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xandcg
Rio de Janeiro, BR.
Posts 218
Joined on 09-07-2014
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Post #:
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7
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Post ID:
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22290
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Reply to:
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21483
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fiogf49gjkf0d I found this description of how MQA works:
http://www.hifiwigwam.com/showthread.php?127311-Tidal-Announce-MQA-Streaming&p=2217736&viewfull=1#post2217736
It is not a secret, what MQA is and does.
Here we go, in decreasing levels of abstraction.
1) MQA is a kind of origami.
That doesn't help you.
2) MQA is about substituting triangles for rectangles.
That probably doesn't help either, although it is a brilliantly succinct way of describing MQA.
3) A bit more practical then.
Start (ideally) with a 192/24 recording.
Reduce this to 96/24 by means of a very short (i.e. fast) low pass filter.
Such a filter allows some aliasing to happen, but since we assume that there is not
much real audio in the 48-96kHz region the amount of aliasing is low.
Now take the 96/24 recording.
Grab the lower 24kHz band, at 24 bits, and noise shape it into a 48k/16b format.
Put the result in a 48/24 container. Hey, we now have 8 unused bits per sample!
Go back to the 96/24 original. Grab the upper band, i.e. 24 to 48kHz. Resample it at 48kHz.
This is lossless because the sampling theorem says that any signal with a bandwidth smaller than Fs/2 can be
sampled at Fs. So we end with the ultrasonic information in a 48/24
format. We now assume that, again, there isn't really much ultrasonic
info at all, so why let it occupy 24 bits? Not needed, so slam it down
to 8 bits. We now have 48/8. Scramble these into pseudo noise and store
the result in the lower bits of the 48/24 container we created in the
previous step.
Voila: 192/24 packed into 48/24.
For replay: undo in reverse order.
Very smart. Utterly useless |
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Think for yourself, do not be sheep.
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