Is it possible improve (modify) Audacity in such way, that it would have been allowed editing direct audio without decoding io PCM?
Basically no - but there are other apps available that will do simple MP3 editing with decoding/recoding.
One of them is MP3cut: https://sourceforge.net/projects/mp3cut/
And another: https://sourceforge.net/projects/mp3splt/
But there are several others I believe,
Is there nothing you can do? It would be good to develop in this direction in the future. The problem is obvious. After “import - export”, without any changing, the quality, though a little bit, becomes worse.
It is impossible to apply effects directly (without first decoding) to MP3 encoded audio other than extremely simple effects such as “amplify” and “fade”.
That’s not a direction that the Audacity developers want to go - it would make Audacity far too limited.
I understand. Nevertheless, releasing additional version of Audacity with the most limited functionality, but direct import/export would be great!
FYI - AAC (MP4/M4A) is pretty-much immune to accumulated compression damage. I don’t have the link handy but somebody did an experiment with 100 encode-decode cycles. MP3 was badly damaged but AAC wasn’t damaged at all.
Perhaps it depends on which AAC encoder is used. I’ve just tested exporting a test signal as AAC, importing it and then exporting again as AAC… repeating for 5 “generations”. Each generation shows small but measurable additional degradation.
The first encoding had the biggest loss, after which there’s about +1 dB “noise to signal” per generation.