.aup3 file 30x bigger than source!?

I recently used Audacity to reduce some noise in an audio recording.

• The source file was an 51 MB .mp3 (60-min @128kb)
• I ran a single noise reduction pass over the audio and exported it back out
• The export .mp3 file was 51 MB (just like before)
• I had to try 2-3 the different noise reduction settings (various dBs, etc) so I thought I would save the Audacity .aup3 file in case I needed to tweak the noise reduction
• I could not believe or understand it I saw that the .aup3 save was 1480 MB (1.48GB)

I read a few posts and it seems like this is not super uncommon but I had to ask about it…
• Why on earth is the .aup3 file so massive, and so much bigger than the source?
• Surely at most it just needs to be: copy of source file (51MB) + record of transformations applied (1KB)?
• Did I do something wrong / is there some way to compress the .aup3 file?

… Hopefully I can figure this out, as otherwise it literally isn’t worth me ever saving an .aup3 file, as I can’t afford to be taking up GB after GB, just to save the edits to a few 50-60MB files.

Project files are 32-bit floating point uncompressed. In WAV format that would be more than 20X the size of a 128kbps file. The project has some overhead and maybe copies of the data for “undo”.

The project is only for “temporary” use and it can only be opened in Audacity.

You can also save as a temporary 16-bit WAV which will be about 10 times the size of your MP3. If you are making multiple edits/changes and you want to save temporary files, it’s a good idea to save lossless files because some “damage” accumulates with every generation of MP3.

FLAC is lossless compression and a 16-bit FLAC would be something like 6 or 7 times the original MP3.

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