I'm sure I could do this before in ACL3, how do I do it in ACL2013?  Some of my music is from old LPs that were themselves mono.  Some is stereo.  It needs to all be in mono or else I will get pronounced volume differences when a CD is played in the ice skating arena, where most sound systems are only mono. Then, if some songs are mono and some are stereo the mono ones will be much louder.  I need to be able to hear all the songs in mono before I export so I can check the volume levels.