iTunes does the jobAfter quite a while trying this and that, I finally found out that iTunes will do the job. This is what you have to do:
Set up iTunes
- Choose iTunes > Preferences > General
- Click the dropdown choice button, Importing preferences (never mind it's associated with When a CD is inserted, ignore that)
- Click Import using: and select your choice of format from the dropdown list. I use AIFF, high quality and seems to be fine for burning to CDs or playing in iTunes or on an iPhone.
- The Setting: seems to want to be automatic.
- Click OK, and OK in the Preferences pane.
Convert your music file
- Import your m4a (or other format) music file into iTunes
- Highlight to select it
- Right click - and you have a choice to Create AIFF version - iTunes will make an AIFF copy for you.
- To see it in a Finder folder, right click again and select Show in finder.
Edit your music fileThen you can locate your converted file, open it in Audacity, and edit and save it in the usual way.
Credit where credit's due, http://support.apple.com/kb/ht1550 does sort of explain all this.