Meridian Audio has been causing quite a lot of ruckus of late with their announcement of MQA (“Mastered Quality Authenticated”), a new format that is supposedly going to revolutionize the way we listen to music. In fact, over the last couple of months a number of notable vendors have been getting on the MQA bandwagon. Yet from watching the fancy marketing videos and perusing Meridian’s website, it’s not even clear what MQA actually is?
Luckily, Stereophile’s resident engineer, John Atkinson, wrote a tremendously insightful article about what the technology is and a how it works. In a nutshell, MQA is not really a new format per se, (say like DSD) as it is a new form of LPCM compression that is both lossy and lossless simultaneously!
When the MQA encoder passes over a high-resolution recording (e.g. 24-bit/192kHz), it encapsulates all of the high resolution samples, in particular, frequency data about 48kHz, by overlaying them on top of itself as a standard resolution stream (16-bit/48kHz). It does this by separating each 24-bit sample into a “more significant portion” and “lower significant portion,” where the “more significant portion” represents the first 16-bits and the “lower significant portion” is the lower 8-bits. These lower 8-bits are essentially reused in the standard 16-bit/48kHz stream to encode spectrum information above the 48kHz boundary. Then depending on whether your DAC is MQA enabled or not, it will either recover just the first 16-bits of each sample, making it look like a normal CD stream, or it will extrapolate the entire 24-bit word and reconstruct the original high-resolution recording. Two for the price one!
Addendum: I believe the MQA encoder is using the lower 8-bits based on the patent link I quoted below and the claim by Meridian that MQA is backwards compatible, but I am not 100% sure. If someone can confirm, please post a comment below.
The net result according to Atkinson is a high-resolution stream that has a data rate “to be about 1.5Mbps per channel for a stereo recording, only slightly more than that required for uncompressed CD audio and about twice that required for transmission of a 16/44.1k FLAC or ALAC file (my guesstimate).” That’s pretty impressive, and makes MQA a more attractive streaming format than say pushing uncompressed PCM or even high-res FLAC.
If any of this above sounds even remotely familiar then you probably remember the whole HDCD initiative that was developed in the late ’90s and then bought by Microsoft in 2000 before they eventually abandoned it in 2005. Very briefly, HDCD encoded 20-bit sized samples in a 16-bit word thereby increasing a CD’s dynamic range. But this time around it seems MQA is more concerned about encoding frequency information than it is about extending bit-depth.
The astute reader will also note that by reducing the bit depth from 24 to 16, the 16-bit only stream is technically a lossy version of the original MQA encoded 24-bit recording. That’s right, for all of Meridian’s song and dance about how folks didn’t ask for low quality audio (i.e lossy), the fact is their MQA encoding scheme technically delivers just that. No worries though, since according to a patent filed by Meridian, that’s just peachy:
“Preferably, the first lossy representation is an accurate representation of the input audio signal other than the effects of time-invariant filtering, sample rate reduction and requantisation that imposes a time-invariant noise floor. If all quantisations, including those within the sample rate reduction, are performed to a constant bit depth and with appropriate dither, the “lossy” representation can be of a standard equivalent to CD quality and would have been considered “audiophile” reproduction only a few years ago. This is in contrast to traditional “lossy codecs” which dynamically adapt the spectral noise floor and sometimes the bandwidth in response to the input signal.”
Note, Meridian’s claim that their lossy scheme sounds better than an equivalently encoded MP3 or AAC is complete conjecture on their part. Until MQA gets peer reviewed, call me skeptical.
Now if MQA was just a clever encoding scheme I would leave it here and petition for a sample for review. Unfortunately, as I recently found out reading the official transcript of Meridian’s CES 2015 FAQ, MQA is actually just one piece to the overall Meridian puzzle:
“As will become clear in our answers, MQA is one of the technologies in Meridian’s Versatile Distribution system. MQA is also our ‘umbrella’ term for the suite of technologies and underlying audio coding philosophy, which itself goes beyond recording. Master Quality Authenticated captures the ethos of the enterprise and the MQA stream is central to distribution.
Related Pages:
The MQA technologies include: Archive extraction and creation, forensic and recording tools; advanced A/D and D/A conversion; Encapsulation to a kernel; MQA lossless coding; MQL (triply-compatible lossless bandwidth-extension) lossless compression; Playback Rendering. A glossary will follow.”
If you haven’t guessed where I’m going with this, I’ll give you a hint: It starts with ‘D’ and ends with ‘M.’
- The MQA syntax supports a hierarchy of authentication keys using strong encryption. The encryption protects the encoding/decoding instructions, various metadata and verification of both lossless digital transmission from studio to decoder and ‘beyond digital lossless’, it authenticates the analogue-to-analogue path — which is a major step forward in sound quality.
This sounds very similar to the way web-based public key certificates are issued by a certificate authority, Reading into the above a little, it seems that these keys will be used to validate a file’s pedigree and allow or block access to those precious lower 8-bits in the MQA encoded file.
- At the lowest level the keys verify that the stream is genuinely MQA. This is important for the full benefit of Authentication to be realised and we hope that facility will ignite new and enriched ways for artists to communicate with fans and for listeners to appreciate ‘the real thing’. MQA is neither a DRM nor conditional-access system; listeners can still enjoy the music without a decoder in a variety of legacy playback scenarios, in actual CD quality. However the keys protect the ecosystem.
Alright, perhaps it’s not DRM in the classical sense since it doesn’t actually prevent copying or playback, but it certainly seems that Meridian is shooting for having some kind of “degraded” playback mode whereby without MQA enabled software you won’t be able to play the full high-resolution stream, i.e. you’re stuck with the 16-bit “lossy” version which technically speaking is less than what you would have had with a CD. (Dual layer SACDs work the same way. You can copy and listen to the CD layer on any device, but the protected SACD layer requires a dedicated SACD player and can’t be copied. -Dave)
- The hierarchy of keys, in principle allow us to have streams which are verifiable for different things, ranging from, e.g. genuine MQA in a local ecosystem, to a fully-authenticated path from artist/studio to the listener. This highest level we call ‘MQA Studio’. In principle these levels can be displayed on a UI and licensed decoders are required to indicate this. In the middle are levels of authentication that can be applied by a distribution house, mastering studio, broadcast, etc.
The idea of requiring “licensed decoders” for playback just gives me the willies. Imagine every open source player software had to pay Meridian a license fee in order to play MQA files fully. In fact, in the Atkinson article I referenced above, he even mentions that Meridian was nebulous regarding MQA’s licensing terms.
- How intermediate keys will be used is not fully settled and we are in consultation with music industry partners.
- We fully expect to have a variety of options available for smaller-scale encoding requirements but can’t comment just yet. Suffice it to say that the MQA initiative is supported by music companies and it is our intention to make access very inclusive and convenient.”
Sure it is.
I’m going to go out on a limb here but I think this is another scheme to ram DRM down the consumer’s throats, or at least has the potential to do so. As I said above, it’s not DRM in the classical sense since the MQA ecosystem doesn’t prevent unauthorized distribution or “lossy” playback. Nevertheless, it does offer content providers this degraded playback mode which maybe a tool to prevent pirating and/or legal backup. Of course hopefully I’m completely wrong and reading way too much into Meridian’s announcements. Time will tell.
Finally, it is still not even clear to me what MQA offers over plain old high-resolution FLAC other than a reduced data rate, which I admit is attractive for streaming providers like Tidal. But in the end, with folks streaming mainly over iDevices and their Android equivalents, why would anyone want to waste their data plan on higher resolution audio? Beats me.
Regardless, I am still curious about MQA and hope to get a chance to critically listen to a recording that uses it – but not Enter Sandman. Ouch.