Mastering 101 for Audiobooks

Mastering is all about adding effects to create the final sound. Your DAW (Digital Audio Workstation) lets you record, edit, and mix audio, but it’s the plug-ins that run the effects useful in mastering.

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Mastering Crash Course

Now let’s talk about those compressors, equalizers, amplifiers, limiters and gates mentioned in the discussion of What is Mastering.

Mastering is all about adding effects to create the final sound. Your DAW (Digital Audio Workstation) lets you record, edit, and mix audio, but it’s the plug-ins that run the effects useful in mastering. A plug-in is a software component that adds a feature to a software program. Many plug-ins recreate effects that used to only be possible with analog devices- physical devices that connected to the recording chain. Now, lucky for us, you can access a plethora of (free) digital plug-ins via your DAW. 

Pro Audio Essentials from iZotope has excellent learning resources for beginners. I can’t say enough good things about iZotope’s website. It is a fantastic place for beginners to start learning audio basics, get introduced to EQ and compression, and practice listening. 

Now that you know a teeny tiny bit about mastering and that there are different plug-ins, let’s talk about some of the specific plug-ins you will likely use in audiobook production. The series of plug-ins applied to your audio is called an effects chain, or a mastering chain. Start by reading Why Plug-In Order (Mostly) Doesn’t Matter. Or you can read what ACX has to say about the mastering chain, here.

Tip: Before you apply any effects, save this version under a new name. That way, if you’re tired after a long mastering session, you won’t accidentally save over and lose your raw/edited copy.

Mastering Chain for Audiobook Narration

The series of plug-ins applied to your audio is called an effects chain, or a mastering chain. The mastering chain I recommend for narration work is: 

Please Note: Just because an effect is on the list, does not mean you must use it. It is there to inform you as to where you would want to use it, when appropriate. 

Tip: If you have a long reading session, and record multiple chapters into one track, master that one track as a whole. Then, when finished mastering, split each section into their own file. It will provide a more consistent result – and be less work for you.  

0. Optional Saturation

Think of saturation like introducing harmonics. It emulates the sound and adds a bit of distortion. For narration, it can make recordings seem warmer and evokes a classic sound, like old radio broadcasters. It is not usually necessary for audiobook narration, but it’s listed here so, if you so choose, you know where in the effects chain to use it.

1. Equalizer: High Pass Filter (Low Rolloff for Speech)

Equalizers are often abbreviated as EQs. They attenuate (cut/reduce) or boost certain frequencies or ranges of frequencies. Applying EQs to attenuate undesired audio, and as a result, make the narration (or other element, like guitars in music) stand out is called Cleaning EQ. A filter is a type of equalizer.

A high pass filter attenuates signals lower than a set frequency, while letting the other (higher) frequencies pass by unaffected. The result is less rumble and other unwanted low frequencies, like some types of microphone noise. Slightly different types of high pass filters may be called a rumble filter or a line curve EQ. 

There are many high pass filters, with similar sounding names. For example a rumble filter and a low rolloff filter are basically the same thing with slightly different settings. All filters let you adjust the settings, but the right one for your voice and project is something you have to find out for yourself (or hire an engineer to do for you). 

Low Rolloff filters are an excellent choice for narration. Especially if they have a “low rolloff for speech” preset option. For example, in Audacity go to Effects > Filter Curve EQ > Manage > Factory Presets > Low rolloff for speech. 

Whatever filter you decide to use, you want to apply it early, if not first, in your effects chain. Why? So you have less of the noise you don’t want for the rest of the project. 

EQ Learning Resources

Review of Frequencies and Types of EQ

EQ Introduction 

Low Rolloff for Speech Video Tutorial (for Audacity)

2. Equalizer: Noise Reduction

The noise reduction plug-in is a targeted high pass filter to reduce room tone. It uses a selection of audio, a noise profile you select, to attenuate specific sections in the audio that match that profile. It is a great tool to reduce the room tone between the narration.

  1. After recording and editing, you should have at least 20-30 seconds of room tone at the beginning of your track. Clean up as much of your room noise as you can by cutting out the loudest parts. It may be helpful to look at the spectrogram to really get rid of extraneous frequencies. 
  2. Manually replace as much poor quality room tone, audible breaths, and so on with a copy of that clean room tone. But don’t go crazy trying to make it all perfect by cutting and pasting- that is why there are plug-ins- so you don’t lose your mind in this step. 
  3. Select your tidied up room tone for the Noise Profile/Noise Print/whatever it’s called by your DAW. 
  4. Now select a section of audio, or track, to apply the noise reduction filter to. 
  5. Trim out that extra room tone at the beginning and end, because you won’t need it any more. 

Noise Reduction Learning Resources

What is Audio Noise and Room Tone?

Noise Reduction Video Tutorial (for Audacity)

Noise Reduction Video Tutorial (for Adobe Audition)

Tip: Record a “Clean Room Tone” file. Have a minute or two of ultra clean room tone. That way, if you ever need it, you will have it one hand and can upload it into any noisy tracks.

3. Loudness Normalization -or- Peak Normalization 

Normalization and Loudness Normalization are, as they say, same same but different. 

  • Loudness normalization adjusts the average amplitude up or down to meet a set level. It measures audio amplitude AND space between audio (room tone), then boosts or attenuates based on the overall average. Relative dynamics will likely change as a result. Loudness normalization is most often measured in LUFS or RMS. 
  • Peak Normalization finds the peak (maximum) amplitude and adjusts it up or down to a set level. It finds the single highest point of amplitude and boosts/attenuates it to that new set level. Everything is adjusted by a constant value so the recording retains its relative dynamics. Peak normalization may also be referred to simply as “normalization.” 

Both are very helpful for providing a consistent amplitude level among various tracks recorded over various days. For voice over and narration, loudness normalization is recommended over peak normalization. 

If you are mastering to meet certain requirements (such as those of ACX), this step lets you set: 

  • RMS/LUFS level – via Loudness Normalization. ACX requirement: between -23dB and -18dB RMS. 
  • Peak dB values – via Peak Normalization.  ACX Requirement: -3dB.


Loudness Normalization Learning Resources

Normalization Video

Normalization Wiki

Normalization Video Tutorial (for Audacity)


4. Limiter -or- Compressor

A limiter and a compressor are different tools that both, you guessed it, affect amplitude. 

  • Limiter: A limiter sets an amplitude threshold (a ceiling) above which signals are attenuated. It is notably different from peak normalization in that it does not change the entire track, but only affects the audio that crosses above the threshold. A limiter is recommended for audiobook productions because it maintains the original dynamics while removing some of the loudest parts, those that would seem inconsistent to listeners. 
  • Compressor: A compressor adjusts the dynamic range of a recording. It makes the loudest parts softer and the softest parts louder. What that means is it moves everything towards the average. So if there is a sudden exclamation in the narration, it doesn’t leave your ears bleeding. And likewise, if something is whispered, it gets a boost so you can still hear it. On rare occasions, compression may be appropriate for narratives that have lots of significant highs or lows. 

The goal of limiters and compressors is to provide a more consistent amplitude (volume) throughout the audio experience- so that listeners don’t have to continually toggle the volume up or down to listen comfortably. While a limiter is generally recommended for voice over, it is not an absolute rule, and you will have to find the approach that works best for you. 

If you are mastering to meet certain requirements (such as those of ACX), this step lets you set: 

  • Peak dB values – via the Limiter. ACX Requirement: -3dB.
  • Consistent amplitude levels among audio files. 


Limiter and Compressor Learning Resources

Limiter v Compressor Video

Another Brief Limiter v Compressor Video

Limiters Explained Video Tutorial

Limiter Video Tutorial (for Audacity)

Limiter Video Tutorial (for Audio Pro X)

Limiter Video Tutorial (for iZotope Ozone)

Compression Video Tutorial (for Audacity)

Compressor Video Librar

5. Additive EQ: Amplify

If you still want to increase certain frequencies that didn’t come through enough in the previous steps, now is when you do that. Additive EQs boost, rather than attenuate, certain frequencies.

But be wary, it is better to attenuate unwanted frequencies rather than boost those you wish to highlight, because it is easy to distort the audio, or make it sound weird, by boosting. So only use additive EQ if it’s appropriate. 

Amplify is a common additive EQ. If a section, word, or phrase is still at an unwanted amplitude, amplify lets you boost (or attenuate*) by a set amount of dB. Or it can set a peak amplitude for that section. It lets you fine tune sections of your audio. It should be applied only if and where needed, not to the entire track. 

*Amplify can also attenuate selections of audio. So if something still has more amplitude than you want, you can apply a negative -dB gain (attenuate) to it by using amplify. 

Additive EQ Learning Resources

Additive v Subtractive EQ

Amplify Video Tutorial (for Audacity)

6. Noise Gate

A noise gate is a specific type of filter (yet another EQ effect). It can be helpful for removing any remaining background noise that still remains on your track, such as traffic or the sound of deep breaths. It reduces the noise between the actual narration, music, or whatever, by affecting frequencies below a certain frequency threshold. Noise gates let you set various parameters, but maxing it out so there is absolut silence in the track is not recommended because it makes the audio sound unnatural or computerized. For example, ACX has a maximum noise floor requirement of -60dB.

A noise gate is triggered by a threshold, so it is important to run the noise gate after other EQ, limiting, or compression effects. Otherwise the application could be inconsistent. 

Noise Gate Learning Resources

Noise gate

Noise Gate Video Tutorial (for Audacity)

Noise Gate Video Tutorial for Loud Breaths (for Audacity)

Another Noise Gate Video Tutorial

7. De-Esser

The de-esser is a useful tool for reducing sibilance. But be careful not to overdo it or the recording could get muddy. 

Like a noise gate, the de-esser is triggered by a threshold, so run it after other effects. Running it after the noise gate, rather than before, makes sure that any attenuation that happens here, isn’t accidentally cut out by the noise gate. 

To use a de-esser more effectively, determine at what frequency (measured in Hz) sibilance happens for your voice. For example, my sibilance seems strongest around 7200 Hz. 

De-Esser Learning Resources

Problem Frequencies Video

De-Essers Explained

Find the frequency of your sibilance (for Audacity)

De-Esser Video Tutorial (for Audacity)

De-Esser Video (for Adobe Audition)

Link to a free De-Esser plug in (.ny file type)

8. De-Clicker

Clicks are those unwanted mouth noises that happen when speaking, such as parting or smacking lips. But clicks can also appear from the editing process. A de-clicker helps to remove them. 

Like other plug-ins mentioned, the de-clicker is triggered by a threshold. As such, it should be one of the last plug-ins run. I prefer to run it near the very end of the chain, so if any clicks were accidentally created by other effects, this will catch them. 

The de-clicker runs best in focused sections of audio, meaning you may have to manually listen to the track and apply the de-clicker wherever you find a click. Doing it manually is more work, but makes sure any hard “d”, “t”, or other consonants aren’t removed by mistake. 

De-Clicker Learning Resources

De-Clicker Video Tutorial (for Audacity)

Another De-Clicker Video Tutorial (for Audacity)

Link to a free De-Clicker plug-in (.ny file type)

9. Optional Quality Check

There are various plug-ins tailored to checking your audio track to see if it meets certain parameters. For example, if you are using Audacity, you can download a free ACX Check Plug-in to double check your work (here is a link for how to install plugins) to see if it meets the specific upload requirements for ACX. 

QC Learning Resources

ACX Check Video Tutorial (for Audacity)

Other Plug-In Effects

There are other plug-ins you can use, when necessary, at any time throughout this process- because they do targeted fixes rather than large, comprehensive changes.

Fade Video Tutorial (for Audacity)

Envelope (for Audacity)

The list is too massive to do a review of them all.

Mastering 101
Mastering Chain 75%

Disclosure: This post may contain affiliate links, meaning at no additional cost to you, I will earn a commission or compensation if you click through and/or make a purchase. The opinions and recommendations expressed here are my own. 

Still Curious? Keep Reading

The music is not in the notes, but in the silence between.

― Wolfgang Amadeus Mozart

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