MQA technical analysis

[mansr]

It's graph time again. 2L-111 is a 352.8 kHz master with remarkably low high-frequency noise. Here's the spectrum of the original and the MQA reconstruction (decode + render):

 

 

According to my analysis of the renderer, this is the filter used by its 4x upsampling with this file:

 

 

It's a 24-tap minimum phase FIR filter. There is a notch centred at 88.2 kHz, which is clearly visible in the "rendered" music. Towards the high end of the spectrum, the filter again attenuates, and the shaped dither noise swamps whatever remains of the images there.

[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.

[adamdea]

It's graph time again. 2L-111 is a 352.8 kHz master with remarkably low high-frequency noise. Here's the spectrum of the original and the MQA reconstruction (decode + render):

 

[ATTACH=CONFIG]32642[/ATTACH]

 

More spuriae 50-100khz than there is program material over 20khz. Remind me what's wrong with 16/44 again?

[mmerrill99]

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.

Exactly correct. This is the kernel question in audio 'quality' evaluation - what is scale of importance assigned by auditory processing, to the various distortions/factors encountered in our audio playback chain.

[Ralf11]

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

 

True, unless....

 

unless "accuracy" is a multi-factorial concept and one can generate an indifference function (response surface) that, while worse in some ways is so much better in others, that it can be claimed to be....

 

more accurate.

[Don Hills]

... According to my analysis of the renderer, this is the filter used by its 4x upsampling with this file:

 

[ATTACH=CONFIG]32643[/ATTACH]

 

It's a 24-tap minimum phase FIR filter. There is a notch centred at 88.2 kHz, which is clearly visible in the "rendered" music. Towards the high end of the spectrum, the filter again attenuates, and the shaped dither noise swamps whatever remains of the images there.

That bears a remarkable resemblance to Jim Lesurf's suggestion of the required filter response.

MQA 192k / 96k There and back again.

[Miska]

May be there is especial initialization of the DAC is need?

 

It is USB Audio Class 2 compliant device.

 

Such behaviour of DAC with any playback software (in bit perfect mode, of course)?

 

I'm just using "aplay" on Linux. Doesn't get much simpler than that.

 

Possibly it is damaged DAC.

 

Yes, in a sense of buggy firmware. It is anyway latest available one, I checked right before doing the tests.

[Miska]

It's graph time again. 2L-111 is a 352.8 kHz master with remarkably low high-frequency noise. Here's the spectrum of the original and the MQA reconstruction (decode + render):

 

[ATTACH=CONFIG]32642[/ATTACH]

 

Nicely shows how they cut on high frequencies above 30 kHz (more like 25 kHz in this case) and then add bunch of artefacts in the higher ultrasonic range...

[mansr]

Nicely shows how they cut on high frequencies above 30 kHz (more like 25 kHz in this case) and then add bunch of artefacts in the higher ultrasonic range...

 

The artefacts here are mainly images from the upsampling and shaped dither. Neither has anything to do with the original signal.

[Ralf11]

do we care about 30 kHz and up freqs.?

 

if so, why?

 

seems like it is easy to filter to prevent noise injection...(?)

[audiventory]

do we care about 30 kHz and up freqs.?

 

if so, why?

 

seems like it is easy to filter to prevent noise injection...(?)

 

It is not so rare case.

 

The ultrasound harmonics may cause audible noise by intermodulations.

 

Of course, need ultrasound filter.

[Miska]

do we care about 30 kHz and up freqs.?

 

I do, that's what the hires is about. You shouldn't remove anything that is captured during recording and you should record everything the instruments generate. To fully reproduce instrument's sound, you cannot remove anything from it. That's why I have speakers and headphones that go to 50+ kHz and amplifiers that can cleanly reproduce 100+ kHz flat.

 

It is contradictory to talk about deblurring while simultaneously having low-pass filter that cuts on high frequencies, because that will precisely cause slowing down of the transient edges. Faster the transient, more high frequency components it will have.

There's life above 20 kilohertz! A survey of musical instrument spectra to 102.4 kHz

 

Now if MQA removes both LSB bits and cuts on high frequencies, it is removing pretty much all "hires" out of "hires". So it just becomes expensive way to create mangled "lores".

[Miska]

The ultrasound harmonics may cause audible noise by intermodulations.

 

Of course, need ultrasound filter.

 

What should be removed are the digital image frequencies and modulator noise, but those are at frequencies way over 150 kHz spreading to MHz range. What shouldn't be removed is real audio content below 150 kHz or so.

 

What MQA doesn't help at all, are those things above 150 kHz. Instead it generates digital images/aliasing under 150 kHz.

[audiventory]

What should be removed are the digital image frequencies and modulator noise, but those are at frequencies way over 150 kHz spreading to MHz range. What shouldn't be removed is real audio content below 150 kHz or so.

 

What MQA doesn't help at all, are those things above 150 kHz. Instead it generates digital images/aliasing under 150 kHz.

 

Do you don't agree that 30 and 33 kHz harmonics can cause 3 kHz (33 - 30) harmonic in audible spectrum by intermodulations?

[mansr]

Do you don't agree that 30 and 33 kHz harmonics can cause 3 kHz (33 - 30) harmonic in audible spectrum by intermodulations?

 

Yes, that can and does happen. That doesn't mean it's impossible to design equipment where it doesn't.

[audiventory]

Yes, that can and does happen. That doesn't mean it's impossible to design equipment where it doesn't.

 

If say exactly, impossibly create equipment that don't cause intermodulations. Because any active electronic device is nonlinear.

 

However, different equipment provide different level of intermodulations depending on form of input-output characteristic (level-gain curve).

[Miska]

Do you don't agree that 30 and 33 kHz harmonics can cause 3 kHz (33 - 30) harmonic in audible spectrum by intermodulations?

 

Yes, but only in shitty electronics not worth having. I'm much more concerned about for example 330 + 333 kHz or 1030 + 1033 kHz image harmonics.

 

For example when the digital filter outputs 352.8 kHz rate followed by zero-order-hold. When you play 1 kHz tone, the DAC will output both 351.8 and 353.8 kHz tones and thus intermodulation product of 2 kHz. And this is directly correlated with the input signal. This is further emphasized by the fact that at 350 kHz range the THD of analog sections will be higher, and thus also harmonic distortion products of these frequencies will cause also intermodulation products.

 

With music, the level of 1 kHz tones is also generally much higher than 30 and 33 kHz harmonics.

[mansr]

I have mostly figured out the renderer, but there are still a few fields in the decoded stream metadata I don't know the meaning of. Could I ask that someone send me samples (a few seconds is enough) from a few different MQA files? I'd like a varied set, so please try to pick tracks from different labels, with different original sample rates, etc.

[audiventory]

Yes, but only in shitty electronics not worth having.

 

Digital pre-fitration can help even for «shitty electronics»

 

I'm much more concerned about for example 330 + 333 kHz or 1030 + 1033 kHz image harmonics.

For example when the digital filter outputs 352.8 kHz rate followed by zero-order-hold. When you play 1 kHz tone, the DAC will output both 351.8 and 353.8 kHz tones and thus intermodulation product of 2 kHz. And this is directly correlated with the input signal. This is further emphasized by the fact that at 350 kHz range the THD of analog sections will be higher, and thus also harmonic distortion products of these frequencies will cause also intermodulation products.

 

I’m agree.

 

With music, the level of 1 kHz tones is also generally much higher than 30 and 33 kHz harmonics.

 

I'm heard not once about harmonics in 30 … 40 kHz range with significant level. Probably it is artefacts of studio apparatus.

[mansr]

I have mostly figured out the renderer, but there are still a few fields in the decoded stream metadata I don't know the meaning of. Could I ask that someone send me samples (a few seconds is enough) from a few different MQA files? I'd like a varied set, so please try to pick tracks from different labels, with different original sample rates, etc.

 

Someone sent me a few samples, so thanks for that.

 

I'm still missing any "green-light" MQA files. If anyone has one, I'd appreciate a sample from it.

[abrxx]

Someone sent me a few samples, so thanks for that.

 

I'm still missing any "green-light" MQA files. If anyone has one, I'd appreciate a sample from it.

 

What does green light mean? Valid MQA but not officially approved by studio? I know Bob has explained before but it doesn't make much sense. I'd rather have a light that indicated a white glove remaster.

[mansr]

What does green light mean? Valid MQA but not officially approved by studio? I know Bob has explained before but it doesn't make much sense. I'd rather have a light that indicated a white glove remaster.

 

Sure, but for analysing the decoder it's better to have all kinds of inputs.

[Miska]

Digital pre-fitration can help even for «shitty electronics»

 

Although it can never substitute good analog reconstruction filters. But removing any content that originates from instruments is clear no-no. That's why I really don't like MQA's idea of starting leaky cut-off roll-off at 30 kHz while still leaking like hell at the Nyquist frequency.

 

ADC and reproduction must capture and reproduce everything from microphones like this:

http://www.sanken-mic.com/en/product/product.cfm/3.1000400

 

I'm heard not once about harmonics in 30 … 40 kHz range with significant level. Probably it is artefacts of studio apparatus.

 

Referring to my earlier link and other test I've been doing myself with percussive instruments, there's plenty of stuff going beyond that. For example violin creates wide harmonic spectra, as well as glockenspiel which I've been testing with.

 

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

[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

[audiventory]

Although it can never substitute good analog reconstruction filters. But removing any content that originates from instruments is clear no-no.

 

Referring to my earlier link and other test I've been doing myself with percussive instruments, there's plenty of stuff going beyond that. For example violin creates wide harmonic spectra, as well as glockenspiel which I've been testing with.

 

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

 

We don’t know exactly where is edge of accurate reproduction. Spectrum is infinite. So band should be infinite too, theoretically.

 

All spectrum limitations is measurement tools matter. New tools - new edge.

 

Band 100 kHz of apparatus limit spectrum too. Despite harmonics may be above.

 

At the Mansr’s picture the harmonics looks like wrong products, not harmonics of instruments.

 

[ATTACH=CONFIG]32642[/ATTACH]

 

I suppose, these wrong harmonics have much higher level than harmonics of musical signal.

 

As rule, we can hear lower 16 … 20 kHz. We can test it.

 

But where proofs of the edge of reconstruction?