. The audio stream is sampled and convolved with a triangle function, and interpolated later during playback. The techniques employed, including the sampling of signals with a finite rate of innovation, were developed by a number of researchers over the preceding decade, including Pier Luigi Dragotti and others.[9] The use of these novel sampling technologies may result in standard methods of analysing conventional digital audio content producing meaningless or misleading results when applied to MQA files.
MQA-encoded content can be carried via any lossless file format such as FLAC or ALAC: thus MQA is not a file format itself but an end-to-end encode/decode scheme that is employed in conjunction with available lossless file formats.
One of the features provided by MQA is the ability to play an encoded file or stream without decoding as 48/16 PCM on legacy devices.
Reception
While the technology has received little comment in the general and mainstream press, it has been exalted by the audiophile and hi-fi press. Robert Harley, editor of The Absolute Sound has referred to it as "The most significant audio technology of my lifetime".[10] Editor John Atkinson writing in Stereophile magazine following the UK launch in December 2014 wrote "In almost 40 years of attending audio press events, only rarely have I come away feeling that I was present at the birth of a new world."[11]
Some critical but primarily speculative comments have been made in online forums such as the Computer Audiophile forum[12] and in audio magazine website comments, and a few writers have expressed concern in some areas. Over 80 detailed questions, some of which voiced these concerns, were submitted to the editors of the Computer Audiophile forum and subsequently addressed in detail by the creator of MQA, Bob Stuart, in an extended question-and-answer article.[13]
Decoders
For partners interested in playing back the format, MQA Ltd provides a reference decoder design and object code to run on multiple platforms, which is to be integrated or provided as part of MQA-specific firmware. The current reference platform for testing is XMOS xCORE-200. Commercial MQA-capable playback devices require payment of a royalty to MQA Ltd per unit sold.
References
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Also see mp3PRO for MQA-like lossy codec that separates lower and higher frequencies
