Ручками

 #!/bin/bash

  echo "** THIS SCRIPT REQUIRES LAME AND SOX TO WORK!**"


  #Convert mp3 files to wav

  for i in *.mp3; do

  val=${i%.mp3}

  echo  "** Converting mp3 to wav files if they exist"

  lame --decode "$i" "$val.wav"

  rm -f "$i"

  echo "** $i MP3 to WAV is complete"

  done


  #Convert wav files

  for i in *.wav; do

  val=${i%.wav}

  echo "** Checking volume levels for $i"

  ampl=`sox "$i" -t wav /dev/null stat -v 2>&1 | grep -v sox:`

  echo "** Amplifying volume by $ampl to fake a normalize and converting $val.wav to 16 bit 8000"

  sox -v "$ampl" "$i" -t wav -r 8000 -c 1 -w -s "$val.converted.wav" resample

  rm -f "$val.wav"

  echo "** Reducing the volume"

  sox -v .5 "$val.converted.wav" "$val.wav"

  rm -f "$val.converted.wav"

  echo "** $i is complete"

  done

whereis sox

Выведет

sox: /usr/bin/sox

Если нет - yum install sox

Скрипт называеш, например, convert.sh

chmod 777 convert.sh

И кладеш мп3 в папку со скриптом.