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MQA Deep Dive - I published music on tidal to test MQA

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pjug

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Great post, and I agree with the vast majority of it. Of course I have to nit-pick at least one point. IIRC, the space savings of MQA WRT 24/88.2 FLAC encoded PCM seemed of significance, hence the discussion of 20-bit 88.2kHz or 96kHz. But if we accept the market will not accept a 20-bit format, and if we accept that we need 26kHz of bandwidth for "high-res", then I have to wonder how well FLAC would compress 24-bit 88.2kHz or 96kHz PCM that had been aggressively filtered to a 26kHz pass band. And would it be any more disingenuous to market such content as "88.2kHz" or "96kHz" than it is to market MQA as "24-bit"?

Also, there is one important part of the discussion that I feel is missing from this, which is the fidelity of the 16-bit 44.1kHz MQA format (ie. the MQA-CD format) fully decoded and rendered vs. regular 16-bit 44.1kHz PCM.
If the MQA renderer is not 24 bit, why would another format have to be 24 bit to be accepted over MQA? Just keep the 24-bit container with a truncated least few bits and don't even talk about bit depth, just call it hi-res resolution and sampling. Not that I'm even looking for something like that; just don't replace redbook with something else and I'll be happy.
 

bennetng

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danadam

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More devils advocate: I wonder what what the effect on FLAC encoded file size would be of sign-extending 20-bit PCM to 24? Seems it would compress pretty well...
Same as setting LSB to zeros:
Code:
sox -r96k -n -b24 pink.24b.flac synth 10 pink norm dither
sox pink.24b.flac pink.20b.zero_LSB.flac dither -p 20
sox pink.24b.flac pink.20b.zero_MSB.flac gain -24.0824 dither

2'610K - pink.24b.flac
2'141K - pink.20b.zero_LSB.flac
2'142K - pink.20b.zero_MSB.flac
Or on a music track:
Code:
84'935K - 02. Mosaic.24b.flac
61'686K - 02. Mosaic.20b.zero_LSB.flac
61'514K - 02. Mosaic.20b.zero_MSB.flac
 

DimitryZ

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Dimitry, without slightest provoking, but why do you say that?

Yes, strumming an acoustic guitar will not produce too many high-energy overtones, and neither will a finest falsetto singer... Yet my son synthesizes square waves and triangular-envelope spectra (not decreasing but increasing with frequency triangular!) all the time - while composing music for his computer games with his friends (using FL Studio). Eg, listen to any modern [Nintendo] Mario game soundtrack - anything goes! The limit is only the human hearing, definitely not the sound source/origin. And we - or our kids - are definitely way past the 'old school', whether it's Mozart or The Eagles.
Maybe someone can FFT such game soundtrack and show what it looks like?
 

DimitryZ

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Thanks, you are actually making my case for me. :)

There are two rather independent statements going on: (1) "there is little ultrasonics in the 'music' " and (2) "humans can't hear ultrasonics"...

Personally, I absolutely subscribe to the second. So yes, my son and his friends cannot hear 35kHz.

However, when people say "The 'music' spectrum envelope follows the 'MQA triangle' - and this is how I interpret Dimitry's "ultrasonic content is very low compared to normal music in the baseband" - this is what I was trying to question/disagree with by referring to my son's electronic ['square-wave'] music synthesis experiments.

To reiterate, I agree that we should not care about ultrasonics in our music playback designs. But not for the 'significant vs insignificant [ultrasonic] proportion' reason - which in my mind (and in my examples) is questionable. But simply 'because humans just can't hear it'.
Didn't we seem to have agreed that "the triangle" is a rhetorical device?

You drew a plausible plot earlier, which showed two rectangles - one for baseband and one for ultrasonics, the latter much smaller in amplitude.

So MQA should be able to encode the entire LPCM baseband - no triangles.

However, it can't encode lots of ultrasonics, since there is little room in the baseband for hidden data.
 
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Raindog123

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Didn't we seem to have agreed that "the triangle" is a rhetorical device

Yep, by the triangle here I mean the downslope-shaped empirical ‘real music‘ spectrum envelope (or is it the average?) referenced by the MQA guys. (Not the triangular implementation of ‘unfolding’ that one might think of while following their concept explaining.)
 
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earlevel

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2. It creates reconstruction-filter challenges for playback equipment. Hopefully this will be solved more fully as time goes on, but as of now there are lots of DACs out there that either emit audible clicks when switching between MQA and non-MQA filters on the fly, or else just keep MQA fllters on permanently. As MQA filters are slow/leaky, they produce undesirable aliasing. If you can't turn them off for non-MQA content, or you can turn them off only at the cost of audible clicks between MQA and non-MQA tracks, that's a problem.

Nice post. On the one detail, of course, it's trivial in DSP to avoid the clicks. Surprising people put out gear with clicks.
 

DimitryZ

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Yep, by the triangle here I mean the downslope-shaped empirical ‘real music‘ spectrum envelope (or is it the average?) referenced by the MQA guys. (Not the triangular implementation of ‘unfolding’ that one might think of following their concept explaining.)
So perhaps electronic music with high volume content in their target "data band" - 16-20KHz will limit the amount of ultrasonic content MQA will be able to hide in such a file?

As an example, say you created a piece of abstract electronic music that sports full volume pink noise in the 16-20KHz AND high volume ultrasonics as well. This may very well a type of file that MQA will not be able to encode. But this may not be a practical limitation in the greatest majority of cases.
 
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Blaspheme

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So perhaps electronic music with high volume content in their target "data band" - 16-20KHz will limit the amount of ultrasonic content MQA will be able to hide in such a file?

As an example, say you created a piece of abstract electronic music that sports full volume pink noise in the 16-20KHz AND high volume ultrasonics as well. This may very well a type of file that MQA will not be able to encode. But this may not be a practical limitation in the greatest majority of cases.
Presumably, Autechre are on to it.
 

DimitryZ

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I actually think this enormous thread, especially the last several pages, has produced some very helpful clarity despite the periodic acrimony.

That clarity comes in a very particular area: the entire debate about whether "real music" contains high levels of ultrasonic content is a debate that has arisen because of the fundamentally questionable claim at the heart of MQA's design. That claim is the claim that true high fidelity music reproduction requires a sample rate greater than 48kHz, because according to Stuart (in his AES paper), digital hi-fi music reproduction requires bandwidth up to 26kHz.

So is @Raindog123 correct that "real music" includes electronic music that can have increasing amplitude as frequency increases up to and beyond 20kHz? Yes, that appears to be correct.

Is @DimitryZ correct that generally speaking music produces ultrasonic tones at lower amplitude than tones in the audible band? Yes, that appears to be correct as a general proposition even though there are exceptions per Raindog's comment.

Is @amirm correct that if you are going to create, market, and distribute high-res music, then you have to deliver it in 24-bit form since 16-bit is the next practical step down from that, and that you more or less have to deliver it in at least 88.2k/96k form since 44.1k is not high-res and 48k is not consistently considered high-res by audiophile consumers? Yes, he is correct about that. We here can certainly critique that audiophile conventional wisdom, but Amir is basically correct about those market realities in terms of the available tiers of bit depth and sample rate.

Are Amir, @John Atkinson , and Bob Stuart correct that a fully "empty"/"100% clean" 24 bits of depth is not necessary to produce a sufficiently low noise floor that meets or exceeds the limits of human hearing? Yes, they are correct. While Amir's, Atkinson's, and Stuart's particular arguments about this have some slight variations from each other, we can all acknowledge that 6.02 x 20 = 120.4, which means that 20 bits' worth of depth provides the necessary -120dB noise floor and therefore it is not necessarily a problem to store data in the lowest 4 bits, if there is some value or good reason to do so.

So none of these arguments is, in my view, wrong - they are all substantially correct as far as they go.

The underlying issue, of course, is that there is no evidence that ultrasonic frequencies are necessary at all - at whatever amplitude - for hi-fi music reproduction. And since there is no need to preserve ultrasonic frequencies, there is by definition no sonic value in doing anything - no matter how clever or allegedly harmless - to store them inside the digital data that encodes/stores the sound in the audible band. In other words, the way to reduce the file/bandwidth size of high-sample-rate digital content without compromising fidelity is simply to downsample it to the minimum feasible sample rate whose Nyquist frequency remains above 20kHz (plus some buffer for filtering).

So a lot of the stuff we've been arguing about doesn't actually need to be argued. The only real question from a sonic point of view is:
Is there potential harm caused by the way MQA stores ultrasonics and other encoding info/data/flags in digital files? I would say Yes, for two main reasons:
  1. It stores some of that data within the first 16 bits. That means decoded, 24-bit MQA may have compromised bit depth because its effective bit depth is not contiguous in the most significant bits. It also means that undecoded MQA has a noise floor inferior to 16-bit redbook, which is a problem not only for the millions of playback systems that lack MQA capability, but also for the fact that undecoded MQA content has begun to pollute the pool of redbook digital music, and if/when undecoded MQA files begin to circulate outside Tidal (very likely/possibly already happening, because we know how lazy/indifferent the labels are about this stuff), they will not be marked as such and we'll have no way of knowing where they are or how numerous.
  2. It creates reconstruction-filter challenges for playback equipment. Hopefully this will be solved more fully as time goes on, but as of now there are lots of DACs out there that either emit audible clicks when switching between MQA and non-MQA filters on the fly, or else just keep MQA fllters on permanently. As MQA filters are slow/leaky, they produce undesirable aliasing. If you can't turn them off for non-MQA content, or you can turn them off only at the cost of audible clicks between MQA and non-MQA tracks, that's a problem.
IMHO the market case for MQA is very limited and rather weak. There is no significant streaming (or IMHO digital-file-for-purchase) demand specifically for files with bit rates above 88.2/96k. And MQA provides no significant size savings compared to 24/88.2 or 24/96 FLAC. Moreover, the ability to have one MQA file that can be served in multiple resolutions is also a highly overrated feature, since in practice that "multiple" is only two: redbook and high-res. There is no market for - and never will be a market for - a more split-up set of tiers like redbook vs 24/48 vs 24/96 vs 24/192, etc. Never going to happen.

In this vein, one can make a strong argument that the main - and only significant - force working to create a market for super-high sample rates like 352.8k these days is MQA itself, which is ironic since MQA does not deliver that sample rate and is totally incapable of ever doing so.
Very good post.

Should we spend some more time on the topic of design intent?

I understand the position that ultrasonic content is unnecessary for consumer distribution format. However, if one takes that position and looks at the three main formats that can be purchased by the consumer (Hires LPCM, DSD, and MQA), surely the first two can provide essentially unlimited ultrasonic content. At the very least, MQA limits this to near ultrasonics, that are, at least theoretically, musically related.

It would seem that making rational choices as to how much ultrasonic content to provide to the perpetually bit and Hz hungry audiophile community is actually a good thing, philosophycally speaking?
 

RichB

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This is both the rule at Stereophile and general journalistic practice.

John Atkinson
Technical Editor, Stereophile

That may be and could be a reason to disregard data from unverified sources.
However, if an issue can be reproduced and ignored, that would be bad right?

- Rich
 

RichB

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You have no case with me there. I have the same beef with Archimago. If he wants to be authoritative, he needs to use his real name. Objectivity needs to apply to him as well. People examine my background all the time in judging what I write. Why should Archimago be exempt? It was a mistake for Chris to use him as an expert witness while he was using an alias. Still is. So don't bring this argument to me. I am firmly on the side of full disclosure when it comes to people in the public/industry. Have always used my real name and will continue to do so.

Archimago's Musings: MUSINGS: On the RMAF 2018 MQA talk, pseudonyms, and the right to anonymity.

MQA_Bruno_Mars_-_Imaging.png


I trust that most audiophiles can look at that FFT and realize that there's obviously something not right about that graph. Does it matter if my credentials included a PhD in astrophysics, or if I trained as an audio engineer, or if I served burgers at the local McDonald's? When simply by using free tools while streaming Tidal and some basic knowledge of Adobe Audition (or free Audacity for that matter), anyone can find that abnormality?! (As Chris stated, in fact, the issue was already posted on YouTube almost a year before my article. And here I see Chris made a video himself.)

As I recall, it was not the town PhD rocket scientist who called out "the Emperor has no clothes!"

At 11:00, Chris basically said as much - "This can be reproduced by anyone with the requisite skills". But that's of course not good enough for Mr. Forsythe - "I just want to know who he is and what his credentials are for producing this..." Honestly guys, the image above is one of the easiest anomalies to find and I'm sure those guys can just ask Bob Stuart if they really don't know why certain songs demonstrate that behaviour! Måns Rullgård's work exploring MQA's "rendering" function I'm sure took him many hours of combing through the code and creating his decoding tool. Capturing the various impulse responses, dithering, noise shaping likewise was more involved than having a look at Bruno Mars' song.

Maybe there's a point for Mr. Forsythe to suggest "... it would be interesting to know if this is a competitor looking to come up with something smart or clever(er) than what we have, or is this an individual, or is this somebody clever with Photoshop." As has been said many times, I am not a member of the Industry. But even if I were, so what? It doesn't explain or excuse what is found and how the findings contradict claims of "the exact studio sound" - the point that Chris was making when the image was shown.

Then there's the question of "Has anybody else reproduced what he's produced?" (Of course others have... and yet again "Why won't you release his name?"). At 14:20, Forsythe made the "anonymous source" comment. I'm glad someone mentioned that he can just come to the blog here or send me a message on the audio forums I visit if he wants to talk. Bravo to the audience member.

This appears to be real music with missing data surrounding 22 kHz.
I have seen many attacks on the Archimago but no direct comment on the data.

- Rich
 

RichB

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False marketing breaks nothing except promises. The actual products may work to a high standard. They do not break when the marketing dept lies.

It is disingenuous to suggest otherwise.

If marketing makes false statements, then counter programming is required.
It's hard to trust the engineering when the marketing lacks integrity.

- Rich
 

RichB

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On the other hand, if I am mistaken and MQA CDs/16-bit MQA files put some or all of those ultrasonics in those lower 3 bits, then that makes it even worse because it only adds to the non-random quality of the noise in those lower 3 bits, further degrading the effective noise floor/bit depth.

Regardless, this diagram is a nice illustration of MQA's underlying conviction: MQA is based on the claim that it is worth reducing the unmolested bit depth by 3 bits/18dB in order to preserve low-level ultrasonics. Personally I don't see that as a worthwhile tradeoff.

If MQA encoded streams are appearing at 44.1/16 bits, then such a format has very little justification. I believe this was posted on this enormous thread, during its first lifetime.

- Rich

Also: Free @mansr :)
 

RichB

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Well, whatever you build also needs to have a complicated story so audiophiles can't understand it just like MQA and believe you are producing 24 bits. ;):)

Complicated is fine. Provably false, not so much.
Let's not rehash the lossless thing again and the plainly false marketing. That is well established.

- Rich
 

RichB

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Here is the MQA-CD web page: MQA-CD
MQA is now available on CD, allowing any CD player to deliver more detailed, nuanced playback. When paired with a decoder, MQA-CD unveils the full master quality recording, just as it sounded in the studio.

Technically, if the master is recorded at > 44.1 kHz and 24 bit, this statement is clearly false.
It safe the say the mastering engineer producing the desired sound without MQA.

If MQA did not alter it, the it would have the same dynamic range and frequency response as a RedBook CD.
This is clearly false since bits of fully audible potential dynamic range has been consumed.

Of course, MQA could sound the same, so it was pointless.
If MQA sounds different, then they have violated the mastering engineers intent.

Perhaps, in MQA classic form they have moved away from the "intent" into the sound in the studio, which of course is meaningless for music mastered with headphones.

Steve Guttenberg makes this point very well.


- Rich
 
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