I run a dual boot system with Ubuntu 19.10 and Windows 10 Professional. I create special audio files, and one form of the file has stereo, where channel 2 is the invese of channel 1. When I export an MP3 in Ubuntu 19.10 Audacity V. 2.3.3 I get an mp3 with stereo as created.
When I load the stereo mp3 into Audacity 2.3.3 in Windows 10 Pro and export the file, it combines the stereo into mono, and since the two channels are just the inverse of the other, the two zero out, so that I have recorded a blank channel.
BTW: absolutely love Audacity, have been using it for years, for this exact same purpose, so I know something ws not right when exporting stereo mp3 from Audacity 2.3.3 in Windows 10 Pro Phil
When I load the stereo mp3 into Audacity 2.3.3 in Windows 10 Pro and export the file, it combines the stereo into mono
Audacity 2.3.3 has an MP3 Export Option called Force Mono.

Koz
Thanks Koz, perfect fix. I have been avoiding creating the interference on Windows 10 Pro, but now that is unnecessary… Phil
“Joint Stereo” should give you better quality (or a smaller file with variable bitrate) because with L+R and L-R are compressed/saved separately. Since L+R is silent it will use much less file space.
I create special audio files, and one form of the file has stereo, where channel 2 is the invese of channel 1.
As you know, you’ll get silence when played in mono (like on a phone speaker). And with speakers the bass soundwaves will cancel.