[LAU] Lossy audio to lossless format

[Philipp Überbacher]

On Wed, 1 Oct 2014 10:54:33 +0200
Egor Sanin <egor.sanin at gmail.com> wrote:

> Dear community,
> 
> While not directly a linux related question,
> I am wondering about ultimately using linux
> tools for the possible solution, so:
> 
> I get the feeling at times, when getting music
> from torrents and such, that not all files
> claiming to be flac are actually lossless.
> It seems that sometimes folks will take an
> mp3, reencode it in flac and distribute the
> result.
> 
> Now the question is whether it is possible to analyze an
> audio file encoded in a lossless format and
> determine if it existed as a lossy file in a
> previous life?
> 
> Any insight is appreciated.
> 
> Thanks.

Hi Egor,

once upon a time I read a lot about audio codecs on
http://www.hydrogenaud.io/forums/. Note that this is a codec focused
forum, not a free software focused one, but people like the lame and
ogg developers do (or used to) read and write at those forums AFAIK. I
also remember that there was some windows tool for the purpose you
describe but I can't recall the name. Anyway, AFAIR it used the
techniques already described, spectral analysis to detect lowpass
filtering.

There are some artifacts of the mp3 codec that allow for rather
reliable detection, pre-echos come to mind. You are likely able to
train yourself to listen for these artifacts, but you may not be able
to un-train yourself ;)

Regards,
Philipp