Do repeated exports of same MP3 file degrade quality?

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Do repeated exports of same MP3 file degrade quality?

Permanent link to this post Posted by WadeCottingham » Fri Jul 10, 2009 1:38 am

Hello!

My question has to do with how
EXPORT works. Short version:
If I keep opening and exporting
the same mp3 file at 320 each
time, for like 10 times in a row,
does the conversion to mp3
each time degrade the sound
quality? OR would the exported
mp3 file be exactly the same each time
(assuming I made no changes before exporting)?

Long Version:
If I take an mp3 file recorded at 320 and open
it in Audacity, and edit it,
say snipping a few seconds off the end of the file,
and then export it at 320, and then
repeat the process...... open the file I just exported,
and snip a few seconds off the end, and
export it at 320 ..... repeat the process several times.

If I repeat this process 10 times, is the tenth
export of a lower quality than the original file?

I'm trying to understand if each cycle of opening,
editing, and exporting a file results in degradation like analog tape bounces
would ..... or does Audacity preserve the exact
digital file when exporting (minus the parts I chopped off).

If this question makes sense, the answer would
help me so much with my current recording / mastering
project, so thank you in advance !!

Wade Cottingham
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Re: Do repeated exports of same MP3 file degrade quality?

Permanent link to this post Posted by kozikowski » Fri Jul 10, 2009 2:49 am

If you repeatedly export edited versions of one Audacity Project, then the damage will be the same at each export, more or less. Audio compressors look at the Whole Show and not piece by piece, so if you made the show shorter, you might get a different compression. In the higher order compressors (not MP3) you may get a really different compression.

If you chain export > import > export > import > export > Import, damage adds up. Each export is compressing the damage of the step before. Production compressors always assume that the show being presented to them is perfect, and they take steps to preserve the quality -- always missing it a little depending on the settings. In your case, each step will preserve the damage and miss that a bit each time. So you get broken damage.

WAV and AIFF are the production formats, MP3 and other compression products are delivery formats. They don't cross well at all.

There are editors out there that edit MP3 without decompressing. Their tool set is very restricted; cutting, copying, deleting. No noise reduction, no tone controls.

Koz
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Re: Do repeated exports of same MP3 file degrade quality?

Permanent link to this post Posted by WadeCottingham » Sat Jul 11, 2009 12:18 am

Perfect answer, thank you so much.
I need to be using WAV files for what I'm doing.
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Posts: 2
Joined: Fri Jul 10, 2009 1:31 am

Re: Do repeated exports of same MP3 file degrade quality?

Permanent link to this post Posted by kozikowski » Sat Jul 11, 2009 12:29 am

The down side to doing that is they're big. People are stunned to find their 35MB hour-long stereo show converts to a 700MB wav file.

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