soxで全部の音をノーマライズ ref: http://qiita.com/asus4/items/0540445362e7eef3491f

normalize.zsh

#!/bin/zsh

# NEED sox
# brew install sox

EXPORT_DIR=normalized

# input folder
function mkdir_ex() {
    # create folder
    if [ ! -d $1 ]
    then
        mkdir $1
    fi
}
# normalize
function normalize() {
  sox $1 $EXPORT_DIR/$1 norm -1
}

mkdir_ex $EXPORT_DIR

while [ "$1" != "" ]
do
  normalize $1
  shift
done

SOX normalize

brew install sox

usage.zsh

./normalize.zsh *.aif