Does Audacity convert MP3 to WAV before editing?

[arogers14]

If I change the audio level of an MP# file, does Audacity first convert it to WAV. make the level change, then convert back to MP3?

[steve]

Yes (sort of).
Audacity decodes the MP3 file to uncompressed data when it opens it. If you then Export as MP3, LAME will encode it back into an MP3 (assuming that you have lame installed).

Your next question - how do I edit an mp3 file without the sound quality loss of decoding and re-encoding?
Well the amount of editing that you can do on mp3's is limited, but for basic editing, try mp3DirectCut http://mpesch3.de1.cc/mp3dc.html

[arogers14]

Thanks. I suspected that. It seems to me that decoding then recoding is likely to cause some intermodulation distortion. I have no idea how significant that would be.

I've come across a program called MP3Gain that can normalize the levels of all the files in a folder without decoding then reencoding, but it has no other editing abilities. But it will satisfy my one need of normalizing my collections of dance music from various sources.

My other immediate need is for a good mp3 splitter to enable me to select portions of long, long performances. I thought that Audacity might be good for this purpose. I've had a trial version of a program called Direct WAV MP3 Splitter which did a good job at this task, but Audacity seems to allow finer resolution display of the waveforms. That looks like it would make it easier to split the files correctly. So far I haven't learned how to do that, since I just got a copy of the manual to work only a couple of hours ago.

But, back to the first question. If I use Audacity just for splitting, will I avoid the decoding, recoding process? Since Direct WAV MP3 Splitter doesn't do any other kind of editing, I believe that it probably doesn't decode.

[steve]

If I use Audacity just for splitting, will I avoid the decoding, recoding process?

No. Audacity always works on uncompressed audio.

mp3DirectCut will split mp3s without decoding - I'm not sure how much more that mp3DirectCut can do, but I hear it is good and quick for splitting MP3's with no change to the sound quality. Got to be worth a try - I believe it's a free program.