How to improve the sound quality of low quality audiobooks

Some of the Audiobooks found on the internet can be fairly low-quality. This will greatly improve the quality of some of those file.

Requirement

 * SoX - http://sox.sourceforge.net

Features

 * Processes all mp3's in a folder
 * Filters out frequencies below 400Hz and 2kHz
 * Normalizes audio
 * Reduces file size of over-sized mp3s
 * MP3 Quality: 64kbs, 1 Channel, 22050Hz bandwidth

Command

 * sox -S INPUT_FILE.mp3 -b 16 -c 1 -C 64 OUTPUT_FILE.mp3" bandpass 1200 1600h rate 22050 norm

Script
This script will make a directory "mod" and put the modified files in that directory


 * mkdir mod;for mp3 in $(ls -1 --color=none *.mp3); do sox -S "${mp3}" -b 16 -c 1 -C 64 "mod/${mp3}_mod.mp3" bandpass 1200 1600h rate 22050 norm; done

on my system i made an alias
 * alias audiobook_improve_voice='mkdir mod;for mp3 in $(ls -1 --color=none *.mp3); do sox -S "${mp3}" -b 16 -c 1 -C 64 "mod/${mp3}_mod.mp3" bandpass 1200 1600h rate 22050 norm; done'