How to Normalize and Increase the Volume on M4A files in Linux
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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