MQA technical analysis

[mansr]

I see a few advertising links being offered on this thread...

 

Permit me to offer a non-advertising link for those interested in some objective analysis:

COMPARISON: Hardware-Decoded MQA (using Mytek Brooklyn DAC)

 

Nice measurements. Everything I've seen suggests that the first stage decoding is identical on all devices, software or hardware. Certainly the Tidal decoder output is bit-identical to that of Bluesound one. The lowest bit of this output contains instructions for the "renderer" on how to upsample further. This includes the original sample rate and which of 16 predefined filters to use (I've only seen a few of them chosen in actual MQA files). These filters generally have a fairly slow descent towards a notch at 88.2 kHz which explains the difference you noted between software-only and full decoding. The "rendering" actually removes some of high-frequency content reconstructed by the decoder. Some graphs here: http://www.computeraudiophile.com/showthread.php?p=627196

 

After upsampling, the renderer truncates the signal to 16-20 bits (16 in all files I've checked) using shaped dither. The rising level you noted above 60 kHz is this dither noise.

 

Good job on the examination of the underlying code, everyone. Perhaps I missed it in this thread, but I am curious about the filter being used by the MQA decoder. Was there an updated sine sweep looking at the aliasing/nonlinear distortions?

 

The decoder uses a variety of filters for different purposes, not all of which I have figured out yet. The renderer uses filters as discussed around the post linked above.

[jmudrick]

I see a few advertising links being offered on this thread...

 

Permit me to offer a non-advertising link for those interested in some objective analysis:

COMPARISON: Hardware-Decoded MQA (using Mytek Brooklyn DAC)

 

Good job on the examination of the underlying code, everyone. Perhaps I missed it in this thread, but I am curious about the filter being used by the MQA decoder. Was there an updated sine sweep looking at the aliasing/nonlinear distortions?

A special thanks for also providing your listening impressions.

 

Sent from my Nexus 5X using Tapatalk

[Fokus]

Not related to the signal processing, but to the format itself.

 

MQA seems sensitive to ID3 tag contents. I took an MQA wav file, and converted it to flac in two flavours: one with ReplayGain writing to the ID3 tag, one without.

 

The Explorer2 refuses to recognise the ReplayGained track as MQA, even though the actual signal in the file nulls perfectly with the original MQA wav.

The Explorer2 is fine with the non-RGed track.

[mansr]

Not related to the signal processing, but to the format itself.

 

MQA seems sensitive to ID3 tag contents. I took an MQA wav file, and converted it to flac in two flavours: one with ReplayGain writing to the ID3 tag, one without.

 

The Explorer2 refuses to recognise the ReplayGained track as MQA, even though the actual signal in the file nulls perfectly with the original MQA wav.

The Explorer2 is fine with the non-RGed track.

 

Your player probably applied the gain thus destroying the MQA information. The DAC never sees the file headers (including metadata tags), so that alone can't make any difference.

[Fokus]

You are probably right.

 

Running all these experiments it is easy to forget a setting in Foobar. As to the DAC not seeing the header ... it seems that I also forgot to wake up today.

[audiventory]

I see a few advertising links being offered on this thread...

 

Permit me to offer a non-advertising link for those interested in some objective analysis:

COMPARISON: Hardware-Decoded MQA (using Mytek Brooklyn DAC)

 

I like in your article that you took several difference at same ADC. It allowed to check how to work measurement tool, for better sureness in results.

 

At point "2. How much difference was there between the "Reference" playback and "Hardware MQA" from the TIDAL stream?" we can see average difference -95 dB. Possibly it is about limits of the DAC+ADC system, possibly not. May be there difference tool limitation, may be not.

 

May be for purer checking ADC need to make several records for modeled tone and sweep sine PCM? And check dB-difference for captured and original signals.

 

I wondered about real measurement precision (difference in dB for the model signals) of the DAC+ADC system.

[mansr]

Can someone with an MQA DAC please play this file and report whether the indicator comes on and, if so, which colour.

mqatest.zip

[mm67]

Can someone with an MQA DAC please play this file and report whether the indicator comes on and, if so, which colour.

No MQA indicators and no sound

[mansr]

No MQA indicators and no sound

 

It was supposed to be silent. The purpose was to see if it actually detected the audio bits being tampered with while leaving the control bitstream alone. Apparently it does. Which DAC did you use?

[mm67]

It was supposed to be silent. The purpose was to see if it actually detected the audio bits being tampered with while leaving the control bitstream alone. Apparently it does. Which DAC did you use?

Explorer2

[The Computer Audiophile]

I see a few advertising links being offered on this thread...

 

Permit me to offer a non-advertising link for those interested in some objective analysis:

COMPARISON: Hardware-Decoded MQA (using Mytek Brooklyn DAC)

 

Good job on the examination of the underlying code, everyone. Perhaps I missed it in this thread, but I am curious about the filter being used by the MQA decoder. Was there an updated sine sweep looking at the aliasing/nonlinear distortions?

 

Hmm. A non-advertising link. That's kind of a play on words because you are making money through advertising on your site, and driving more traffic to your site through your posts on CA is clearly in your financial interest.

[mansr]

Hmm. A non-advertising link. That's kind of a play on words because you are making money through advertising on your site, and driving more traffic to your site through your posts on CA is clearly in your financial interest.

 

His post is informative and on-topic for this thread. It is not an advertisement for MQA, unlike those other links that were posted recently. Who cares if he makes a few cents off the traffic he gets from here?

[The Computer Audiophile]

His post is informative and on-topic for this thread. It is not an advertisement for MQA, unlike those other links that were posted recently. Who cares if he makes a few cents off the traffic he gets from here?

I think it's a bit comical that you guys don't trust the commercial interests of one entity, but do trust the commercial interests of another that supports your point of view.

[Melvin]

It was supposed to be silent. The purpose was to see if it actually detected the audio bits being tampered with while leaving the control bitstream alone. Apparently it does. Which DAC did you use?

 

No indicators and also silent using Bluesound Node 2. It shows 24/48 sample rate in the tech info.

[mansr]

I think it's a bit comical that you guys don't trust the commercial interests of one entity, but do trust the commercial interests of another that supports your point of view.

 

The ads I see on his site are served by Google and Amazon. I don't think they care whatsoever what he writes. This is very different from ads on, say, Audiostream where the advertisers have a direct relationship with the publication.

[The Computer Audiophile]

The ads I see on his site are served by Google and Amazon. I don't think they care whatsoever what he writes. This is very different from ads on, say, Audiostream where the advertisers have a direct relationship with the publication.

 

I disagree. Whatever you write about, Google will scrape the text and display ads that will garner the most clicks. Publishers frequently tailor their articles to discuss the topics that produce the best click through rates on the displayed ads. For example, if you talk about mesothelioma, you will make a lot of money. Lawyers will pay $50 per click to Google, who then cuts a percentage to the publisher.

[mansr]

No indicators and also silent using Bluesound Node 2. It shows 24/48 sample rate in the tech info.

 

Thanks for testing. I just wanted to confirm that the "authentication" really does verify the content of the file rather than just looking for the MQA control bitstream.

[mansr]

I disagree. Whatever you write about, Google will scrape the text and display ads that will garner the most clicks. Publishers frequently tailor their articles to discuss the topics that produce the best click through rates on the displayed ads. For example, if you talk about mesothelioma, you will make a lot of money. Lawyers will pay $50 per click to Google, who then cuts a percentage to the publisher.

 

I really don't think Google or Amazon are going to put pressure on random bloggers to write more favourably about things advertised through their networks. Looking at the post linked above, these are the ads I see:

 

- A book about DSP room correction at Amazon

- Amazon links for the products and music mentioned in the text

- Some sort of currency and/or commodity trading site

- Travelodge hotels

- Vinyl records from Amazon

- A Kindle reader from Amazon

- A "master class" on film scoring

 

Those are either completely random or triggered by a single keyword in the text. If you think that is in any way comparable to the highly paid ads placed by high-end audio companies on the usual "review" sites, you are out of your mind.

[Miska]

MQA seems sensitive to ID3 tag contents. I took an MQA wav file, and converted it to flac in two flavours: one with ReplayGain writing to the ID3 tag, one without.

 

The Explorer2 refuses to recognise the ReplayGained track as MQA, even though the actual signal in the file nulls perfectly with the original MQA wav.

The Explorer2 is fine with the non-RGed track.

 

Remember that one purpose of MQA is to allow decoded playback only in situations and environments tightly controlled by MQA. So you cannot apply any DSP of your choice; like replay gain, digital room correction, headphone cross-feed or stuff like that, unless those are specifically approved/blessed by the MQA company.

[The Computer Audiophile]

I really don't think Google or Amazon are going to put pressure on random bloggers to write more favourably about things advertised through their networks. Looking at the post linked above, these are the ads I see:

 

- A book about DSP room correction at Amazon

- Amazon links for the products and music mentioned in the text

- Some sort of currency and/or commodity trading site

- Travelodge hotels

- Vinyl records from Amazon

- A Kindle reader from Amazon

- A "master class" on film scoring

 

Those are either completely random or triggered by a single keyword in the text. If you think that is in any way comparable to the highly paid ads placed by high-end audio companies on the usual "review" sites, you are out of your mind.

 

Think bigger. Google doesn't put pressure, the advertising income can put pressure on people. If you write about music, then you'll see Adsense ads for people selling music. One only has to look at the Adsense stats to see which ads are paying him the most, and tailor his content to talk more about the stuff that brings in more income.

 

I'm not suggesting this happens on his site, I'm only suggesting that it's a bit strange for people to suggest advertising on other sites matters, but advertising on his site that supports your view point doesn't matter. that's all.

 

I'm not suggesting his income is comparable (your word) to the other sites.

[Samuel T Cogley]

Think bigger. Google doesn't put pressure, the advertising income can put pressure on people. If you write about music, then you'll see Adsense ads for people selling music. One only has to look at the Adsense stats to see which ads are paying him the most, and tailor his content to talk more about the stuff that brings in more income.

 

I'm not suggesting this happens on his site, I'm only suggesting that it's a bit strange for people to suggest advertising on other sites matters, but advertising on his site that supports your view point doesn't matter. that's all.

 

I'm not suggesting his income is comparable (your word) to the other sites.

 

 

Hi Chris. With due respect, I think you're beating around the bush a little. A better way to say that is that his blog is not his "day job".

[mansr]

Think bigger. Google doesn't put pressure, the advertising income can put pressure on people. If you write about music, then you'll see Adsense ads for people selling music. One only has to look at the Adsense stats to see which ads are paying him the most, and tailor his content to talk more about the stuff that brings in more income.

 

The Amazon link for, say, the RME Fireface appears regardless of what is said about it in the text. In fact, you often see these content-related ads pop up in the most ironic of situations, i.e. right next to a scathing criticism of whatever the ad is for.

[smartin]

Think bigger. Google doesn't put pressure, the advertising income can put pressure on people. If you write about music, then you'll see Adsense ads for people selling music. One only has to look at the Adsense stats to see which ads are paying him the most, and tailor his content to talk more about the stuff that brings in more income.

 

I'm not suggesting this happens on his site, I'm only suggesting that it's a bit strange for people to suggest advertising on other sites matters, but advertising on his site that supports your view point doesn't matter. that's all.

 

I'm not suggesting his income is comparable (your word) to the other sites.

 

I would just add that from my reading, the linked article doesn't really support mansr (or contradict for that matter). It talks about potential DRM (referring to mansr's work I believe) and is skeptical about deblurring (both from an analysis standpoint and listening), but mainly it points out how MQA is actually delivering a really good facsimile of the original master, both objectively and from listening.

 

I would say the main thing the article does is put the lossy aspect of MQA in perspective, that the resultant noise (compared to the original) is incredibly low energy (arguably inaudible.)

[daverich4]

Any chance we could get back to the topic of this thread and move the discussion of web advertising to a different thread or even a different forum?

[mansr]

We've all seen the characteristic noise hump in undecoded MQA files. Apparently, this is the result of shaped dither applied during the encoding. The first two steps of the decoding process entail removing part of this noise. This is possible since the pseudo-random sequence used to generate it is known. Here's a graph of the decoder in action: