Stereophile Series on MQA Technology

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3 hours ago, MikeJazz said:

Maybe the point of MQA, after all, is improving resolution of low and mid-fi systems??

A chain does not get stronger if you swap out a strong link while keeping the weakest links.  When I listen to music using my phone played on my car stereo I just use 192kbps mp3.  Why bother with anything better on a crappy sound system?

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1 hour ago, mansr said:

Yes. It's simple maths.

Explained here:  http://science-of-sound.net/2016/02/time-resolution-in-digital-audio/

"By the way, the samplerate doesn’t even show up in the equations!"

Bob Stuart even says this is not what he means by temporal blur, although I'm not sure what he does mean.

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1 hour ago, Fokus said:

There is not a shred of evidence that this so-called ringing, once it appears outside of the audible range, has any impact on perceived sound quality.

You have to shake your head when they dismiss their own experience with linear phase:  "One of the key notions on which MQA is based is that our ear/brain system regards pre-ringing as unnatural—and there's plenty of it here. And yet, the DAC3 HGC is a brilliant-sounding DAC."

He also writes "This is not MQA's claimed deblurring. Deblurring, per MQA, is the removal of time-domain artifacts remaining from previous analog/digital conversions;" 

So why so much talk about pre-ringing?

 

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4 hours ago, Miska said:

 

Filter that doesn't filter anything (all-pass filter) certainly has "perfect" time domain response.

As a few posters pointed out in the comments, using the term "ringing" gives a negative impression, when in fact some ripple is required for reconstruction.  If ringing is bad then long ringing is worse, and pre-ringing is even worse than that.  Many who know better seem to be perfectly happy to allow this misunderstanding to go on or even encourage it.

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I am not meaning to insult anyone but I think it is funny that in my head I have been hearing "GUTB" as

 

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Back to "MQA Tested, Part 1"...

Here is the response of the linear phase DAC, when input is MQA encoded impulse:

Fig.4 Benchmark DAC3 HGC, impulse response (one sample at 0dBFS, MQA-encoded, 48kHz sampling, 100µs/horizontal div.).

 

1. Jim Austin writes "This response is mostly linear-phase, though the asymmetry suggests some nonlinearity in the phase response."  WTF is "mostly linear-phase"?  Wouldn't it be more honest to say the response has lost the linear phase symmetry while at the same time retaining the pre-ripple?  In other words it looks kind of f'd up?

2.  Why didn't he show the response of the minimum phase and slow roll-off filters to the MQA encoded impulse?  I don't see how it could be an oversight that these were not included.

3. Can the people on here who are much smarter than me figure out how what modification MQA is making to the impulse such that it that would result in the response shown in Figure 4?
 

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4 hours ago, Rt66indierock said:

The current buzz word for MQA supporters is elegant.

This is hilarious.  I haven't seen this - do they say how they find MQA to be elegant or do they just throw out the word because it sounds nice?

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9 minutes ago, John_Atkinson said:

 

Maybe the word sounds nice to you, I don't have an opinion on that. But MQA's approach to digital audio
data encoding, reducing all the stages between the input of the A/D converter to the output of the D/A converter to a transparent "pipe," was a back-to-first-principles approach that I found elegant in the extreme. YMMV.

 

See https://www.stereophile.com/content/ive-heard-future-streaming-meridians-mqa

 

John Atkinson

Editor, Stereophile

 

I don't see how either of the bolded points are true.  BTW technology does not have to be elegant to be good or even great.  But MQA does not strike me as elegant, for  reasons Archimago has listed.

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23 minutes ago, GUTB said:

The concept of building a controlled end-to-end music consumption cycle that links the mastering engineer, commercial distribution and the end consumer playback system via a single technology solution is, in fact, elegant.

I am not talking about a concept; I am talking about the nuts and bolts of the technology, at least what I understand of it.

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On 12/16/2017 at 6:17 AM, mansr said:

What we're seeing here is the convolution of the linear phase filter with something that isn't a simple impulse. The honest thing would be to provide those test files for all to look at in whichever way they choose. Obviously, that's never going to happen.

 

Yes it seems that the MQA encoded test signal is quite different from an impulse. There is a manufacturer comment that was posted: https://www.stereophile.com/content/mqa-tested-part-1-manufacturers-comment 

I am wondering what some of you make of this.  The test input is shown there and below.

Bob Stuart comments:

"If we look at the 48kHz MQA test signal waveform (fig.1 in this comment), there is no pre-response. It is elegant that the decoder "unfolds" it back to a perfect impulse as we can infer from Jim's fig.5. Fig. 4 shows us the convolution of the signal with the linear-phase response of the particular chosen DAC (which is contributing the pre-and post-ringing). The result, as would also be the case with non-MQA files, will be different with other converters, according to the filter type (linear- or minimum-phase), rate and user settings." 

 

Fig.1 MQA-encoded impulse response sampled at 48kHz (50µs/horizontal div.).
 

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If this is the test signal, shouldn't it be a digital series?  Why does Stuart present it as an analog waveform?  Am I misunderstanding what he is saying?

 

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15 hours ago, mansr said:

That looks a lot like the impulse response of filter 7 in the MQA renderer.

Yes, I misunderstood.  I should have paid more attention to the caption of Bob Stuart's Figure 1. Stuart is showing the 48kHz sampled response to the MQA encoded test signal.  Whereas Jim Austin's Figure 5 is the fully unfolded 96kHz response.  Sorry to have added to the confusion with my misunderstanding!  And so it seems we remain are in the dark regarding the MQA encoded test signal.