Stereophile Series on MQA Technology

[NOMBEDES]

17 hours ago, barrows said:

A really good phono stage is much harder to achieve and build than a line level preamp.  A phono stage is probably the most difficult analog component to get really fantastic performance out of because the incoming signal level is so low, especially when considering low output MC cartridges.

When i said SOTA, BTW, i was referring to performance, not cosmetics

 

@barrows.  You are 100% correct, I think most of us know that a Phono stage is a design challenge.   However, I was responding to a question relating to overall cost of high end components.  Indeed, cosmetics represent a good portion of cost at the higher end.

 

[GUTB]

35 minutes 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.

 

It is also true that, unless the original signal contained high-level energy at the filter's cut-off point, the ringing as displayed does not appear in the sampled music signal.

 

Impulse response testing is done in digital audio because it is the fastest and simplest method for revealing the nature of the underlying digital filter(s). That is all.

 

No, that is not all ...

 

Impulse response testing is done in consumer digital audio because it is a handy tool for instilling fear and uncertainty in the minds of a techno-illiterate audience.

 

 

 

So what you’re saying is that impulse response testing as commonly performed in reviews is meaningless and only exists to film-flam consumers?

[mansr]

Just now, GUTB said:

So what you’re saying is that impulse response testing as commonly performed in reviews is meaningless and only exists to film-flam consumers?

The conclusions presented are often incorrect or misleading, even if the test as such was performed correctly. Case in point, Jim Austin's MQA piece.

[barrows]

2 hours ago, semente said:

 

Interesting, recently Charles Hansen was underlining the importance of the analogue stage, saying that it accounted more to the overall sound than any other aspect.

 

 

And yet that QX-5 isn't exactly a stellar performer:

 

Ayre QX-5 Twenty, DAC mode, spectrum of 50Hz sinewave,

DC–1kHz, at 0dBFS into 100k ohms

(left channel blue, right red; linear frequency scale)

 

Ayre QX-5 Twenty, Music filter, DAC mode, HF intermodulation spectrum,

DC–30kHz, 19+20kHz at 0dBFS into 600 ohms, 44.1kHz data

(left channel blue, right red; linear frequency scale)

 

In the case of the QX-5 the analogue output stage accounts for a lot of the sound as it's hardly "transparent".

If you do not understand the technical reasons why those are there, please do not point to the QX-5's analog stage.  All of the artifacts you see there are due to the leaky filter, and have nothing to do with analog stage performance.  The fact that those are there are subjective choices made by Ayre in the development of their filter.  Those artifacts are there as a choice, on purpose.

[mansr]

3 minutes ago, barrows said:

If you do not understand the technical reasons why those are there, please do not point to the QX-5's analog stage.  All of the artifacts you see there are due to the leaky filter, and have nothing to do with analog stage performance.

Those graphs show large amounts of non-linear distortion. It is impossible for a FIR or IIR anti-imaging filter to cause this, no matter how leaky.

[psjug]

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?

 

[barrows]

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.

 

It is also true that, unless the original signal contained high-level energy at the filter's cut-off point, the ringing as displayed does not appear in the sampled music signal.

 

Impulse response testing is done in digital audio because it is the fastest and simplest method for revealing the nature of the underlying digital filter(s). That is all.

 

No, that is not all ...

 

Impulse response testing is done in consumer digital audio because it is a handy tool for instilling fear and uncertainty in the minds of a techno-illiterate audience.

 

 

Yes, and also interesting is that the MQA filters produce clipping if subject to hi level signals any high frequencies, as pointed out by J. Atkinson.  JA brushed this off by saying: thankfully music rarely has that much energy at those frequencies.  Still I would rather not have a filter which could potentially produce clipping, as digital overs really sound bad.

[barrows]

1 hour ago, NOMBEDES said:

 

@barrows.  You are 100% correct, I think most of us know that a Phono stage is a design challenge.   However, I was responding to a question relating to overall cost of high end components.  Indeed, cosmetics represent a good portion of cost at the higher end.

 

Agreed.  When we get to very high price products, say the 5 figures range, cosmetics are going to represent a significant portion of the cost, this is due to customer demand, and not a "fault" of the manufacturer.  But things you mentioned like ceramic PCBs and polishing connections are not cosmetic, those are specifically done to increase actual performance.  Alternate PCB materials reduce capacitance/parasitics, and polishing connections reduces resistance of those connections.

[barrows]

@mansr

 

Please take a look here:

 

https://www.stereophile.com/content/ayre-acoustics-qx-5-twenty-da-processor-measurements

 

Compare figs 10 and 11.  Filter choice is producing the artifacts.

 

If you are referring to the distortion profile seen in fig 9, yes, the THD is a little high compared to some DACs.  But again this is a conscious choice on the part of Ayre's engineers as they use no loop negative feedback on purpose, because they feel it sounds better, despite the slightly higher distortion profile.  

 

I think people need to relax a bit about some of this though.  Distortion at even -90 dBFS is very low in terms of audibility in the real world.  For folks at home, get a copy of Stereophiles test CD-2 and play the low level 1 kHZ tone test.  This gives you a 1 kHz tone at -90 dB.  Play it with your volume at your normal critical listening level.  You might be surprised how low in level, in room, even -90 dB is.  And, we must remember this harmonic distortion, and not an anharmonic artifact.  Harmonic distortion is much less bothersome to the human ear/brain than anharmonic artifacts-hence Ayre's subjective choice to use no feedback for what they feel is better sound quality.

 

For someone to suggest that the Ayre analog stage is poorly designed completely misses the point.  Ayre's analog stage is designed to be this way on purpose, it is doing exactly what they want.  I am pretty familiar with the Ayre guys, and they have a very competent engineering staff.  They could just as easily designed a DAC with vanishingly low THD, they do it this way for a reason.

 

[mansr]

44 minutes ago, barrows said:

@mansr

 

Please take a look here:

 

https://www.stereophile.com/content/ayre-acoustics-qx-5-twenty-da-processor-measurements

 

Compare figs 10 and 11.  Filter choice is producing the artifacts.

The filter setting might be also switching something in the analogue section. The digital filters we are discussing here are mathematically unable to produce those effects.

 

44 minutes ago, barrows said:

For someone to suggest that the Ayre analog stage is poorly designed completely misses the point.  Ayre's analog stage is designed to be this way on purpose, it is doing exactly what they want.  I am pretty familiar with the Ayre guys, and they have a very competent engineering staff.  They could just as easily designed a DAC with vanishingly low THD, they do it this way for a reason.

A purposely poor design is still poor.

[barrows]

28 minutes ago, mansr said:

The filter setting might be also switching something in the analogue section. The digital filters we are discussing here are mathematically unable to produce those effects.

That is not correct.  As far as the maths go, I do not know what to say, but the two results shown here are just the result of the two different filters, there are no changes taking place in the analog section.

[barrows]

30 minutes ago, mansr said:

A purposely poor design is still poor.

This, is a matter of opinion and nothing more.  And your opinion on analog circuit design would carry a bit more weight if you ran a company producing some really good sounding DACs.

No one is being forced to purchase the Ayre QX-5, but people seem to be liking it a quite a lot, so it would appear to me that Are has done OK with their design choices.

[semente]

1 hour ago, barrows said:

If you do not understand the technical reasons why those are there, please do not point to the QX-5's analog stage.  All of the artifacts you see there are due to the leaky filter, and have nothing to do with analog stage performance.  The fact that those are there are subjective choices made by Ayre in the development of their filter.  Those artifacts are there as a choice, on purpose.

 

Could make your point more clearly?

I understand that the leaky "Music" filter measures very badly but the "measure" filter doesn't perform much better:

 

Ayre QX-5 Twenty, Measure filter, DAC mode, HF intermodulation spectrum,

DC–30kHz, 19+20kHz at 0dBFS into 600 ohms, 44.1kHz data

(left channel blue, right red; linear frequency scale)

[barrows]

@semente, the point is that the filter response is on purpose.  Ayre could make those filter responses look any way they want to (within the realm of the possible).  They chose the responses they did to achieve the sound quality they were looking for.  The customer/listener is free to like it, or not, as they see fit, but Ayre makes it this way on purpose, because they want it to be this way for sound quality reasons.

[GUTB]

Measuring tools are insufficient for evaluating subjective sound quality -- which is why real high-end manufacturers design their products via ear. Ayre is a very well-regarded company with a master of the art behind it (sadly passed away, taking a great talent from us). I don't believe there is a single negative thing said about Ayre sound, anywhere, regardless of taste.

[semente]

1 minute ago, GUTB said:

Measuring tools are insufficient for evaluating subjective sound quality -- which is why real high-end manufacturers design their products via ear. Ayre is a very well-regarded company with a master of the art behind it (sadly passed away, taking a great talent from us). I don't believe there is a single negative thing said about Ayre sound, anywhere, regardless of taste.

You can say that the measurements of the QX-5 are mediocre. And measurements define the degree of accuracy for specific parameters.

[mansr]

44 minutes ago, semente said:

Could make your point more clearly?

I understand that the leaky "Music" filter measures very badly but the "measure" filter doesn't perform much better:

 

Ayre QX-5 Twenty, Measure filter, DAC mode, HF intermodulation spectrum,

DC–30kHz, 19+20kHz at 0dBFS into 600 ohms, 44.1kHz data

(left channel blue, right red; linear frequency scale)

I suspect what's going on here is that analogue circuitry causes the distortion seen with the "measure" filter. With the "music" filter, the added high-frequency images cause the additional distortion products observed with that setting.

[mansr]

1 hour ago, barrows said:

That is not correct.  As far as the maths go, I do not know what to say, but the two results shown here are just the result of the two different filters, there are no changes taking place in the analog section.

I just told you what the maths says.

[Miska]

47 minutes ago, mansr said:

I suspect what's going on here is that analogue circuitry causes the distortion seen with the "measure" filter. With the "music" filter, the added high-frequency images cause the additional distortion products observed with that setting.

 

Yeah, there's some amount of distortion from the analog stage, due to the no-feedback nature of it.

 

[Miska]

3 hours ago, barrows said:

Yes, and also interesting is that the MQA filters produce clipping if subject to hi level signals any high frequencies, as pointed out by J. Atkinson.  JA brushed this off by saying: thankfully music rarely has that much energy at those frequencies.  Still I would rather not have a filter which could potentially produce clipping, as digital overs really sound bad.

 

Classical music... But someone needs to put some heavymetal or digitally produced EDM through it for some fun. Or just over compressed modern pop with lot of digital clipping. Not unusual to have transients going flat-out to 20 kHz.

 

[Miska]

3 hours ago, mansr said:

Those graphs show large amounts of non-linear distortion. It is impossible for a FIR or IIR anti-imaging filter to cause this, no matter how leaky.

 

It is one of the potential side-effects of leaky filters, and also insufficient oversampling ratios. Generated in the analog stages. Both produce lot of correlated ultrasonic tones mirrored around multiples of the sampling rate. Depending on analog stages, those may cause intermodulation products in the audio band. For example 1 kHz tone causes IMD product at 2 kHz due to the difference between negative and positive frequency around multiples of sampling rate. And harmonic distortion products from earlier stages can also cause intermodulation tones in the later stages, and intermodulation products from earlier stages can again have their own harmonic distortion products in the later stages...

[beetlemania]

3 hours ago, barrows said:

If you are referring to the distortion profile seen in fig 9, yes, the THD is a little high compared to some DACs.  But again this is a conscious choice on the part of Ayre's engineers as they use no loop negative feedback on purpose, because they feel it sounds better, despite the slightly higher distortion profile.  

 

/snip/

 

For someone to suggest that the Ayre analog stage is poorly designed completely misses the point.  Ayre's analog stage is designed to be this way on purpose, it is doing exactly what they want.  I am pretty familiar with the Ayre guys, and they have a very competent engineering staff.  They could just as easily designed a DAC with vanishingly low THD, they do it this way for a reason.

 

 

Charles Hansen, in his own words:

Quote

The fact that an integrated circuit has achieved a (best case) THD+noise level of 0.0003% is impressive, no doubt. But what does this really mean in the real world? It merely means that the designers have applied such a high level of feedback that nonlinearities, as measured with a static test signal (ie, one that does not mimic actual music), are minimized, along with achieving a respectably low level of noise.

 

Quote

But does this low level of measured distortion actually translate to improved sound quality when listening to music? The answer is a resounding "No!"

So, yes, designed that way on purpose.

 

But this is WAY off topic . . .

[mansr]

15 minutes ago, Miska said:

It is one of the potential side-effects of leaky filters, and also insufficient oversampling ratios. Generated in the analog stages. Both produce lot of correlated ultrasonic tones mirrored around multiples of the sampling rate. Depending on analog stages, those may cause intermodulation products in the audio band. For example 1 kHz tone causes IMD product at 2 kHz due to the difference between negative and positive frequency around multiples of sampling rate. And harmonic distortion products from earlier stages can also cause intermodulation tones in the later stages, and intermodulation products from earlier stages can again have their own harmonic distortion products in the later stages...

All true. What I meant was, non-linear distortion can't be a direct result of a linear filter. With an ideal analogue section, no digital filter (of the types used in oversampling DACs) selection could result in intermodulation or harmonic distortion.

[semente]

4 hours ago, barrows said:

For someone to suggest that the Ayre analog stage is poorly designed completely misses the point.  Ayre's analog stage is designed to be this way on purpose, it is doing exactly what they want.

 

Let me rephrase this more accurately (pun intended):

 

Ayre's analog stage is poorly designed to be this way on purpose, it is doing exactly what they want.

[semente]

2 hours ago, barrows said:

This, is a matter of opinion and nothing more.  And your opinion on analog circuit design would carry a bit more weight if you ran a company producing some really good sounding DACs..

 

The problem with your rationale is the "good sounding" part. Good sounding to whom? It's your opinion, not a universally accepted fact.