M4A is a weird format, so you have to be creative here is a quick copy of what I did. 

Basically you need to convert to .wav to make use of them and then I converted the resulting .wav into an mp3 (nice small file size and basically universally playable):

=======

sudo apt-get install mpg321 mp3gain faad normalize lame

 faad "Voice 002 (copy).m4a"

faad "Voice 002 (copy).m4a"
 *********** Ahead Software MPEG-4 AAC Decoder V2.7 ******************

 Build: May  1 2012
 Copyright 2002-2004: Ahead Software AG
 http://www.audiocoding.com
 Floating point version

 This program is free software; you can redistribute it and/or modify
 it under the terms of the GNU General Public License.

 **************************************************************************

Voice 002 (copy).m4a file info:

LC AAC    4107.565 secs, 2 ch, 44100 Hz


normalize-audio "Voice 002 (copy).wav"
Computing levels...
 Voice 002 (copy). 100% done, ETA 00:00:00 (batch 100% done, ETA 00:00:00)
Applying adjustment of 6.22dB to Voice 002 (copy).wav...
 Voice 002 (copy). 100% done, ETA 00:00:00 (batch 100% done, ETA 00:00:00)

  ---------------------
 | Config:  2 Ch       |
  ---------------------
 | Ch |    Position    |
  ---------------------
 | 00 | Left front     |
 | 01 | Right front    |
  ---------------------

Decoding Voice 002 (copy).m4a took: 45.95 sec. 89.39x real-time.



# not loud enough?
#run again with the -g parameter and the manual decibel increase
normalize-audio -g 20 "Voice 002 (copy).wav"

#convert to mp3

lame "Voice 002 (copy).wav"

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