Audacity Forum

thanks, it works! and yes, saving mono files will save 50% of space approx (as expected)

for saving space and *before* conversion to AAC by FFMPEG. very easy in principle, looking here http://wiki.audacityteam.org/wiki/Talk:Mixing_stereo_tracks_to_mono_in_your_Project still, if I save the mono track and re-open it I still se two channels. I cannot fine any oprion which sets the mono bit...