How to edit audiobooks [Plus Useful Apps List]

_{Update December 09: Added MediaInfo to Useful tools (tip by Dallis24)}
_{Update December 09: Added MP3Gain and EncSpot to Useful tools (tip by Horstman)}

Purpose
The purpose of this tutorial is to describe how to use various tools to edit audiobooks.
The most common reasons I have to edit audiobooks are to remove noise, normalize sound level, split/cut into chapters or join multiple parts into one file.

Remove noise with Audacity

Why
The audiobook has constant background sounds such as hum, whistle, whine, buzz and hiss (such as tape hiss or fan noise).

PS! If the noise is mains hum or a high-pitched whistle, try Notch Filter before applying Noise Reduction.

How

Open Audacity
Click menu File > Import > Audio
Select and import the audio
Click menu Select > All (If multiple tracks)
Click menu Tracks > Align Tracks > Align End to End (If multiple tracks)
Zoom in and select a part that contains only the noise you want to reduce
Click menu Effect > Noise Reduction > Get Noise Profile
Click menu Select > All (or select only the part where you want to reduce noise)
Click menu Effect > Noise Reduction > edit parameters > Preview
Once satisfied click OK in Noise Reduction to remove the noise
Click menu File > Export > Export as MP3 (or use Export multiple if you have multiple tracks and want one file for each track)

Sometimes you may want to remove sound that noise reduction cannot remove:

Select the part that should be silent.
Press space to listen to it, you do not want to remove sound that should be there.
Press space again to stop playing.
You can adjust selection by holding down Shift and use arrows left and right and/or click with the mouse.
When the selection is correct, press Ctrl+L to Silence Audio.
Click menu File > Export > Export as MP3 (or use Export multiple if you have multiple tracks and want one file for each track)

To see another guide about this look at Reducing background noise with Audacity.

PS! Audacity can use a lot of disk space, to free up space while working on a project you can use View > History to discard undo levels and reclaim disk space.

Normalize sound level

Why
The sound level is to high or to low or sound level varies in the audiobook.

How with mp3DirectCut

mp3DirectCut can normalize the sound level without reencoding the file. This is useful if you do not need to edit the audio because the sound quality is good and the sound level do not vary within the file.

Open mp3DirectCut
Click menu File > Open
Select the audio file
Click menu Edit > Normalize
Adjust the dB level, for audiobooks it is a good practice to normalize at -6 dB
Click OK to apply the change
Click menu File > Save complete audio
Save the file with a new name

How with Audacity

If the sound level varies within one file, you can use Audacity to normalize selected parts of the file separately. This is needed because if you normalize the entire file, the parts that are to low or to high relative to the other parts will still be to low or to high after normalizing.

Enable or add RMS-Normalize plug-in
Open Audacity
Click menu File > Import > Audio
Select and import the audio
Select up to one hour of audio
Click menu Effect > RMS Normalize: Target RMS Level -20dB > OK
Click menu Effect > Limiter: Soft Limit, 0, 0, -3.5dB, 10, No > OK
Repeat step 5 to 7 for the rest of the audio until all is normalized
Click menu File > Export > Export as MP3 (or use Export multiple if you have multiple tracks and want one file for each track)

PS! You can use Macros to automate the three tasks above (RMS Normalize, Limiter and Export as MP3).

Read more in AudioBook Mastering version 4.

Split/cut into chapters

You can use mp3DirectCut to split the file without reencoding it. You can also import audio in Audacity and split it into separate tracks but this will require reencoding.

How with mp3DirectCut
Chapterizing books -- splitting MP3s by chapter.

How with Audacity

Open Audacity
Click menu File > Import > Audio
Select and import the audio
Click menu Select > All (If multiple tracks)
Click menu Tracks > Align Tracks > Align End to End (If multiple tracks)
Click menu Tracks > Add new > Mono track (or Stereo track). This is where you will paste inn the next chapter.
Zoom in until you see something that looks like silence before a chapter.
Click to set the Cursor before chapter starts.
Press space to start playing and verify that you have the correct possition before chapter starts.
Press space again to stop playing.
Ensure that the Cursor starts where there is no sound.
Ensure that project rate (Hz) and track rate is the same.
Press Shift+K to select from Cursor to Track End.
Press Ctrl+Alt+X to Split Cut the sound.
Press Enter to deselect focused track.
Use arrow key to move to the empty track where you will past inn the next chapter.
Press Enter to select focused track.
Press Ctrl+V to paste inn the next chapter.
Repeat step 5 to 17 for all remaining chapters.

Sometimes you may want to add silence between chapters:

Click where silence should be added
Click menu Generate > Silence
Click menu Select > All
Click menu Tracks > Align Tracks > Align End to End

Sometimes you may want to remove some of the silence between chapters or remove other parts of the sound:

Select the part that should be removed.
Press space to listen to it, you do not want to remove sound that should be there.
Press space again to stop playing.
Press Delete.
Click menu Select > All
Click menu Tracks > Align Tracks > Align End to End

PS! You can assign a keyboard shortcut to any command in the menus.
E.g. Add new mono track: Ctrl+I, Move Focused Track Down: Ctrl+G, Move Focused Track Up: Ctrl+H

Join parts into one file

You can use mp3DirectCut to join the files without reencoding it.

How with mp3DirectCut
Chapterizing books -- splitting MP3s by chapter.

Fix mp3 files
See How to Fix wrong duration in MP3s (MP3 Playback/Conversion Issues).

Useful tools

Name	Description
Audacity	Tool to edit audio, many plug-ins exist
mp3DirectCut	Tool to cut mp3 (and aac) files without reencoding the file
Mp3Tag	Tool to edit tags of audio files
MP3val	Tool to scan and fix mp3 audio files that has commonly known issues
MediaHuman Audio Converter	Tool to convert audio with gui
FFmpeg	Tool to convert audio and video from command line
inAudible	Tool to decrypt and convert audiobooks from Audible
M4ACut	Tool to split m4a/m4b files by chapter (if the file has chapters) or by specified duration
Spek	Acoustic Spectrum Analyser
VLC	Can play video and audio and will also show chapters in audiobooks
MusicBee	Very nice music manager and player, even for audiobooks
Notepad++	Good text editor, useful when editing metadata files exported with ffmpeg
MediaInfo	To view source file info, including the list of chapter times and titles for m4b (tip by Dallis24)
MP3Gain	While Mp3directcut can adjust the level per file, this one can normalize individual files or whole folders and detects and warns of clipping. (tip by Horstman)
EncSpot	To view encoders and bitrates. Allows to see a list for whole folders (and calculates the average bitrate too). (tip by Horstman)

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