[X4U] How To Anti-Encode Audio File

[Alex]

On Apr 24, 2005, at 17:11, DZ-Jay wrote:

> On Apr 24, 2005, at 16:57, Alex wrote:
>
>> My understanding is that Audacity <http://audacity.sourceforge.net/> 
>> is not an MP3 editor as such. By "MP3 editor" I mean a tool which 
>> edits an MP3 file _without_ decoding it (e.g., MP3 Trimmer). AFAICT, 
>> what Audacity does is import (i.e., decode) an MP3 file (using 
>> madlib), edit the resulting audio file, and then re-encode it to MP3 
>> (if an MP3 encoder is installed). In other words, what all audio 
>> editors do.
>
> I believe that in order to edit an MP3 file you *need* to decode it, 
> as the MP3 algorithm includes compression.

No. Herein lies the distinction between an audio editor and an MP3 
editor. Anything that decodes an MP3 to edit it is not an MP3 editor.

As to what an MP3 editor does, you have to understand that an MP3 file 
is comprised of discrete frames (each with its own header). Frames can 
be manipulated _without_ decoding. There are, of course, limits on what 
can be done within these constraints; for instance, frames are not 
necessarily independent, and it may not be possible to discard (trim) 
single frames; more importantly, any kind of editing that has to be 
done on the waveform itself (e.g., applying a noise gate) is not 
possible.

Further reading:

<http://www.id3.org/mp3frame.html>
<http://www.mp3-converter.com/mp3codec/>
<http://www.mp3-tech.org/>


<0x0192>