COMPARISON: MQA "Authentication" & Sound Quality? (Mytek Brooklyn & Meridian Explorer2)

You've probably heard or read the catch phrases from MQA over the years. "Revolutionary", "TAKE ME THERE"... "To the original performance..." Or how about using phrases like "end-to-end technology"?

As I have said over the last few months, I don't like talking about MQA based on my general impression of what they're trying to do and the way they try to convey supposed "value" to the audiophile world through their advertisements and sponsored articles in the audiophile press. Nonetheless, sometimes it's just necessary to comment and more importantly to put some of the rhetoric to the test. There appears to be a remarkable schism between those who advocate and praise MQA and those who have concerns. I'm pretty sure there are many wishing that MQA would just go away instead of complicating music playback with yet another questionable variant.

Last week, when I wrote about the idea of MQA CD, I brought up the Pono experience as another example of failure in the recent history of the industry. For Pono, the failure was perhaps rather obvious for those of us who have been listening to 24-bit and >44.1kHz music for awhile, especially those of us who have ever bothered to try an A/B-test. It does not take a genius to realise that audible differences are really quite subtle (if even there in most cases of mainstream music) and that differences do not translate to "benefit". Without clear audible benefits, there really was no way that the promise of the Pono music store could ever excite the music-buying public... Certainly not in the way Neil Young portrayed it (sure, the hardware PonoPlayer is unique but with its own quirks of course).

Part I: Intro / Rationale

When it comes to MQA, it's certainly a bit more complicated. For one, it brings into this world a new encoding system so it's not as easy to compare unless one had a decoder that could easily be switched on/off on-the-fly. But for me at least, right from the start, there were many ideas being floated that just seemed "fishy". How is it possible to honestly say this:

When you're packaging supposedly PCM 24/88+ worth of data into a 24/48 file that maintains compatibility with standard DACs? Obviously some form of lossy mechanism must be involved - is that not a form of sacrifice? And obviously in order to add the encoded data within the package to maintain standard playback compatibility, some potential lower level details will need to be discarded. I agree, it's not unreasonable in a 24-bit file because the lower bits are typically just noise, but still, a potential "sacrifice" of sorts depending on how many bits were affected - the higher the resolution of the original production, the more potential loss of low-level detail. In previous posts, I discussed digitally in software and using the Mytek Brooklyn DAC the effects of MQA decoding.

But there was one idea that always bothered me about the MQA claim worth thinking about... What does it mean above when MQA insists "And because it's fully authenticated, you can be sure you're hearing exactly what the artist approved in the studio"?

What exactly does it mean when they use the word authenticated? And how is this authentication related to the sound "in the studio"?

Notice that MQA is rather careful in the words they use on their website especially related to that second question linking sound quality. However, if you look at the older archives, we see Bob Stuart making a few assertions worth considering and the connotations they create. Here's one from a CEPro article in December 2014 when the press was first introduced to MQA at a company party:

Stuart says that with the development of MQA, listeners can experience their digital audio content at the same quality levels as the professional recording industry. 

“Music lovers need no longer be shortchanged; finally we can all hear exactly what the musicians recorded,” he explains.“MQA gives a clear, accurate and authentic path from the recording studio all the way to any listening environment—at home, in the car or on the go. And we didn’t sacrifice convenience.”

By around CES in January 2015, there was a Q&A posted on Meridian Unplugged and one of the answers went like this from Mr. Stuart:

1. 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.

And later in May 2016, we see this on AudioStream, in the "MQA Reviewed" article:

The MQA authentication ‘light’ indicates Provenance in the source for the file. The MQA display indicates that the unit is decoding and playing an MQA stream or file and denotes provenance that the sound is identical to that of the source material. MQA Studio indicates it is playing a file which has either been approved in the studio by the artist/producer or has been verified by the copyright owner.

And more recently here's a January 2017 video about MQA with various engineers that seem to be hyping this whole "assurance" and "authenticated" bit. For example, what does Morten Lindberg mean by "we have an assurance of how it's going to play back on the other end - that's something we haven't had before":



I added the bold highlights. These are just three examples of the wording being used by MQA/Bob Stuart to suggest that somehow the MQA process retains the "sound" of the studio production. As if there is something special in these MQA files beyond what a standard HDtracks high-resolution download would be able to convey for example. Notice again the careful wording used.

The word authentication basically means "the process or action of proving or showing something to be true, genuine, or valid" - nothing more. In this regard, the little "light" on an MQA DAC would do the job and may be all that Stuart's talking about (whoopee do!). It's not hard to imagine how this is done of course - embed some MQA data in the stream and the firmware detects it. Perhaps something like a CRC may be embedded every so often to make sure the data isn't corrupt and the indicator light will go off or blink perhaps with each instance of corruption.

The words Stuart chooses coyly hints at another meaning; the idea that MQA authentication can perhaps bring the studio sound home when you play an MQA-encoded track. Perhaps hinting that somehow the technology is capable of making DACs sound closer to some kind of studio sonic standard. How are we supposed to interpret "which is a major step forward in sound quality"? Is there any evidence to this? When they speak of "end-to-end technology" ("analogue-to-analogue path"), is there some actual retained "authentic" sound that's different than say an equivalent HDtrack file's playback using that DAC?

One way to test this hypothesis is to check what happens to the sound coming out of two MQA-certified DAC devices. Is there any evidence that MQA processing with its claimed benefits (time domain accuracy, "better" filtering algorithm catering to the DAC, "accurate and authentic path", etc.) will result in sonic output more similar than just the DACs playing the same HDtracks tune? The idea being that if MQA processing makes the DACs sound more alike, then there's actually something being done to standardize the analogue output which ostensibly is a reflection of the "studio sound" or even the sound of the "original performance" when they say stuff like this on their website:

Part II: The Test

With the above in mind, my friend with the professional quality RME Fireface ADC graciously and meticulously recorded the output of two MQA DACs for me as he did with the previous test of hardware decoding from the Mytek Brooklyn (see that post for other details like procedure and settings used). This time, the comparison is between the Mytek Brooklyn DAC and Meridian's own Explorer2 with MQA firmware. With each DAC playing either the HDtracks download or streaming off "Master" TIDAL with "Passthrough MQA" for hardware decoding, in total, there were 4 recordings made in 24/192 resolution as below:

As you can imagine, with the different recordings, I can then run objective comparisons to determine how close the MQA decoded analogue output from the DAC is with the HDtracks download for each device. Plus I can compare the sound coming out of the DACs and see if there is a relative difference between whether the DAC was fed standard HDtracks data versus MQA.

Since we don't have an MQA-encoder available, let's try using a popular song for this comparison. We decided on using Led Zeppelin's "Your Time Is Gonna Come" from Led Zeppelin (1969, 2014 24/96 HDtracks, DR9). Note that I had already demonstrated with the track "Good Times Bad Times" previously that the TIDAL MQA stream is essentially the same mastering as the HDtracks download. We purposely picked another track from that album because the peak level for "Your Time Is Gonna Come" is the lowest on the album (-1.7dB peak) which provides some overhead protection to reduce intersample overloading when the DAC performs its usual digital antialiasing filtering whether natively or with the MQA parameters. Furthermore, this album lights up "blue" which means that it's "MQA Studio" authenticated, the highest level of authentication (the lower level has a "green" light).

So then, let's compare... First, comparing the HDtracks 24/96 download with MQA decoding to 24/96. As I did previously, I'll use Audio DiffMaker software to create the difference file from ~15 seconds of the song recorded at 24/192 starting at about 10 seconds into the tune.

Mytek Brooklyn DAC - HDtracks playback vs. MQA hardware decode off TIDAL:

Meridian Explorer2 DAC - HDtracks playback vs. MQA hardware decode off TIDAL:

Click on the waveform composite images to have a look at the details like the frequency spectral display plot and the averaged FFT of the "difference" file. Basically what we see in both the Mytek and Meridian DAC outputs is that indeed there is very little difference between MQA and HDtracks playback. The "Waveform display" is essentially a flat line, the "Frequency Spectral display" looks like low level background noise in the ultrasonic range, and the FFT spectrum shows a few noise peaks down at -80dB or so. As I noted in my previous examination of MQA, this is good I suppose... It basically tells us that MQA is generally able to represent a 24/96 HDtracks file compressed into the 24/48 "bit bucket" (remember, this isn't a true high-res album so any slight loss in noise floor due to MQA encoding below 16-bits or so is not an issue).

Now, let's see if we can do some inter-DAC comparisons!

HDtracks 24/96 playback - difference between Mytek Brooklyn vs. Meridian Explorer2

MQA hardware decoding - difference between Mytek Brooklyn vs. Meridian Explorer2

Whoa! Look at the differences now between the DACs. We see that this is comparatively much different compared to playing back an HDtracks file vs. MQA on the same DAC. No surprise, right? After all, we can't expect a US$2000 Mytek Brooklyn to objectively measure identical to a US$200 Meridian Explorer2. Remember that the Audio DiffMaker program does try to compensate for small sample rate drifts and will also compensate for differences in gain (average amplitudes were only around 0.1dB between samples). Clearly the timing differences in playback are beyond the default level of compensation I'm using. This is likely why you see that Moiré pattern in the spectral frequency plot; the timing between the DACs are slightly different, more than likely undetectable in a listening A/B test but when you overlay them, a "beat frequency" can be detected.

Before anyone freaks out about the magnitude of difference seen here, realize that this is the result of objective analysis using a very sensitive 24-bit ADC capable of detecting very minute frequency response differences, changes in low-level noise, and distortion - capabilities beyond the human ear/mind. Though the difference is measurably obvious, if I were to listen to the two samples in a volume matched A/B test, I would not bet much money on passing a blind test :-). For the record, unblinded on my main sound system (TEAC UD-501 to Emotiva XSP-1 to Emotiva XPA-1L monoblocks to Paradigm Signature S8 speakers), I thought the Explorer2 sounded a little brighter and vocals slightly forward compared to the Brooklyn with this track - which one is "better" can only be judged by the ear/mind of the beholder.

However, what is interesting is that the difference between the DACs playing back either the HDtracks or MQA data has remarkably similar RMS power. This observation tells us that despite whatever customizations MQA is doing for each DAC as it implements its "end-to-end technology", the playback isn't any closer between the Brooklyn and Explorer2 than as if they're playing the HDtracks file. Based on this observation, we can take one more step and try to compare the difference between the MQA vs. HDtrack differences! If the observation is correct, then there should be very little signal left over...

Yup. Very little sonic variance between the DACs between HDtracks and MQA playback. At a total RMS power level in the -60's dB, I can turn my headphone amp up to 100% while playing this and barely hear much of a signal above the noise.

Part III: Conclusion

In this example with an "MQA Studio authenticated" (blue light, supposedly "approved" in studio by the artist/rights holder) playback of Led Zeppelin's "Your Time Is Gonna Come", we see that:

1. The TIDAL MQA stream is clearly based on the HDtracks mastering. Very little difference with total RMS power down at -70dB over 15 seconds of music which is inaudible using both the Mytek Brooklyn and Meridian Explorer2 DACs. This is basically a confirmation of what was found previously but this time using actual hardware decoded analogue output rather than digital extraction from software-decoded TIDAL output.

2. Whether the MQA DACs played an HDtracks file or MQA, the sonic variation between them was about the same. There is no evidence that these two MQA DACs sounded any "more similar" or "more different" to each other when playing straight high-resolution PCM compared to hardware decoded MQA.

Ultimately, I think when we read about the "authentication" function of MQA, all they're saying is that the DAC "light" ensures that the signal is what was expected from the studio and presented for MQA encoding. It's like a CRC embedded in a ZIP file to check for errors. Realise that this is not the same as "bit-perfect" because a decoded MQA 24/96 output will not be exactly bit-perfect with the studio's 24/96 "master" PCM fed into the MQA encoder (the bit-perfect master would likely be the HDtracks 24/96 download). That's all authentication means from what I have seen.

I see no evidence that there is any special "authentic studio sound" that MQA decoding actually preserves or ensures. As you know, MQA's algorithms are proprietary and whatever optimizations they might have included in the firmware to make the Brooklyn and Explorer2 "certified" DACs (beyond money the companies paid to get the firmware done) did not seem to change the nature of the sound in a detectable way with the professional ADC. Putting it another way, there was no special "MQA voicing" found.

As far as I can tell, the more I examine this whole MQA "thing", the less I see evidence of any actual technology that improves overall sonic fidelity. It's an encoding technique that "encapsulates" some data for ultrasonic reconstruction (not really significant IMO) in the lower bits typically in the noise floor, throws in the indicator light for error detection ("authentication"), and uses a sort of upsampling filter. Claims of time-domain accuracy appear meaningless, and there's nothing so far to suggest that it brings us any closer to some concept of sonic standardization. This is not surprising I suppose, last year when I spoke of DSP room correction, I already suggested the meaningless of MQA's claims of "end-to-end" authentication because even if they did somehow ensure that MQA-certified DACs were calibrated to have similar tonal quality and accuracy (perhaps an analogy might be color calibration of TV sets), they could never ensure that the final sound is of a certain fidelity! MQA has no dominion over the effects of speakers and the sound room which are of course where the vast majority of distortions and tonal irregularities arise.

Note that I'm basing these observations on a single track (although "Studio MQA" authenticated). Although I only showed the results from one comparison point, I did have a look at another spot about 1 minute in to find similar results. Perhaps this Led Zeppelin album isn't fully representative of what MQA is capable of... Who knows. Maybe Meridian/MQA could clarify this with some objective results of what "major step forward in sound quality" they're talking about rather than just more words and innuendo. There are many obvious ways they can do this if they honestly want to "walk the talk".

Thanks again to my friend for "virtually" making available his gear and valuable time :-).

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In other news, I was reading this analysis of MQA from SoundStage! the other day. A few comments with quotations from the article as applicable:

1. "One is the claimed lossless compression of files of resolutions as high as 24-bit/768kHz to 24/44.1 or 24/48 (depending on the original sampling frequency), the results being files roughly 50% bigger than a 16/44.1 file."

Yes! Thank you for reminding people that the resulting file is actually bigger than a similar 16/44 FLAC lossless compressed file. Going from 16-bits to 24-bits with compression like FLAC usually results in around 50% increase, but in many cases, these MQA files are minimally compressible in those lower 8-bits where MQA data resides and results in >50% size increase.

2. "Since the process is claimed to be lossless, there should be no reduction in sound quality".

Remember, this is not lossless (ie. bit-perfect) as we normally think of lossless FLAC or ALAC. It's "partially lossy" as I noted last year - that's as certain as the Earth revolving around the Sun. So even though it's "claimed", we need to remember that at best this is "perceptually lossless" assuming that for the piece of music, the change in noise floor due to the embedded data isn't noticeable. We need to end the "claimed" provision and call a spade a spade.

3. Nice to see the audiophile press actually acting more like journalists and expressing independent thought! Kudos. However I must say that criticism of MQA began for me back in January 2015, way before the writer's article in April 2016 when Meridian started acting dodgy with their lack of A/B comparisons at audio shows.

Seriously folks, wasn't it obvious that what they were proposing had a strong ring of improbability to it even with the initial announcement back in late 2014? Are audio technology writers that out of touch with how things work that questions weren't asked right from the beginning? Maybe it's the lack of courage to swim against the tide of other publications? Or perhaps they were all under the influence of Meridian's fancy public relations party (check out this ridiculous video; "bought and paid for" comes to mind) at the The Shard in December 2014?

4. "I can’t confidently say that I’ve heard any differences. As a result, I’m sure that if I did a pseudo-blind test, as John Atkinson did, my results would probably be similar to his -- basically, the equivalent of guessing."

Nice. Again, about time an audiophile writer admits to this given the presence of obvious objective evidence. So what does one make of J. V. Serinus' claim in December 2014 that "I literally laughed at the difference when the MQA version began. Not only did it feel as though a veil had been lifted, with far more color to the sound, but instruments also possessed more body. With more meat on dem bones, I also noticed less of a digital edge on the violin. I've heard Hahn in concert several times, and this was the closest to real I've ever heard her violin sound on recording"? What kind of faith are we to have in subjective impressions like that? Did the company present a fair comparison for him? Does his hearing need to be checked? Was he caught up in the hype and excitement? Ultimately, would or should this kind of testimony have much affect on audiophiles at large?

Well folks, after years of pure subjective "analysis" and opinion-making with little facts, I honestly do hope that the audiophile hobby can come to terms with the importance of being rational. I believe it all has to become more objective and more rational in the days ahead for the sake of credibility compared to other technologically based hobbies. Perhaps we'll talk more about this another time soon...

Hope you're all having a great time enjoying the music! Happy Easter.