Flac - Dec 2010 - FLAC suddenly compresses more - why?

Hello Rene,
If you want to be sure that you get no information loss, I suggest a very simple
test. Recover your WAV file from any of the FLAC files you mentioned in your
e-mail. If this WAV file is bit-by-bit identical to the input WAV file, then you
have no information loss.
Also, it is important to take into account that the compression ratio is highly
dependent on the encoded wav file. If you are processing CDs, the compression
ratio?for rock and pop music?is tipically 45 % to 70 %. For other kinds of music
such as jazz, the compression ratio may be from 25 % to 40 %.
What kind of music have encoded so far?
Regards,
Fernando A. Marengo Rodriguez, PhD

Acoustics and Electroacoustics Laboratory

School of Electronic Engineering

Faculty of Sciences, Engineering and Surveying

National University of Rosario

Rosario, Argentina


      
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On Dec 27, 2010, at 07:10, Fernando Alberto Marengo Rodriguez
wrote:
> If you want to be sure that you get no information loss, I suggest  
> a very simple test. Recover your WAV file from any of the FLAC  
> files you mentioned in your e-mail. If this WAV file is bit-by-bit  
> identical to the input WAV file, then you have no information loss.
This is a good test, but keep in mind that only the audio part of the  
WAV file will be identical.  There are non-audio parts to a WAV file,  
and those may be lost or changed when compressed, so you will need  
some method of comparing only the audio and not the rest of the  
file.  In other words, a basic file to file compare might fail even  
if the audio is the same.

I'm not sure how to compare the audio part only, at least not  
easily.  You can place each file in the same DAW, but with one set  
for inverted polarity.  Then mix them together and you should get  
silence.  But that is not an easy or simple test.

Brian Willoughby
Sound Consulting

On Mon, Dec 27, 2010 at 6:21 PM, Brian Willoughby <brianw at
sounds.wa.com> wrote:
> This is a good test, but keep in mind that only the audio part of the
> WAV file will be identical. ?There are non-audio parts to a WAV file,
> and those may be lost or changed when compressed, so you will need
> some method of comparing only the audio and not the rest of the
> file. ?In other words, a basic file to file compare might fail even
> if the audio is the same.
>
> I'm not sure how to compare the audio part only, at least not
> easily. ?You can place each file in the same DAW, but with one set
> for inverted polarity. ?Then mix them together and you should get
> silence. ?But that is not an easy or simple test.
Use raw files. E.g. the --force-raw-format with the flac command line command.

> On Dec 27, 2010, at 07:10, Fernando Alberto Marengo Rodriguez wrote:
>> If you want to be sure that you get no information loss, I suggest
>> a very simple test. Recover your WAV file from any of the FLAC
>> files you mentioned in your e-mail. If this WAV file is bit-by-bit
>> identical to the input WAV file, then you have no information loss.
>
> This is a good test, but keep in mind that only the audio part of the
> WAV file will be identical. ?There are non-audio parts to a WAV file,
> and those may be lost or changed when compressed, so you will need
> some method of comparing only the audio and not the rest of the
> file. ?In other words, a basic file to file compare might fail even
> if the audio is the same.
>
> I'm not sure how to compare the audio part only, at least not
> easily. ?You can place each file in the same DAW, but with one set
> for inverted polarity. ?Then mix them together and you should get
> silence. ?But that is not an easy or simple test.
Caveat: I've never tried any of these, but these have come up in
various HA threads I've read over the years:

Audacity
EAC: Compare WAVs (CTRL-W)
foobar2000: bit-compare two tracks
(http://www.foobar2000.org/components/view/foo_bitcompare)

Cheers,

Martin