Audio converter and editor

Audio converter

FreeStudio (e.g., convert from m4a to wav)

(Be careful not to install other software from the installer, if you think it gonna be useless for you)

http://pcsupport.about.com/gi/o.htm?zi=1/XJ&zTi=1&sdn=pcsupport&cdn=compute&tm=19&f=10&su=p284.13.342.ip_p504.6.342.ip_&tt=3&bt=8&bts=8&zu=http%3A//www.dvdvideosoft.com/free-dvd-video-software.htm

Audio Editor

Audacity