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gmgraves

What does the second and third “unfold” of MQA files actually do?

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If the first unfold, generally done in software such as the Tidal app, Audnirvana, and Roon outputs files of either 88.2 or 96 KHz sampling rate, what do the second and third unfolds from the Renderer do? I called AudioQuest, and was dumbfounded to find that their technical guy didn’t know! He suggested I contact MQA in England. But before I do that, I thought I’d ask here. Thanks in advance for any help on this issue.


George

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1 hour ago, mansr said:

The first "unfold" decodes compressed data hidden in the lower 8 bits of the 24-bit MQA stream. The output has twice the sample rate of the input.

 

The second "unfold" is a trivial upsampling using one of 16 predefined filters as indicated in MQA metadata. We know how to decode this.

 

There is no third "unfold." Anyone claiming otherwise is either a liar or repeating lies.

Thanks. The notion of a “third unfold”, I got from the MQA website. They talk about it but don’t say anything other than that the renderer does the second and third unfold and gives the listener the audio that is exactly what the engineers and producers heard from the studio playback. 
So what you are saying, if I understand you properly, and I respect your knowledge, is that the Core Decode is really all one needs for MQA playback.


George

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4 minutes ago, gmgraves said:

So what you are saying, if I understand you properly, and I respect your knowledge, is that the Core Decode is really all one needs for MQA playback.

That is correct.

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8 hours ago, mansr said:

The first "unfold" decodes compressed data hidden in the lower 8 bits of the 24-bit MQA stream


Other than unpacking compressed data does the “first unfold” apply any proprietary DSP as well?  In other words is there a reason why you might anticipate that it would sound different from a straight  24/96 file?  

 

I also note that some MQA files stay as “24/48” after the initial decode, what’s going on (or not going on) there?

 

Thanks.

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20 hours ago, mansr said:

The second "unfold" is a trivial upsampling using one of 16 predefined filters as indicated in MQA metadata. We know how to decode this.


For some reason I vaguely remember reading a long time ago in this thread that filters 9-16 are actually just duplicates of 1-8? Or, I could have just dreamt it. 

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20 hours ago, Norton said:

I also note that some MQA files stay as “24/48” after the initial decode, what’s going on (or not going on) there?

 

This is what XXHighEnd would show you, when it is so. It is my understanding that the current "standard" (a convention) depicts that there's always an upsampling step in order when the file is under 88.2 sampling rate. I (XXHighEnd) don't comply to that ... (and you (XXHE) would upsample yourself anyway, per your own means and up to the rate your DAC can handle).


Lush^2      Blaxius^2      Ethernet^2     HDMI^2

XXHighEnd (developer)

Phasure NOS1 24/768 Async USB DAC (manufacturer)

Phasure Mach III Audio PC with Linear PSU (manufacturer)

Orelino & Orelo MKII Speakers (designer/supplier)

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