Audacity will decompress when you open the file.
. I have done Normalize> Peak value>Treat each channel Independently, thinking that should do it, but the imbalance persists. What next?
The peaks don't necessarily correlate with loudness.
Matching the RMS levels should work better (and if that doesn't work you can do it by ear).
Download and install the
ACX Check plug-in. It will appear under the
analyze menu, and it will give you the RMS levels for left & right as well as some other "numbers". (You can ignore the pass/fail information, that's for audiobooks.)
After running Normalize independently,
Run ACX check and subtract the RMS levels to find the dB difference.
Click the drop-down arrow to the left of the waveform and select
Split Stereo Track. (That allows you to adjust left & right separately).
Select the "louder" channel and then
Amplify by the dB difference (entering an negative number so you are attenuating instead of amplifying).