Convert a .mp3 to wav file with mplayer
ffmpeg should do the job. This line will convert to 8kHz 1 channel wav file.
ffmpeg -i input.mp3 -ar 8000 -ac 1 output.wav
http://ffmpeg.org/ffmpeg-doc.html#SEC11
I'm not sure about the 8 bits requirement - what are you referring to? It's not the bitrate surely?
lame, the command-line WAV to MP3 encoder, can also decode MP3 to WAV with the --decode switch.