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MQA pt II

Jim Audiomisc said:
OK, I've just put up a new page on this at http://www.audiomisc.co.uk/MQA/questions/QuriousAssumptions.html

Note that it is just a section of what I'm doing at present, so a 'page 1' based on measurements I've been making. I didn't want the page to get too long, or keep delaying making the first parts of the results, etc, becoming available. I'll be working on other aspects of this and will put up another page about them when ready.

My 'objective' is quite simple. It is to apply the usual methods of science and engineering to probe the claims made, and the actual behaviour of, the MQA system. The aim being to provide evidence based on measurement and scientific analysis which people can then see and consider to help them come to their own conclusions, etc. i.e. SOP for scientists and engineers.

More to come... :)
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Thanks read quickly yesterday now more slowly. One question-
"The spectra on the right shows the output when a sox-upsample to 88k2/24 was played, thus causing the DAC to treat it as plain LPCM, and the MQA indicator did not light up" -should that read "the spectra on the left *..."?

*possible bonus erratum "show" not "shows"
 
Werner said:
single: spectrum
plural: spectra

and while we're at it
single: stylus
plural: styli

(One can't suppress 12 years of Jezuit college education.)
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The word "spectra" is correctly applied as there are 4 of them, it's just that the verb doesn't agree. But I'm sure Jim knows this, he just has his mind on more important matters.
Incidentally I have noticed that scientists (at least English ones) tend to be particularly scrupulous in using verbs in the plural with data ("the data do not show any recognisable trend").
 
Jim Audiomisc said:
The specific tests I do then give specific results. By doing a variety I can start to 'box in' the claims and find any contradictions, etc. Given a set of vague and sweeping claims, internal contradictions become useful as way to find that at least *some* of the claims must be shakey. :) You can't have your kayak and heat it...

The 'bumps' show some of the artifacts. This alters in the output, but remains, and seems *very* unlikely to be a common feature of the source material prior to MQA encoding.

One of the reasons I'm looking at making (linear) corrections to the added dispersion, etc, is to help untangle linear changes from non-linear or added-subracted artifacts that are harder to detect because the dispersion, etc, make a simple 'sample-by-sample-diff' fail to show the nonlinear differences. (I'm also looking at other ways of doing that.) However like steganography, that can be a long game.

Your pointing out what some DACs do, is useful. I will try to look at that. However when I play the 'tailed' files the MQA led does go out during the tail being played. So it does detect - after a delay - that the material isn't MQA. But as you indicate that doesn't mean the decoder isn't still applying at at least some MQA changes. So thanks for pointing out the other DACs. I'll have a look at this for the Explorer 2. It would be very handy for investigation if it will leave the decoder on for long periods.

MQA wanting this for gapless reasons seems weird to me. It impies non-MQA files will get 'faked' alterations applied. If I were a user I'd not be delighted by that. Can you list some of the DACs that do this and point me at any details?

I'll be doing more tests on the Explorer 2 anyway. e.g. want to check what happens when the internal gain is wound down 6dB. As it stands it can't cope with 'overs' very well so want to see if that fixes the limitation.

And - as always - I encourage you and others to do your own tests to investigate. e.g. if someone is using roon to decode MQA see if you can capture the output or apply changes to it to undo the dispersion, etc. Given what I've seen thus far I suspect that using even a fairly 'budget' ADC like the Scarlett 2i2 3rd Gen would yeild useful data. (I have one of these and it works fairly well. Just not in the ADC1 class - but of course, only a fraction of the price!)
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The DAC that I remember being faulted for keeping the MQA filter as default for non-MQA material is Mytek Brooklyn, but I can't readily find a reference. Unhappy owners disabled MQA decoding to defeat this. I owned one for a while and sold it - just never warmed up to its' sound. Here is a measurement set that you may find interesting:

https://www.stereophile.com/content/mytek-hifi-brooklyn-da-processor–headphone-amplifier-measurements

The other unit I suspect is setup this way is Mytek Liberty (which has just been displaced out of my DAC stable to make room for the new HDCD DAC). It has an uncharacteristic sound to the generation of ESS DAC chips that it uses.

I think your task will be easier if you had known good LPCM equivalents. I still think that a professional contact to 2L is well worth pursuing.
 
adamdea said:
Thanks read quickly yesterday now more slowly. One question-
"The spectra on the right shows the output when a sox-upsample to 88k2/24 was played, thus causing the DAC to treat it as plain LPCM, and the MQA indicator did not light up" -should that read "the spectra on the left *..."?

*possible bonus erratum "show" not "shows"
Click to expand...

Guilty, m'lud. I throw myself at the mercy of the court...

Now fixed I hope. I omitted my standard "there will be typos" warning, so this kind of thing was inevitable.
 
Here you may download a Springsteen live tour box set as MQA priced the same as hi res FLAC-HD and ALAC-HD.
khQvjMhl.png
 
You cannot make a silk purse out of a sows ear.

You can upsample,MQA,Hi Res,DSD,HDCD or whatever sausage machine you like to pass your material through.

If it has not been engineered and mastered correctly at the recording stage it is always going to sound sub standard.

Like a shit sausage...
 
I've been spending some time 'catching up' with other things I need to do. All being well, I'll be though that in a few days. However I've continued to poke about into MQA-related issues - mainly temporal. :) One result people may find interesting as a 'taster' from a wider examination:

http://jcgl.orpheusweb.co.uk/temp/sinc-vs-mic.png

This compares the ideal textbook assumption of hitting an ADC-DAC chain with a perfect impulse with what you get with a 'typical' microphone. They are, erm, slightly different. Does make it seem odd to obsess about any need to 'disperse' the data to avoid 'pre ringing'. (Which is also widely misunderstood.)

The plots assume 96k sampling. The mic is assumed to have a familar 'ring and die' HF response that many studio mics over the years show - when the makers provide data on them, and assuming it is even close to the reality!
 
kaolin said:
MQA files should be the same price for CD digital 16/44.1 regardless of the source
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Personally, I think MQA files should be cheaper than a good CD version that hasn't been tarted up. I doubt my view on that will surprise anyone, though, as my main preference would be to not buy MQA processed material anyway - given the choice. What others do, is up to them.
 
Jim Audiomisc said:
I've been spending some time 'catching up' with other things I need to do. All being well, I'll be though that in a few days. However I've continued to poke about into MQA-related issues - mainly temporal. :) One result people may find interesting as a 'taster' from a wider examination:

http://jcgl.orpheusweb.co.uk/temp/sinc-vs-mic.png

This compares the ideal textbook assumption of hitting an ADC-DAC chain with a perfect impulse with what you get with a 'typical' microphone. They are, erm, slightly different. Does make it seem odd to obsess about any need to 'disperse' the data to avoid 'pre ringing'. (Which is also widely misunderstood.)

The plots assume 96k sampling. The mic is assumed to have a familar 'ring and die' HF response that many studio mics over the years show - when the makers provide data on them, and assuming it is even close to the reality!
Click to expand...

To get an impulse response for an actual microphone one method is to record a generated high voltage spark. This is about as harsh an impulse as you are likely to easily get. Having very little low frequency info you would not need a huge amount of absorption to make the result virtually anechoic.
 
Werner said:
A collection of microphone impulse responses: http://micirp.blogspot.com/. Sadly mostly ancient models, and limited to 44.1kHz.

Another method for measuring a microphone is, allegedly, popping a balloon.
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I'll have a look. I do have some impulse responses from various 'sources'. Howeve mics vary a lot, and the result depends on other factors. So for simplicity I've just used what seems to be a 'sort of typical' behaviour. To be kind I ignored the LF roll-off and only included the common main HF resonance. This seems sufficient for the main point - that they generally are nothing like the sinc shape and swamp a 96k inpulse.

Doing it this way also let me well-define the impulse instant to show that the response is essentially causal.

I am going on to point out that real filters all have to delay the signal. So in reality, 'pre ringing' is *also* causal... when you can find it in real audio as distinct from "compute a single nonzero sample surrounded by zero samples" impulses.
 
Puggie said:
To get an impulse response for an actual microphone one method is to record a generated high voltage spark. This is about as harsh an impulse as you are likely to easily get. Having very little low frequency info you would not need a huge amount of absorption to make the result virtually anechoic.
Click to expand...

In practice the only bit that will matter much is below or a bit above the first HF resonance. Above that, the mic filters away. Real impulse responses on mechanical systems also risk the peak out-of-band HF generating nonlinearity. Which adds yet another complication. So I'm not going to try to get one from the few mics I have (which aren't studio grade anyway!)
 
You've now got me wondering how the results vary if you use a 'spiral' long balloon or a long balloon shaped as a poodle. 8-] Did Henze specify this? Can we create a new instrument that uses an array of variously shaped and sized balloons?...
 
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