AudioBook Technical Mastering with Audacity (rev 4)

AudioBook Technical Mastering - Revision 4 is available with custom software, changes and updates. It's available as of this writing on the Audacity Forum.


-- Legacy Version 1--

These are all technical considerations. Nothing here will address theatrical errors such as harsh sibilance, gritty voice or wet mouth noises.
The quality of the original recording is very important. It's easy to record mistakes that can't be fixed later. Record to a reasonable volume (occasional peaks at -6dB) in a quiet room with no echoes.
When you get done with a chapter, File > Export the work as WAV (Microsoft, 16-bit) and save the sound file with a unique name somewhere safe. That's your emergency backup so you don't have to read it again if you damage or lose your edit.
Only then start editing, processing, filtering and correcting. Keep testing the work with the add-on ACX Check analysis tool as you go. Select the work and Analyze > ACX Check.
ACX Technical limits:
— Peaks no louder than -3dB.
— Noise no louder than -60dB.
— RMS (performance loudness) between -18dB and -23dB.
Those are the top three values in the ACX Check panel
ACX Values in English
Human Quality Control at ACX (the theatrical test after you pass ACX-Check technical test) does not like heavy processing. You should be as gentle as you can with as few corrections as possible. Don't even think of submitting readings that sound like a bad cellphone or speaking into a wineglass.
Some readers may make it all the way through the last correction and fail to pass noise. Those performances may need to be custom processed by hand...or read again in a better room or with a quieter microphone or computer.
Also, some microphones have special noise problems. Record a short test clip and post it on the Audacity Forum.
There is also this noise note.

Get and install SetRMS and LF-Rolloff.
Get and install ACX Check.

Start this process with a raw, uncorrected reading, no processing or fixes. Don't help.
Apply SetRMS and Limiter.
Analyze > ACX Check
If you did a good job on the recording, you may be finished — out the door.
If noise fails by very little, you can go on to Noise Reduction .
Apply Noise Reduction
Drag-select Room Tone, silence or the flat area between spoken phrases.
Effect > Noise Reduction: Profile
Select the whole clip or show by clicking just above MUTE.
Effect > Noise Reduction: Settings 6, 6, 6 > OK
Analyze > ACX Check
Still not quite enough? Some microphones come out of the box with very low pitch rumble noise. There's a custom filter for that, but it comes with rules.
— Once LF-Rolloff is used, you have to use it on all chapters. It changes the voice just enough so the sound is not transparent. It is required the chapters match.
— If you have a nice low, rumbly broadcasting voice, forget it. This filter will destroy your voice.
Apply LF Rolloff (rumble filter)
Select the whole clip or show by clicking just above MUTE.
Effect > Equalization: LF Rolloff for speech, Filter Length about 5000 > OK
Analyze > ACX Check
This is the end. If you don't pass by now, you may need to post on the Audacity Forum for help.
It's possible to pass technical standards and still have high-pitch whine, buzz or whistling noises behind your voice. Those noises will not pass Human Quality Control, even though the show passes ACX-Check. The noises may not respond well to Audacity tools and can be very difficult to fix. It's best to ask for help on the forum.
There's a good chance we're going to ask you to post a short test voice clip so we're all listening to the same thing.
Sign up for an account and post for help. The forum is moderated so your message may not appear immediately. Just post once. The forum elves will find you.
ACX has their own help pages, tutorials and videos.