[LAU] ABX test invite

Peder Hedlund peder at musikhuset.org
Sat Apr 6 01:03:31 UTC 2013


Quoting Ralf Mardorf <ralf.mardorf at alice-dsl.net>:

> FWIW I'm only experienced with stereo, not with 2D or 3D and I guess
> most engineers are inexperienced with 2D and 3D, however, assumed MP3
> can be used for stereo, it would be interesting to know, if MP3 or
> another codec with inaudible loss, is able to keep the mix for a real 2D
> or 3D recording. I don't know how data reduction does work, but I guess
> there's an effect similar to a compressor (the effect app or device).

No, data reduction in MP3, Vorbis, Opus, AAC or any of the other  
technologies is not just like a regular compressor in any way, shape  
or form.
Neither in the way of a 3:1, soft knee at -18 dB compressor or in the way  
of a "repeat this 0101 pattern 24 times" zip file.
It's exploiting the psychoacoustical fact that the sensitivity of our  
ears depends a lot on which frequency we're listening to and that a  
strong signal in one frequency completely masks a weak signal nearby  
to our ears.
So if you have a -20 dB signal at 7kHz at the same time you have a  
-5dB signal at 7.2kHz you can discard the former one since we won't  
hear it anyway.

There is an extension to MP3 called MP3 surround which is able to  
handle 5.1 surround sound (2D and 3D are image formats, not audio  
formats).

  - Peder


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