im attempting to make my own subliminal audiobooks however after turning the db down on the messages and keeping the music volume normal it was great until I converted to mp3 and it decided to increase the volume of my messages.
It’s MP3’s job to delete sounds, voices and other work which are too quiet to hear in normal songs or shows. That’s how it gets those small files. I expected the MP3 conversion to delete your subliminal messages, not make them louder.
In any event, that’s why many performers hate MP3. It re-mixes their work.
You might try saving the MP3 at a higher quality than the Audacity default of 128. I think you can choose higher values up to (I think) 320. Choose one super high value just to see what it does to your work.
Of course, you should be Exporting the originals as WAV. Those are your edit masters. Do Not save Master works in MP3.
If your target is mp3, you need to amplify to a maximum level of -3 dB peak. The mp3 encoder likes to add another dB of gain in most cases. Anything that is already heavily compressed will sound awful if it’s over -3 dB. Using a multi band compressor can help a lot too. But that takes time to tune.
With comments it won’t be as bad as the human voice has a limited frequency band, but transients in music will distort. Sometimes it sounds more or less OK with rock guitars, but very bad on sax, fi.
I am not quite sure of the extent of what you are trying to do, however, if it is for your own audio book, try this. These are the two options I can think of. Once you render to mp3, open the same file in Audacity and find the messages you want to make subliminal and De-amplify them OR create a second audio file and add it to your original file with a lower volume. This method is no different then adding background music to a voice over file.