MQA technical analysis

[Jud]

I fail to see the point of any of it.

 

That's because you are blurry and need de-blurring.

[Jud]

As a matter of mathematics the two are interchangeable, so strictly any inaccuracy in one domain must mean some sort of inaccuracy in the other.

 

So "fools rush in," but:

 

Since the relationship of time domain and frequency domain accuracy is that of conjugate variables, wouldn't inaccuracy in one domain increase or decrease opposite to inaccuracy in the other? Thus Fokus' description of allowing frequency domain inaccuracy (aliasing) to some extent that is hopefully masked, in order to allow what is thought to be better time domain accuracy (I suppose intended for the sake of transients, percussion, instrumental and vocal attacks - all the inharmonic stuff).

[Jud]

The crux of MQA, when dealing with original rates in excess of 96k, is to allow aliasing, but within limits. Particularly in the baseband the filters are tuned so that the aliasing there does not exceed the programme's innate noise or another suitable masking threshold. In the 24-48kHz band the situation is more dire.

 

So "the situation is more dire" where most of the recorded music is?

[Jud]

Please read again.

 

My music does not reside in the 24-48kHz band. Maybe Batman's does?

 

Oh, I was thinking of sampling rates.

[Jud]

-this whole transient accuracy thing should be demonstrated by reference to actual musical events not dirac pulses.

 

Certainly.

 

...if our senses were disturbed by timing uncertainty at that level I don;t think anyone would ever have liked LPs.

 

 

LPs - how many people now say they hear the distortions in comparison to digital? Almost as if we'd trained ourselves to ignore the distortions by long exposure....

 

Fascinating topic, but I don't want to get off the subject of what we're able to learn about MQA.

[Jud]

Indeed, the idea with digital audio is to place the Nyquist frequency above the audible range. The CD standard assumed an upper limit to audibility of 20 kHz and allowed ~2 kHz for the filter transition band. Now audiophiles argue that higher frequencies are in fact audible in some way or other and must thus be preserved.

 

I couldn't hear squat above 16KHz a couple of years ago and it's probably lower now. I'm assuming aliases will cause no audible harm to anything I'm listening to unless those above 16KHz cause harmonic or intermodulation distortion at audible levels in lower frequencies.

 

Any indication MQA might do harm in this way? Or in some other evidently audible fashion?

[Jud]

It is clear that MQA causes a lot of aliasing. Why take the chance?

 

If it did something else better, I suppose.

 

Anything else pop out to you as something it's doing wrong that might be audible? I'm assuming the dither noise is (virtually by definition) very low level, and that the 8KHz packet noise Miska noticed also should be at lower than audible levels. Might either of those assumptions be incorrect?

[Jud]

I'll tell you what would be better. Not mucking about with sampling rates in the first place.

 

Having somewhat covered the "Is it doing harm?" topic, time to go on to "Is it doing any good?"

 

Any benefit in terms of ringing, if you can tell from what you've done so far?

 

 

Edit: Sorry, I should be more precise - any additional benefit beyond the old Meridian filters, or does MQA look pretty much like Meridian repackaged in that regard?

[Jud]

Compared to what? Compared to leaving the original untouched, it's obviously doing no favours.

 

Apologies, see my edit.

[Jud]

Anything that has distortions, no matter how euphonic, cannot be described as improving accuracy.

 

Or more accurately ( ) and specifically, since everything has distortions: MQA, assuming they were trying to make sense (bear with me), would have to be saying they reproduced the signal less accurately in one or more less audible aspects for the sake of improving accuracy in more audible aspects.

[Jud]

For accurate reproduction, every harmonic instrument creates needs to be recorded and reproduced.

 

 

Though very few speakers (headphones?) will reproduce most of that range. But it probably isn't a good solution to create problems further up the chain.

 

There is another school of thought that says this is exactly the problem with hi-res: 44.1 captures all the audible effects of intermodulation with ultrasonics that occurred during the recording, so using higher rates is just asking for trouble.

 

This is very interesting stuff to me, so I can't help talking about it, but I must also once again thank mansr for his good, focused work in explaining exactly what MQA *is*.

 

 

Sent from my iPhone using Computer Audiophile

[Jud]

The Amazon link for, say, the RME Fireface appears regardless of what is said about it in the text. In fact, you often see these content-related ads pop up in the most ironic of situations, i.e. right next to a scathing criticism of whatever the ad is for.

 

Which situation has no effect whatever, I'm sure, on a desire to drive traffic by developing a reputation for publishing said scathing criticisms. (Eyebrows raised.)

 

 

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[Jud]

The point is that to Amazon and Google your opinion doesn't matter. They'll find an ad to show no matter what you write. When you deal directly with the advertisers, they have a lot more leverage in that they can simply stop running ads on your site if they don't like your writing. If you rely on them for your pay cheque, you just might be tempted to keep them happy.

 

While obviously any income-generating site has an incentive to stay popular, pandering to advertisers isn't necessarily going to help with that. Clickbait and sensationalism works quite well, but those don't imply any particular bias.

 

Trying to place Archimago in the same basket as Audiostream et al just because he has a few syndicated ads on his blog is pathetic.

 

Why, exactly? You have just noted sensationalism works well; I'd add to that anything, really, that tends to make someone other than run-of-the-mill. Middle of the road need not apply. So either mythmaker or mythbuster.

 

Publications regarding the high end audio industry tend toward excitement and enthusiasm for the product. If you wish to read payola into that, it's your prerogative, but frankly I doubt any such thing is really necessary to get people who are "into" audio and love to write about products to sound enthusiastic. That space is already well covered.

 

So any individual who wants to drive traffic better look at another market segment, and Archimago has one. I don't think he needs to change what I assume are his natural skeptical tendencies to write what he does, any more than I believe journalists for the magazine sites need to change what I assume are their natural mostly enthusiastic tendencies in order to write what they do. I attribute nefarious motives to neither. A desire to drive traffic? Of course. Who wants to run a business to lose money?

[Jud]

We've all seen the characteristic noise hump in undecoded MQA files. Apparently, this is the result of shaped dither applied during the encoding. The first two steps of the decoding process entail removing part of this noise. This is possible since the pseudo-random sequence used to generate it is known. Here's a graph of the decoder in action:

 

[ATTACH=CONFIG]33109[/ATTACH]

 

Is essentially all of this taking place in the last one/two/few LSBs?

[Jud]

The low 8 bits of a 24-bit MQA file contain a compressed representation of the 24-48 kHz frequency content. The decoder combines this with the base band information in the high 15 bits to recreate a 96 kHz stream. This part works more or less the way they say it does.

 

The claim comes from looking at the actual code that does it. It's a perfectly standard polyphase interpolation filter. Nothing more. The filters they use have horrible amounts of aliasing/imaging, which is why the output includes frequencies above 48 kHz.

 

 

Not having any technical understanding, I'm wanting to know whether or not the output includes frequencies above 48KHz because that's needed as part of the 96KHz recreated stream. A simple arrow flow chart (A -> B) of the sequence of the filtering and "unfolding" would be helpful to me, I think.

[Jud]

Can we drop that topic in this thread? Please.

 

Yep - Samuel, that's been moved to a dedicated MQA and DRM thread.

[Jud]

MQA filters are specifically extremely non-sharp and "poor", so they leak a lot.

 

 

 

Are they poorer in this regard than any (meaning all) of Meridian's non-proprietary filters?

[Jud]

Sorry but I don't understand the question, what do you mean by non-proprietary?

 

The earlier Explorer (non-2) was better in that respect:

[ATTACH=CONFIG]33144[/ATTACH]

 

Or if you look at the original Prime:

[ATTACH=CONFIG]33145[/ATTACH]

(possibly changed later as part of MQA firmware update?)

 

Sorry, Stuart and Craven's non-MQA filters would have been a better way of putting it - but you answered in any case.

 

 

Miska, your images are showing as non-valid attachments.

[Jud]

LOL.

 

OMG Chris, I have "commercial interests"? Come on man... The amount of traffic I have on the blog *pales* to the commercial interests on any of the major audiophile blog and sites I've seen. To put it another way, I make a few bucks off Amazon if there's anything I talk about and readers buy, and another few bucks in AdSense. Notice that not all my posts are about audio, some about video as well; stuff that interests me and experiments that other hobbyists might find interesting.

 

Let me be honest as well. I make more money in my day job in one day than 2 years worth of what I'm getting off blog proceeds... I trust this puts into perspective the level of "commercial interest" I have.

 

I'm interested in truth. I'm interested in having audiophiles be educated in such truth as can be proven with evidence. Not every audio lover will care about a lot of this but I do want the material and measurements out there for reference if one days, an audiophile get to thinking about an alternative viewpoint other than the interests of the "mainstream" audiophile Industry-supported media.

 

Go ahead and do the same with your reviews by adding objective data and I will be a happy man because then I can look forward to answers rather than yet more testimony and opinions rather than facts. I would happily retire when that day comes!

 

I like being able to see the measurements and other information on your site, and other similar information here. They are very often very helpful.

 

I do happen to think better understanding leading toward what can objectively be called progress will actually come not solely from what you are referring to as facts, but also to some degree (it might be small, but some) from what you are referring to as "opinions" and "testimony." There are some things at which human perception is very bad in comparison to technical means of measurement, but yet there are certain areas where human perception is as yet superior to anything technology can provide. I think we ought to make use of each in its areas of superiority.

[Jud]

While I agree with what you're asserting here, I still think we're not addressing the "business reality" and how a successful "business" with regards to "audiophile social media" pretty much depends on an overall favorable opinion from the vendors. Based on what I've seen on his blog, Archimago is not bound by that "red line" where perhaps Chris is.

 

When a certain other Audiophile Social Media Personality swaggers in here to take others to task, the clear motivation is to "protect" his business.

 

My point is that if there is a line between pro-vendor and pro-consumer in audiophile social media, it's not possible to make a successful business without being on the pro-vendor side of that line, period. Archimago is clearly on the pro-consumer side of that line, and has accepted the reality that he will not be rewarded by "business success" as a result. This clearly gives him a level of freedom that often invites scorn and even envy from some quarters of audiophilia.

 

I disagree that Archimago should consider subjective testimony when conveying information to his readers. There's far too much of that in the mainstream audiophile press and social media and it would only invite mistrust from his readers.

 

Since this is OT in a valuable thread, I'll make a quick reply and we can take it to another thread to discuss further if required.

 

I do not think this divides neatly into pro-consumer and pro-industry. I, along with many other consumers, appreciate some opinions and testimony. I also see industry marketing geared toward consumers who think of themselves as objectivists.

 

I'm not questioning anyone's motives (I think there's far too much of that in our discourse as it is), simply saying opinions can be informative and measurements can be used by manufacturers as marketing.

 

 

Sent from my iPhone using Computer Audiophile

[Jud]

That sounds like a standard apodising filter. Nothing novel about that. Anyone can do it.

 

It has been a while since I read the patent and white paper. Was there something about a windowing function (doesn't mean they're currently employing it)?

 

 

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[Jud]

But with existing recordings they claim upon encoding to be removing or lessening preresponse "blur" caused by processes such as sample rate conversion by delaying it relative to the response. Is this the same as using an apodizing filter on a DAC upon playback?

 

There are well known techniques for removing ringing, at least one of which MQA appears to be employing currently, apodizing filters. By all indications, those they're using appear to prioritize subjective "excitement" over what is generally considered accuracy.

 

 

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[Jud]

I am a little surprised to see so much discussion of the basic nature of the MQA DSP even after the response graphs, but will chalk that up to my knowing so little as not to realize it is still very early days in this technical analysis. Let me see though as I try to follow whether this is accurate:

 

- If filters ring, they will do so at a relatively sharp cut point, if there is content to cut. So for 24/96 material, if the filter has a sharp cut at 48K and there is content at 48K and above, it will ring. (At the moment let's leave aside phase and pre vs post ringing.) Same for 44.1K rate material and a filter that sharply cuts at 22.05K, and etc.

 

- Apodizing filters don't cut sharply, in order not to ring themselves. So they must start sloping gently well below the frequency of any ringing in the content they receive in order to remove that ringing (well below 22.05K, 48K, or whatever the relevant frequency is).

 

- Has it been determined at this point that the MQA filters cut so little they won't remove any ringing in the content they're given?

 

- I'm not catching Fokus' point about what this implies for the encoding, and hope it can be explained in a little more detail.

[Jud]

1 minute ago, mansr said:

I have spotted filter 11 in the wild. Stay tuned.

 

Sounds like the comments pages of Audubon Magazine.

[Jud]

3 hours ago, mansr said:

You wouldn't need an MQA DAC. I could do the rendering in software.

 

If you can then convert it to DSD256 without monkeying with the minimum phase....

 

I don't know what's in MQA besides my memory that I liked Joni Mitchell's "Blue."  (Felt that I liked it slightly better non-MQA.)

 

In fact if you could do three files, MQA, non-MQA with minimum phase filtering, and non-MQA with linear phase filtering, all converted to DSD256, that would be just about perfect.  If you don't like Joni, anything sparsely produced, with vocals, acoustic guitar, perhaps piano, would be nice.

 

Just my tuppence.