mpg123 is simple comman line tool to convert an MP3 to WAV, more info on

It easy to convert an MP3 to WAV from Linux command line,

mpg123 -w output.wav input.mp3

8-bit wav format

Buy default the ouput 16bit wav format, Here is how you convert to 8bit wav file

mpg123 --wav out.wav --8bit --rate 8000 --mono input.mp3