On 02 Apr 2019, "J. P. Gilliver (John)" wrote
in alt.windows7.general:

Since the editor I use doesn't accept .m4a, I use Pazera's
"extract to WAV" function, and proceed from there.

You might want to look at the free Audacity editor, which can open and
save M4A format. It's not my daily audio editor (Adobe Audition is),
but it's got a good feature set, is in active development, an active
support base, and you can't beat the price.