philologist's techblog

m4a to wav:

ffmpeg -i audiofile.m4a audiofile.wav

MP3 to WAV:
user@pc:~$ sox -t mp3 fromfile.mp3 -t wav -r 8k tofile.wav channels 1
user@pc:~/Downloads$ file tofile.wav
tofile.wav: RIFF (little-endian) data, WAVE audio, Microsoft PCM, 16 bit, mono 8000 Hz

or using mpg321:

mpg321 -w output.wav input.mp3

GSM to WAV:
lexus@lexus:~$ sox beep2.gsm -r 8000 --encoding=signed-integer beep2.wav channels 2
lexus@lexus:~$ file beep2.wav
beep2.wav: RIFF (little-endian) data, WAVE audio, Microsoft PCM, 16 bit, stereo 8000 Hz

OGG to WAV:
lexus@lexus:~$ ffmpeg -i in_file.ogg out_file.wav

Change WAV file bitrate from 44100 to 8000:
lexus@lexus:~$ file file44100.wav
file44100.wav: RIFF (little-endian) data, WAVE audio, Microsoft PCM, 16 bit, stereo 44100 Hz
lexus@lexus:~$ sox file44100.wav -r 8000 file8000.wav
sox WARN rate: rate clipped 12 samples; decrease volume?
sox WARN dither: dither clipped 8 samples; decrease volume?

For newer versions of sox, working example:

stereo to mono:
sox stereo.wav mono.wav channels 1

44100 t0 8000:
sox big.wav small.wav rate 8000