instead of deleting duplicates of my Voicememo because it seemed too complicated, I just lost patience and deleted them all by deleting all files ending in .m4a, but that included all music that came from CDs. How can I bring them back?
If you've emptied the trash, you're pretty much out of luck. However, you say that the music in question came from CDs; assuming that they are your own CDs, just re-import into iTunes. If not, hopefully you have a backup of your data somewhere that will allow you to restore the deleted files. In the future, exercise patience and caution!