[SATLUG] mp3 encoding

Jeremy Mann jeremymann at gmail.com
Wed Oct 29 08:58:46 CDT 2008

On Wed, Oct 29, 2008 at 8:53 AM, Borries Demeler
<demeler at biochem.uthscsa.edu> wrote:
>> Naturally, you'd want to edit the original WAV file and export that as
>> an MP3.
> My question was about starting with an MP3 file, not a WAV file. Of course
> I would edit the wav file if I had the option. I want to know if Audacity
> uses exactly the same MP3 encoding as the original for the unedited portions
> of the file, or if it would try to re-encode it (with a loss). For example,
> you can load a jpg or mp3 file and write it back unchanged, or simply chop
> a portion of the file out without doing anything to other portions of the
> file. And I want to know if Audacity can do that.

It will reencode the entire file again at whatever bitrate you choose.

>From their wiki:

"Every time you export from Audacity as an MP3 (or other lossy audio
format), this encoding necessarily degrades some of the original
quality of the audio. If you import an MP3 into Audacity, edit it then
export it as an MP3, you are thus losing quality twice - once in the
original MP3 encoding of the imported audio, then again when you
export it from Audacity as MP3.
If you can't avoid importing an MP3 into Audacity and then re-encoding
to MP3, don't believe what you sometimes hear that using the same or
higher bit rate as the original file will prevent quality loss. This
is incorrect. All you can say is that the higher the bit rate you
re-encode to, the less will be the quality loss that results."

Jeremy Mann
jeremy at biochem.uthscsa.edu

University of Texas Health Science Center
Bioinformatics Core Facility
Phone: (210) 567-2672

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