sox --norm infile outfile

mp3gain -r *.mp3

mp3gain -c -r *.mp3

#!/bin/bash

find "$1" -iname "*.""$2" > $HOME/file_list

cat $HOME/file_list | while read line; do
#  echo "$line"
  orig_gain="$(normalize-mp3 -n "$line" | cut -d 'd' -f1)"
  larger=$(echo "$orig_gain"'>'-12 | bc)
  if [[ larger ]]
    then
      gain_difference=$(echo "$orig_gain"*-1-12 | bc)
    else
      gain_difference=$(echo "$orig_gain"-12 | bc)
  fi
  echo "Gain Difference will be: $gain_difference""db"
  normalize-ogg --mp3 --bitrate "$3" -g "$gain_difference""db" -v "$line"
done

normalize-mp3 <directory> <file extenstion(with no leading dot)> <bitrate>

replaygain --force *.mp3

#!/usr/bin/python
"""
Parallel normalize gains
"""

from subprocess import Popen, PIPE
from multiprocessing.dummy import Pool as ThreadPool
from os import listdir

def regain(target):
    '''regain'''
    proc = Popen(['normalize-ogg', '-n', target["name"]],
                 stdin=PIPE, stdout=PIPE, stderr=PIPE)
    output, err = proc.communicate()
    print output
    level  = output.split()[0]
    if "dBFS" in level:
        level = level.split("dBFS")[0]
    level = level.replace(',', '.')
    level = int(round(float(level)))
    delta = target["gain"] - level
    if delta is 0:
        return 0

    proc = Popen(['exiftool', target["name"]],
                 stdin=PIPE, stdout=PIPE, stderr=PIPE)
    output, err = proc.communicate()
    bitrate = '0'
    for line in output.split('n'):
        if 'Nominal Bitrate' in line:
            bitrate = line.split(':')[1].split()[0]
            break
    if bitrate is '0':
        return -1

    proc = Popen(['normalize-ogg', '--ogg', '--bitrate', bitrate,
                  '-g', str(delta) + 'db', target["name"]],
                 stdin=PIPE, stdout=PIPE, stderr=PIPE)
    output, err = proc.communicate()
    return proc.returncode

# function to be mapped over
def parallelregain(gain=12, threads=60):
    '''parallelregain'''
    pool = ThreadPool(threads)
    targets = []
    files_list = listdir(".")
    for filename in files_list:
        if filename.endswith("ogg"):
            target = {
                "name":filename,
                "gain":gain,
            }
            targets.append(target)
    pool.map(regain, targets)
    pool.close()
    pool.join()

if __name__ == "__main__":
    parallelregain(gain=-12, threads=10)