Turning M4A audio into something everyone can open
What M4A is
M4A is an MPEG-4 audio file, usually AAC and sometimes Apple Lossless. It sounds good and stays small, and it works perfectly across Apple devices. The catch is that it does not always carry over to a work laptop, an old player or a friend’s phone.
Where M4A files come from
iPhone Voice Memos, GarageBand exports and iTunes or Apple Music downloads are all M4A. If you record a meeting, a lecture or an interview on an iPhone, you get an M4A.
A typical job
You record something on your iPhone and the person you send it to cannot open it. Converting to MP3 takes less than a minute and removes the compatibility problem.
Protected files are different
Songs from before iTunes dropped copy protection in 2009 may be locked, usually as .m4p, and cannot be converted. DRM-free iTunes files convert without trouble. Only convert audio you own or have permission to use.
Quality in practice
M4A and MP3 are both lossy. Converting adds one more round of compression, but for speech and everyday music it is difficult to hear. Keep the original if the recording is important.
Recording something important on your iPhone? Keep the original M4A as the backup, and send the MP3 for convenience.