Article: MQA: A Review of controversies, concerns, and cautions

[beetlemania]

On 3/16/2018 at 8:50 AM, Archimago said:

Yeah, the Ayre "Listen" minimum phase and slow roll-off filter was not something I liked with my PonoPlayer.

 

Interesting. The similarity between Ayre's "listen" and MQA is a reason I'm willing to give JA some leeway regarding his comments about SQ. The Ayre filter sounds really good to me and I prefer it to the "measure" filter. FWIW, I've been using first-order Thiel and Vandersteen speakers since 2002, maybe that makes a difference when listening to a minimum phase filter? YMMV. If I understand correctly, the leakage issue with the Ayre filter goes away at higher sample rates.

[Fokus]

3 hours ago, botrytis said:

I agree with Archimago. Until we know what 'deblurring' means to MQA (aka Stuart), we can guess until the cows come home. 

 

Deblurring is about getting rid of any filters with visible ringing in their impulse response.

[Norton]

2 hours ago, Archimago said:

 

Hi Norton,

With MQA decoding, they could potentially recover a little more of the original bit depth.

 

As shown above with that Buno Mars sample in the article, we also see the "leaky" filter at work.

 

 

Thanks, that suggests when playing a 48kHz MQA master, there wouldn't be much audible difference whether played via an MQA decoder/DAC  or not.  Unfortunately my Tidal trial is finished so I can't compare  myself.

[T.S. Gnu]

On 2018-03-07 at 12:58 PM, John_Atkinson said:

 Forgive me but I didn't say anything like that. If you go to my comment as moderator at

https://www.stereophile.com/comment/573060#comment-573060

you will see that T.S. Gnu wrote: "A rational viewer might question your opinion on who is trolling and who is being trolled." to which I responded: "Please refrain from posting argumentative statements like this. I have deleted the messages that followed this posting of yours as being an exchange of insults."

 

Which they were. No mention of banning.

 

John Atkinson

Editor, Stereophile

 

Mister Atkinson,

 

I find it interesting that you chose not to delete the comments I had been referring to with that comment — containing the words "back to school" which I have linked to for your edification:

https://www.stereophile.com/comment/573037#comment-573037

https://www.stereophile.com/comment/573039#comment-573039

 

Because of that omission, it is disingenuous of you to label my posts as insulting and argumentative while at the same time you allow posts containing "Until you reveal who you really are your accusations carry zero weight. And don't forget, I'm a customer and I don't like you." and beginning with "You should consider going somewhere else..." (I refer you to: https://www.stereophile.com/comment/573035#comment-573035 and https://www.stereophile.com/comment/573039#comment-573039) to stand at the same time.

 

Being the target of those posts, I find it offensive; both the posts as well as the inconsistent moderation, especially in light of the fact that I have responded with equanimity and reason to slurs and invective on your forum while you have entitled moderating my observational comment with "Flame Wars."

 

While the comment by botrytis was incorrect in its reading of your actions.

https://www.computeraudiophile.com/?app=core&module=system&controller=content&do=find&content_class=forums_Topic&content_id=38700&content_commentid=792085

it does not take away from the fact that you inconsistently singled out my comments insulting and argumentative.  It does not leave a reader with a pleasant taste or mouthfeel, I am disappointed to say. 

 

That aside, so keep up your good work. I am eagerly awaiting the articles you promised on deblurring and other aspects.

 

Regards,

T.S. Gnu

[T.S. Gnu]

On 2018-03-14 at 4:40 AM, John_Atkinson said:

 

Thank you for the link. Note that the articles in The Economist's "1843" magazine are published with bylines, in this case a Jennifer Brown.

 

John Atkinson

Editor, Stereophile

 

And...being a chartered forensic and occupational psychologist (https://www.economist.com/blogs/prospero/2013/11/quick-study-sexual-violence-britain) qualifies her to comment in this...how? Because the viewpoints coincide with yours? You appear to be implying that you would rather trust the veracity of an article on geology by a flat-earthen or YEC as long as they attach their name to it instead of a fact-filled one without a by-line. Interesting. Hmmm?

[T.S. Gnu]

On 2018-03-12 at 6:37 AM, The Computer Audiophile said:

....

This article is objective. 

 

2+2=4 no matter your name, pseudonym, etc...

 

If someone thinks this article doesn’t add up, then prove it wrong. Make a fool of me for standing up for the author and using my name as a guarantee to the CA community.

 

I’ve co-signed this loan and have no worries about creditors coming my way. 

Mister Stuart compared himself to Copernicus a while ago (Last para of article: http://www.theabsolutesound.com/articles/meridians-master-quality-authenticated-the-interview/). Sadly his following comment ("I guess I’m luckier, because the worst we’ll get is the wrath of audiophiles and scientists, not excommunication.") fearing excommunication further indicates fluidity with facts; Copernicus wasn't, and couldn't have been, excommunicated because his work was published after his death.

 

Having read this post, if I may be so bold, I would suggest you walk down the beach and think, "Now I know what Martin Luther felt." After all, this is addressing indulgences in a way. One could also say you could guess you will be luckier, because the worst you’ll get is the wrath of audiophiles and non-scientists, not excommunication. And you might be right because he, on the other hand, was excommunicated.

 

Irrespective of how this shakes out, history will view favourably the fact that issues were allowed to be discussed on this site free of dogma and preconception with intelligence not viewed as some hideous affliction. 

 

As to the question of anonymity that Mister Atkinson, Mister Stuart and their ilk bring up, it is perhaps respectfully fitting to quote a true follower in the steps of Copernicus:

"In questions of science, the authority of a thousand is not worth the humble reasoning of an individual." Galileo

[Archimago]

1 hour ago, T.S. Gnu said:

Mister Stuart compared himself to Copernicus a while ago (Last para of article: http://www.theabsolutesound.com/articles/meridians-master-quality-authenticated-the-interview/). Sadly his following comment ("I guess I’m luckier, because the worst we’ll get is the wrath of audiophiles and scientists, not excommunication.") fearing excommunication further indicates fluidity with facts; Copernicus wasn't, and couldn't have been, excommunicated because his work was published after his death.

 

Having read this post, if I may be so bold, I would suggest you walk down the beach and think, "Now I know what Martin Luther felt." After all, this is addressing indulgences in a way. One could also say you could guess you will be luckier, because the worst you’ll get is the wrath of audiophiles and non-scientists, not excommunication. And you might be right because he, on the other hand, was excommunicated.

 

Irrespective of how this shakes out, history will view favourably the fact that issues were allowed to be discussed on this site free of dogma and preconception with intelligence not viewed as some hideous affliction. 

 

As to the question of anonymity that Mister Atkinson, Mister Stuart and their ilk bring up, it is perhaps respectfully fitting to quote a true follower in the steps of Copernicus:

"In questions of science, the authority of a thousand is not worth the humble reasoning of an individual." Galileo

 

Hey there Mr. (I presume) Gnu!

 

Gotta say, I love your thinking, writing style and historical references! [I know, these are not 1:1 correlations but I get the point .]

 

Disturbing to even think anyone would use some of these historical references (like Copernicus) to describe one's own predicament around what MQA is about. That in itself IMO reflects an unwise level of self inflation.

[miguelito]

1 hour ago, T.S. Gnu said:

Mister Stuart compared himself to Copernicus a while ago (Last para of article: http://www.theabsolutesound.com/articles/meridians-master-quality-authenticated-the-interview/). Sadly his following comment ("I guess I’m luckier, because the worst we’ll get is the wrath of audiophiles and scientists, not excommunication.")

Stupid. Full of BS and thinks noone will notice. The initials spell it out!

 

And BTW, I am pretty convinced that there's a lot of EQ in all of this MQA nonesense... Add sugar and salt, it'll taste better. Jeezzz...

[WiWavelength]

11 hours ago, Fokus said:

But even if they did so, i.e. taking a 48kHz master, upsampling it to 96kHz, and then folding it into an MQA file, it would not do anything about the original 48k ADC ringing. This ringing cannot be removed, because this would mean cutting it out with a shallow filter starting far below 20kHz, and losing the music's treble in the process. Only the original pre-ringing can be converted into post-ringing, by means of a minimum phase filter cutting slightly below 24kHz (traditional Meridian CD player approach) or by manipulating phase above 20kHz (MQA's funny patent). Neither of these approaches require upsampling, they work perfectly fine in a 48kHz space.

 

Feel free to correct me if I am in error.  And to simplify discussion, I will stick to the 48 kHz family -- but the same should apply to the 44.1 kHz family.

 

A 48 kHz recording upsampled to 96 kHz via a minimum phase apodizing filter will put a null at 24 kHz Nyquist to notch out that ADC or downsampling digital filter ringing, replaced by post ringing at 48 kHz Nyquist.  In other words, the purported advantage would be that any pre or post ringing energy at 24 kHz Nyquist would be removed and shifted up an octave to post ringing at 48 kHz Nyquist.  I believe this was the rationale behind Dolby TrueHD with Advanced 96k Upsampling.

 

Regardless, I am not asserting that MQA is doing the above with 44.1/48 kHz masters.  We just do not know yet.  But the process described does have precedence as a Meridian kind of thing to do.

 

AJ

[crenca]

10 minutes ago, WiWavelength said:

 

 

Regardless, I am not asserting that MQA is doing the above with 44.1/48 kHz masters.  We just do not know yet.  But the process described does have precedence as a Meridian kind of thing to do.

 

AJ

 

The axiom "past behavior is the best predictor of future behavior" generally holds.

[Kal Rubinson]

1 hour ago, crenca said:

 

The axiom "past behavior is the best predictor of future behavior" generally holds.

Except in disclaimers.

[tmtomh]

4 hours ago, T.S. Gnu said:

Mister Stuart compared himself to Copernicus a while ago (Last para of article: http://www.theabsolutesound.com/articles/meridians-master-quality-authenticated-the-interview/). Sadly his following comment ("I guess I’m luckier, because the worst we’ll get is the wrath of audiophiles and scientists, not excommunication.") fearing excommunication further indicates fluidity with facts; Copernicus wasn't, and couldn't have been, excommunicated because his work was published after his death.

 

Having read this post, if I may be so bold, I would suggest you walk down the beach and think, "Now I know what Martin Luther felt." After all, this is addressing indulgences in a way. One could also say you could guess you will be luckier, because the worst you’ll get is the wrath of audiophiles and non-scientists, not excommunication. And you might be right because he, on the other hand, was excommunicated.

 

Irrespective of how this shakes out, history will view favourably the fact that issues were allowed to be discussed on this site free of dogma and preconception with intelligence not viewed as some hideous affliction. 

 

As to the question of anonymity that Mister Atkinson, Mister Stuart and their ilk bring up, it is perhaps respectfully fitting to quote a true follower in the steps of Copernicus:

"In questions of science, the authority of a thousand is not worth the humble reasoning of an individual." Galileo

 

Thanks for the link to that TAS interview with Stuart.

 

What knocks me out is that he's extolling the use of undersampling (via Nyquist Shannon) and using that notion to dismiss pretty much the entire audio/audiophile community as old-fashioned and ignorant (like flat-earthers compared to Copernicus).

 

To the best of my knowledge, undersampling makes sense only when the range of frequencies you need to sample is significantly narrower than the range of frequencies between DC (zero Hz) and the upper frequency you need to capture.

 

For example, a common cell phone frequency band is 1900MHz (not kHz), with a 100MHz bandwidth, meaning the phones operate from 1850MHz to 1950MHz. By using simple Nyquist theory, to digitize those waves, you'd have to sample them at 3900MHz, which is 2x the max frequency of 1950MHz.

 

Undersampling theory says it's a waste of data space and energy to use such a high sample rate, because the frequency band from zero Hz to 1850MHz contains no info, and so all the sampling of those frequencies is wasted. Instead, you can undersample and use the aliased frequencies to reconstruct the original signal, because while the aliased frequencies will be wrong, you will know exactly by how much they are wrong and you can use math to reconstruct the signals.

 

But in audio, the range is 20Hz to 20kHz. The only "wasted: sampling occurs between zero Hz and 20Hz, which is virtually nothing.

 

Now, it is true (as far as I know) that MQA uses undersampling theory to encode, enfold, and reconstruct some of the ultrasonics in MQA files. But as @mansr explained somewhere in these forums about a year ago, the result of doing this via MQA's chosen filters is that the price you pay for the reconstruction of ultrasonics is aliasing in the audible band. It's just silly.

[mansr]

20 minutes ago, tmtomh said:

To the best of my knowledge, undersampling makes sense only when the range of frequencies you need to sample is significantly narrower than the range of frequencies between DC (zero Hz) and the upper frequency you need to capture.

 

For example, a common cell phone frequency band is 1900MHz (not kHz), with a 100MHz bandwidth, meaning the phones operate from 1850MHz to 1950MHz. By using simple Nyquist theory, to digitize those waves, you'd have to sample them at 3900MHz, which is 2x the max frequency of 1950MHz.

 

Undersampling theory says it's a waste of data space and energy to use such a high sample rate, because the frequency band from zero Hz to 1850MHz contains no info, and so all the sampling of those frequencies is wasted. Instead, you can undersample and use the aliased frequencies to reconstruct the original signal, because while the aliased frequencies will be wrong, you will know exactly by how much they are wrong and you can use math to reconstruct the signals.

Right. The only restriction is that no multiple of half the sampling frequency may fall in the band of interest as these frequencies are impossible to capture unambiguously. If this is observed, reconstruction is as simple as applying a bandpass filter. As a special case, for sampling a modulated radio signal, it is ok for the carried frequency to be such a multiple since we only care about the deviations anyway. Needless to say, none of this is relevant for audio.

[Don Hills]

One thing I've been wondering about is the way the "folding"is done. Assuming 24/96 input, they split it into 0-24 and 24-48 kHz bands.

Do they then undersample the 24-48 kHz band to 0-24 kHz before compressing and encoding to 8 bits, then reverse on decode? If so, it would explain BS's assertion that they undersample.

[tmtomh]

4 hours ago, mansr said:

Right. The only restriction is that no multiple of half the sampling frequency may fall in the band of interest as these frequencies are impossible to capture unambiguously. If this is observed, reconstruction is as simple as applying a bandpass filter. As a special case, for sampling a modulated radio signal, it is ok for the carried frequency to be such a multiple since we only care about the deviations anyway. Needless to say, none of this is relevant for audio.

 

Thanks for the confirmation and further explanation!

 

I've bolded the last part of your comment, because in the TAS interview Stuart precisely makes the claim that this is relevant for audio, and that he's bringing the Good News to the us Philistines of the audiophile world. 

[FredericV]

9 hours ago, tmtomh said:

For example, a common cell phone frequency band is 1900MHz (not kHz), with a 100MHz bandwidth, meaning the phones operate from 1850MHz to 1950MHz. By using simple Nyquist theory, to digitize those waves, you'd have to sample them at 3900MHz, which is 2x the max frequency of 1950MHz.

 

In my realtek based SDR kit, it does not work this way from a logical standpoint.

My RTL sdr dongle has a max bandwidth of 3.2 Mhz. Dongles with more bandwidth (like 5 Mhz and 8 Mhz) also exists, but costs a lot more.

Suppose I want to capture the FM band and monitor anything between 100 and 102 Mhz. I specify 101 Mhz as the tuning frequency, with a bandwidth of at least 2 Mhz.

 

If I want to monitor a bigger part of the FM band (let's say 100-108 Mhz) that does not fit into the bandwidth of my dongle, my dongle will frequency hop, therefore missing at least 50% of the data.

My dongle is not sampling at 216 Mhz rate and exposing all this data over USB.
 

[Fokus]

6 hours ago, Don Hills said:

Do they then undersample the 24-48 kHz band to 0-24 kHz before compressing and encoding to 8 bits,

 

Yes.

 

[T.S. Gnu]

11 hours ago, Kal Rubinson said:

Except in disclaimers.

A pithily astute observation, sir.

[Fokus]

12 hours ago, WiWavelength said:

A 48 kHz recording upsampled to 96 kHz via a minimum phase apodizing filter will put a null at 24 kHz Nyquist to notch out that ADC or downsampling digital filter ringing, replaced by post ringing at 48 kHz Nyquist.

 

No.

 

If it is apodising in the Meridian sense, and oversampling, then yes, it will put a null at 24kHz (by means of starting to cut earlier than 24kHz, for the sake of argument say 20kHz), with all original ringing suppressed, and new pre-ringing at 20kHz. Not at 48kHz! For clarity, the filter I describe here is a steep minimum phase with a transition frequency slightly below the original Fs/2. Like this http://www.milleraudioresearch.com/download2008/reports/jun08/meridian_808_2cd.html (you'll need to register to get access).

But one does not even need to oversample to obtain this result: a simple minimum phase lowpass at 20kHz, still in 48k space, would do the same, and this pretty much regardless of the filtering strategy of the DAC used for replay.

 

Another possibility, although far-fetched, would be to oversample with an MQA-style leaky filter, PLUS a minimum phase notch filter at 24kHz. The output of such would show post-ringing at bandpass edges of the notch (ie.g. 22kHz and 26kHz), a hole at 24kHz, and a spray of images 26-48kHz.

 

Curiously, this is what we see when playing Lemonade on an MQA DAC. However, the normal CD-derived version of Lemonade also has this hole between 20 and 22kHz, so what appears to be a notch in the analogue output, is not a notch (but rather a low-pass with its mirror image), and has nothing to do with MQA.

 

I can't show figures etc: as I mentioned before, I no longer have Tidal, nor base-rate raw MQA files.

 

I am also not much interested in MQA anymore.

 

 

[adamdea]

On 16/03/2018 at 7:47 AM, Fokus said:

 

Not linear phase. Presumably an additional all-pass network that reduces the non-linear phase component in its response somewhat. I'll see if I can find that old group delay plot.

 

 

Edit: got it.

 

Look in this document at Figure 3 and the text below it.

 

http://www.audio-focus.com/Townsend/pdf/Why_supertweeters.pdf

 

 

(Apparently with thanks to Peter Baxandall...)

Thanks for this- am largely incommunicado this week on St. Bernard pass, but will have a look on my return 

[Pete-FIN]

On 12.3.2018 at 3:17 PM, Doug Schneider said:

Since the 1990s, Stereophile has been sold a number of times. Each new publishing company instills a new set of rules.

 

Breaking news, the ownership of Stereophile has changed.

 

The news story is here:

https://www.stereophile.com/content/avtech-media-ltd-uk-acquires-home-tech-network-ten-publishing-media

 

AVTech Media Ltd (UK) has purchased the Home Tech Network...

 

The Home Tech Network's six brands including Stereophile, Sound & Vision, Shutterbug, AnalogPlanet, Audiostream, and Innerfidelity...

 

It will be interesting to follow if there is journalistic changes in Stereophile.

[The Computer Audiophile]

4 minutes ago, Pete-FIN said:

 

Breaking news, the ownership of Stereophile has changed.

 

The news story is here:

https://www.stereophile.com/content/avtech-media-ltd-uk-acquires-home-tech-network-ten-publishing-media

 

AVTech Media Ltd (UK) has purchased the Home Tech Network...

 

The Home Tech Network's six brands including Stereophile, Sound & Vision, Shutterbug, AnalogPlanet, Audiostream, and Innerfidelity...

 

It will be interesting to follow if there is journalistic changes in Stereophile.

I can just see the war on pseudonyms beginning now :~) 

[botrytis]

2 hours ago, The Computer Audiophile said:

I can just see the war on pseudonyms beginning now :~) 

 

I have used this moniker since 1996  

 

I find nothing wrong with it. Some of the most read authors use them.

[Rt66indierock]

3 hours ago, The Computer Audiophile said:

I can just see the war on pseudonyms beginning now :~) 

 

Or all the MQA press in TEN was just to increase numbers so TEN could sell off the Home Tech Network.

[realhifi]

21 hours ago, botrytis said:

 

I have used this moniker since 1996  

 

I find nothing wrong with it. Some of the most read authors use them.

Fiction writers do.