John Atkinson: Yes, MQA IS Elegant...

[John_Atkinson]

2 hours ago, Jud said:

The reason the Ayre filter doesn't ring is because it isn't very steep, so it may let through some frequencies that create aliasing, imaging, and higher THD numbers.  (Not sure I'm remembering correctly, but Ayre DACs may at least at one time have had different "Listen" and "Measure" filters.)

 

If you read my article (which isn't specifically about MQA but about A/D conversion in general), you should note that the filter I mention that is free from ringing is the Ayre QA-9's antialiasing filter at 2Fs and 4Fs rates in the its "Listen" setting. Yes, the QA-9's Listen filter allows for image energy to fold back below Nyquist but both Charley Hansen and Bob Stuart have pointed put that at 2Fs and 4Fs rates, there is very little musical energy to be aliased.

 

Ayre's reconstruction filters in its D/A converters are minimum-phase types that ring, either for a short time (Listen) or longer (Measure). The Ayre D/A filter that doesn't ring is an experimental type that Charley Hansen sent me during the discussions we had on this subject before he passed away and that I refer to in the article; it is not available to owners of Ayre D/A processors. So as very few commercial recordings have been made with the Ayre QA-9's Listen filter, it would appear that if removing so-called "temporal bur" is indeed something that improves sound quality for the reasons I explain in the article,  the MQA process is one of the few commercially available end-to end solutions that would do that. If...

 

John Atkinson

Editor, Stereophile

 

[John_Atkinson]

2 minutes ago, crenca said:

What say you internet forum members, you who are "nasty", ignorant, and troublesome according trade publications such as Stereophile?

 

For the record, I have never referred to people who post to forums like this as "'nasty', ignorant, and troublesome." However, I do think, judging from many of the comments in this thread, that people often don't actually read what I wrote before commenting. So it goes.

 

John Atkinson

Editor, Stereophile

[John_Atkinson]

13 minutes ago, Jud said:

Thanks John. 

You're welcome.

 

Quote

I'm confused about the mention of a non-ringing filter as both something available in the QA-9, and something not available to Ayre owners, and would appreciate if you could clear that up.

 

The QA-9 is a now-discontinued A/D converter that used a moving-average filter (12 samples at a time IIRC) at its 2Fs and 4FS rates. My article shows that while the QA-9's Measure anti-aliasing filter is a (short) minimum-phase type, the Listen filter produces a impulse response, examined in the digital domain, with no ringing before or after. The Ayre D/A converters don't have such a filter; while Charley Hansen and his team created a complementary reconstruction filter to that in the QA-9, this is not available to owners of Ayre DACs. Charley sent this experimental filter to me to test; his doing so was the genesis of my article.

 

John Atkinson

Editor, Stereophile

 

[John_Atkinson]

4 minutes ago, Brinkman Ship said:

Perhaps he was referring to this post, by "jeffhenning"

 

"...in fact, usually, very little knowledge is what is exhibited by people who are dilettante A-holes with strong opinions about audio that disagree with you, John.

 

You do understand that I am not "jeffhenning"?

 

John Atkinson

Editor, Stereophile

[John_Atkinson]

1 hour ago, Miska said:

In latest Stereophile J. Atkinson was once again going for the age old fallacy of looking only one aspect of the the filters (time domain) without putting the other aspect (frequency domain) side by side with it.

 

We have already examined the frequency-domain performance of sharp rolloff- filters and "leaky" ones like MQA's upsampling filter. As I wrote earlier in this thread, it would be helpful if people actually read what we have written instead of firing from the hip.

 

John Atkinson

Editor, Stereophile

 

[John_Atkinson]

7 minutes ago, crenca said:

John Atkinson in that thread - it's August 2018 folks! - is STILL asserting that MQA is "the only commercially available end-to-end solution". 

 

Please note that time-domain performance was the context for this posting to the Audio Asylum, not DRM, not the possibility of aliasing, not the file size, not the lossy vs lossless argument. In that context, I wrote "MQA, _if_ it operates as describes and as I investigated in my article, is the only commercially available end-to end solution. (Unless you consider very high-bitrate DSD implemented with complementary first-order low-pass filters.)"

 

As you appear to be arguing with that assertion, what other combinations of commercially available A/D converter and D/A conversion, other than MQA, Ayre's experimental filters, or, possibly, high bit-rate DSD, give you perfect behavior in the time domain from analog original signal to the analog reconstruction of that signal?

 

John Atkinson

Editor, Stereophile

[John_Atkinson]

3 minutes ago, mansr said:

Why would you need matched A/D and D/A converters? That isn't how sampling works.

 

This is explained in the article of mine on stereophile.com that initiated this thread. I acknowledge that some might not want to read that article and by doing so gift us page views, but so it goes.

 

John Atkinson

Editor, Stereophile

[John_Atkinson]

18 minutes ago, mansr said:

Nobody is saying that filters don't "ring" when applied to impossible signals.

 

You can see from the article of mine that triggered this thread an example where a perfectly legal, band-limited impulse nevertheless excites the DAC reconstruction filter's sinc-function ringing.

 

John Atkinson

Editor, Stereophile

 

[John_Atkinson]

6 minutes ago, mansr said:

  36 minutes ago, John_Atkinson said:

band-limited impulse

 

Ain't no such thing. Please use standard maths/engineering terminology if you want to be taken seriously.

 

Okay, a very short unidirectional waveform, sampled at 44.1kHz, that has no spectral content above 22.05kHz.

 

John Atkinson

Editor, Stereophile

[John_Atkinson]

2 hours ago, adamdea said:

I think I read your article and can’t recall a band limited impulse. Can you refer to the precise text and/or figure number. 

 

Fig.12 at https://www.stereophile.com/content/zen-art-ad-conversion-page-2

 

John Atkinson

Editor, Stereophile

 

[John_Atkinson]

5 hours ago, adamdea said:

Sorry - but that seems to me to be the "impulse response" of a dac fed *something*.

 

Fig.12 in my article plots the sample values in the digital domain. No DAC involved.

 

Quote

The something seems to be a non band limited impulse fed to a QA at 96khz and then sample rate converted to 44.1.

 

To create those digital-domain data, I digitized at 96kHz a unidirectional, shaped analog pulse with an approximate bandwidth of 60kHz with the Ayre QA9 A/D converter with its "Listen" antialiasing filter. I then sample-rate-converted those data to 44.1kHz. This is described in the article.

 

Quote

Why are you calling this a perfectly legal band limited impulse" ?

 

Because there is no spectral content above the new Nyquist frequency of 22.05kHz, due to the SRC's high-order low-pass filter. (Actually, spectral content above 22.05kHz analyzed in the digital domain after resampling to 96kHz, lies at approximately -127dB ref. the peak pulse level.) It is thus a "legal" 44.1kHz signal.

 

John Atkinson

Editor, Stereophile

 

[John_Atkinson]

22 hours ago, crenca said:

have we not come to the conclusion that the impulse that JA used to illicit "ringing" in his article is in fact an "illegal" frequency outside of the 20-20 band limit? 

 

As I have said before, spectral analysis shows that the "band-limited impulse" I used has no content above 22.05kHz. However, as I showed in the article, it does have sinc-function ringing present at 22.05kHz.The inference to be drawn is that every musical transient in a CD master will be accompanied by sinc-function ringing at Nyquist, either from the original A/D converter's anti-aliasing filter (if the recording was made at 44.1kHz), or from the sample-rate converter's low-pass filter used to create the master from 2Fs or 4Fs files. It seems incontrovertible, therefore that that ringing will excite the playback DAC's reconstruction filter, which will impose its own ringing on musical transients.

Read more at https://www.stereophile.com/content/zen-art-ad-conversion

 

John Atkinson

Editor, Stereophile

 

[John_Atkinson]

3 hours ago, Fokus said:

You used Bias Peak for the sample rate conversion, i.e. anti-alias filtering followed with downsampling. If you did spectral analysis on the result you could only have done this after the downsampling, which is wrong.

 

As explained earlier in this thread, I resampled the 44.1kHz file to 96kHz, in order to examine the content above 22.05kHz in the digital domain and compare that result with the content of the file before downsampling.

 

John Atkinson

Editor, Stereophile

[John_Atkinson]

23 minutes ago, psjug said:

It would be incontrovertible if you show some hi-res captures of 16/44 DAC output showing the musical transients with all the ringing.

 

This was shown in the article.

 

John Atkinson

Editor, Stereophile

 

[John_Atkinson]

4 minutes ago, mansr said:

That makes no sense. A 44.1 kHz file has, by definition, no content above 22.05 kHz.

 

Please read the thread. I was responding to the assertion made by several posters, that the ringing of the DAC's reconstruction filter was due to the down-sampled file having spectral content above 22.05kHz. It didn't.

 

John Atkinson

Editor, Stereophile

[John_Atkinson]

23 minutes ago, Jud said:

The fact that the Fast Roll-off filter "substituted its own...ringing" pretty well shows that there was content *at* the cutoff frequency, at least.

 

That's correct. This is examined in the article.

 

John Atkinson

Editor, Stereophile

 

[John_Atkinson]

8 hours ago, wdw said:

Like JA, I can only imagine there must be some share allocation implied or some honey pot mentioned if MQA succeeds...Must assume that JA and Harley are simply collaborators following some corporate game plan....JA, is this your chosen legacy?  .....a YES man with a few bucks in your pocket?  

 

This accusation has been made before on this website. For the record, I do not benefit personally in any way whatsoever if MQA succeeds nor do I suffer in any way if it fails.

 

I am disappointed that Chris Connaker allows such false accusations to be posted to this site.

 

John Atkinson

Editor, Stereophile

[John_Atkinson]

On 9/4/2018 at 2:52 PM, vl said:

The recent article by JA using various ADCs, DACs and SRC software further confuses the issue of what a good digital recording should be from a time and frequency domain stand points, by talking about filter ringing caused by improperly band limited signals entering the digital recording/reproduction chain.

 

It saddens me that so much of this thread has degenerated into personal attacks, from people who have not read what I have written or, if they have done so, have not understood it, as in the case of the post which I am responding. Too many posters have a greater confidence in their opinions than they do actual knowledge, driven by what appears to be antagonism toward those of us who earn our livings by what we publish and write.

 

When I was studying 45 years ago to get my post-graduate qualification as a high-school science teacher, I read a lot of the works of philosopher Karl Popper. I was recently reminded of something he wrote in "The Open Society and Its Enemies": "A healthy society means a competition for ideas . . . and critical thinking that considers the facts, not who is presenting them." (my italics)

 

So putting aside the fact it was I who wrote the article that triggered this thread, consider the facts:

 

The experimental evidence I presented is incontrovertible. That unless the user of an A/D converter is prepared to accept the possibility of some aliased image energy in order to use an antialiasing filter that preserves the time-domain behavior of the original analog signal, the resultant digital data will have sinc-function content at the Nyquist frequency accompanying every musical transient.

 

If the original data were captured at 2Fs and or 4FS rates, then the sample-rate converter used to prepare a CD master will introduce ringing at the new Nyquist frequency of 22.05kHz with every musical transient.

 

Decoding these correctly band-limited digital data with a conventional sinc-function reconstruction filter will replace this ringing with its own, again at Nyquist, with every transient. A slow-rolloff reconstruction filter will not ring but will preserve the Nyquist-frequency ringing in the original data.

 

If a specific type of slow-rolloff antialiasing filter in the A/D converter is combined with a reconstruction filter in the D/A converter that behaves in a similar manner, you will have an analog-digital-data storage/transmission-digital-analog chain that will have an impulse response and top-octave rolloff equivalent to that of a small distance of air. As I wrote in my article, this was the stated goal of both Bob Stuart and the late Charley Hansen; I see no disrespect to the latter in pointing that out, especially as I instanced Charley's antipathy to MQA in the article.

 

In the context of Popper's comment, what should be debated are the following questions:

 

Does the MQA analog-analog chain behave in the same manner as the Charley Hansen's "Listen" anti-aliasing filter in the Ayre QA-9 and his experimental reconstruction filter for the Ayre QX-5 Twenty? You will note that I used the word "if" in my article. Without access to an MQA-equipped A/D converter, that must be speculation on my part. (I have asked to try Mytek's MQA ADC, but I would have to sign a non-disclosure agreement that makes my using it moot.)

 

Is the compromise in the frequency domain associated with using time-domain-perfect converters acceptable with real musical signals? Or is the possibility of image energy being aliased into the audioband too great? I have heard arguments on both sides of this question. I suspect the answer is that it depends on the type of music.

 

Does ringing at 22.05kHz even matter when it comes to sound quality? Again, I have heard arguments on both sides of this question, from people I respect.

 

And that, I would hope, is my final word on this matter.

 

John Atkinson

Editor, Stereophile

 

 

[John_Atkinson]

3 minutes ago, mansr said:

It is difficult to understand a text when its author, apparently, doesn't understand the subject matter.

 

So there we have it. No discussion of the points I raised, just another personal attack.

 

So be it.

 

John Atkinson

Editor, Stereophile

[John_Atkinson]

4 minutes ago, FredericV said:

30 minutes ago, John_Atkinson said:

I have asked to try Mytek's MQA ADC, but I would have to sign a non-disclosure agreement that makes my using it moot.

Why is there still no MQA enabled ADC?

 

I thought it clear from my post that Mytek has such an ADC. Some recording and mastering engineers in the NY area have been beta-testing it.

 

John Atkinson

Editor, Stereophile

 

[John_Atkinson]

Just now, FredericV said:

I repeat my question, which you are avoiding: why is there only one ADC with MQA (in beta)?.

 

Your original question was "Why is there still no MQA enabled ADC?" To be clear, this isn't the same question, so you are hardly repeating it. But to answer this second question, I have no idea. Nor do I have any idea why you think I should know.

 

John Atkinson

Editor, Stereophile

[John_Atkinson]

30 minutes ago, adamdea said:

I can’t see how this could be described as  incontrovertible- it seems to me doesn’t even get off the ground because you did not start with a musical transient, let alone one captured with a real microphone.

 

That is correct. I used an artificially generated, non-musical test signal with the necessary properties to investigate the subject in a repeatable and diagnostic manner. The use of such signals to investigate the behavior of audio components and infer the results of that behavior with music is routine. You can find myriad examples in the review archive at www.stereophile.com.

 

John Atkinson

Editor, Stereophile

 

[John_Atkinson]

2 minutes ago, vl said:

Could you enlighten us how does your artificially generated test signal relate to a music signal or a musical listening experience?

In the context of testing audio components, this is an enormous subject. All I can suggest is that you read the tutorial articles in the free on-line archives at the Stereophile website.

 

John Atkinson

Editor, Stereophile