[LAU] Audacity strange behavior

[Erik de Castro Lopo]

Folderol wrote:

> As a double blind test when seeing what changes were made to Wav files
> when translating to and from Flac, I also used Audacity to make a
> direct copy using 'Export'.
> 
> To my surprise, the copy had a different md5sum signature.
> 
> Thinking that the export operation might be creating the differences I
> exported another copy, but this turned out to have a different
> signature to both the previous ones. A third copy was again different
> to all the others.

WAV files have a header as well as the audio data. Its highly
likely that the audio data is the same each time and that the
header is different.

> Listening to the files I could detect no difference, nor could i see
> any difference in Audacity, even when stretching the display enough to
> see the actual waveforms.
> 
> It occurred to me that the differences might be due to some sort of
> timestamp embedded into the file header (I don't really know what
> meta-data Wav files contain)

They can indeed contain time stamps.

> so I looked at the files in a Hex editor,
> cecking at several identical locations through the files. They all
> showed up as different, and it wasn't just the same pattern but shifted
> a few bytes.
> 
> Can anyone suggest what might be happening here?

Can you put two example files that are supposed to be the same up on
a web server somewhere?

Also, I you grab the latest pre-release of libsndfile at:

    http://www.mega-nerd.com/tmp/

and compile it, you will find an example program called sndfile-cmp
in the programs/ directory which compares just the audio data.

Cheers,
Erik
-- 
-----------------------------------------------------------------
Erik de Castro Lopo
-----------------------------------------------------------------
"Using Java as a general purpose application development language
is like going big game hunting armed with Nerf weapons."
-- Author Unknown