Producing Your Audiobook

Deeper Dives

Choose an Ideal Recording Space:

• Low noise floor (free from any internal or external sounds)
• Rectangular, with low ceilings and 90 degree corners
• Not too big (like a kitchen), or you'll get echoing, muddy sounds
• No hard, non-porous surfaces like mirrors and porcelain, which bounce sound harshly
• Soft room lighting (Avoid fluorescents or anything with a dimmer)

Make a "Dead Room" with Acoustic Treatment:

Eliminate echoes and reflection with absorption materials. Place curtains, rugs, foam, and other such materials on surfaces behind the microphone and on the side walls, at a distance exactly halfway between your sitting position and the microphone stand.
If you use a laptop to record, be aware of when the fan goes on - shut it off and let it cool for a while; if you use a desktop, you might keep the monitor and keyboard in the recording space, but keep the fan noise outside.

Check out these examples of ACX user recording spaces. Note they range from very simple to more complex:

Equipment Checklist

• A comfy, non-creaking chair
• Script stand
• Microphone (see below: large-diaphragm condenser mic preferable)
• Mic stand/mount
• Mic shock mount
• Pop filter
• Audio interface with pre-amp (pre-amps power the microphone; interface connects to your computer to record)
• XLR cable (connects microphone to audio interface)
• Fast and quiet computer
• External hard drive (always record your audio to an external HDD)
• Recording/editing software (aka Digital Audio Workstation, or DAW)

ALSO… Good headphones make an impact on every single aspect of audiobook production, from recording to mastering.  Check out this blog post that's all about headphones: Studio Gear Series (Part 3): Headphones

Setting Up Your Microphone

We recommend a large-diaphragm cardioid condenser microphone. They're typically more accurate than other types of microphones, but are also more sensitive to mistakes. These setup best practices can help you get the most out of your purchase:

• Placement: Choose a point no farther than 40% away from the front wall. Ideally, the microphone would be placed halfway between the side walls.

• Height: Microphones placed at or below mouth-level tend to pick up more "body" in a voice, while placement above the mouth (closer to the nasal cavity) captures a more "bright" and airy sound. Experiment with different configurations to hear what sounds best.
  
• Distance: Stand the microphone about 6-10 inches from your mouth. This should help you avoid plosives, but we strongly recommend purchasing a pop filter for your microphone if it doesn't already come with one. (For you DIYers, you can construct your own pop filter out of pantyhose and flex tubing, as demonstrated in this Lifehacker article.)

• Interface: All cardioid condenser microphones require an audio interface that can provide phantom power to the microphone. If phantom power is not provided to the microphone, then it will not work.

Additional Links

• ACX Studio Gear Series
• How to Succeed at Audiobook Production: Part 1
• ACX Studio Gear Series: Home Studio Setup: Part 1
• Home Studio Setup with Andrew the Audio Scientist : Part 1

Before you start production, listen to these examples of good, quality recordings. Open them in your recording software to not just hear, but see how they work:

Notice how quiet the room is. Also note the dynamics, how there is variation in the level of the narration, yet it doesn't swing between too loud or too quiet. This is the end result you want.

Below are examples of poor quality—high noise floor, distortion, phasing issues, etc.:

If you notice your production is starting to have one or more of these issues, take a step back, correct the issue, and restart the recording process.

Setting Your Levels (Gain Staging)

Gain staging is the process of having the strongest input signal while minimizing the noise inherent in audio recording. This occurs at every instance of the recording chain, from mic pre-amp to the track in the DAW. Good gain staging will maximize your input’s signal to noise ratio while having optimal headroom.

Having the correct amount of headroom along with good signal to noise ratio means your recording setup will allow the audio to be as loud and dynamic as possible without clipping as well as little noise during the quiet parts of the recording. This includes hissing noise, which usually appears when the gain is too high or part of the recording setup is faulty. Condenser microphones, while most preferred for audiobook recording, are very sensitive and more prone to this type of noise.

The ACX requirement for RMS is to have a recording between -23dB to -18dB RMS, with peaks hitting a max of -3dB. In your DAW of choice, arm the recording track so the input signal is visible on the track’s meter. Record test narration until your RMS is between the requirement’s range. While we allow a max of -3dB for peaks, it’d preferable to have -6dB to -9dB of headroom.

If you notice hissing noise, your pre-amp’s gain might be too high. In this case, you should lower your pre-amp while raising the input on the track in your DAW. It’s finding the balance that will give you optimal performance.

Recording Advice

• Draft a production schedule: An experienced ACX producer spends roughly six hours in production for every hour of completed audio. (Those new to the format often spend considerably more.) This means, for a five-hour title, you should anticipate spending at least 30 hours on production and completion.

• Perform a thorough script prep: Before recording, ensure you've read, notated, and fully understood every line of your script. Send questions unanswered by your script prep to your Rights Holder, and do your research. Sites like AudioEloquence.com are great for determining the accepted pronunciations of foreign, historical, and other uncommon words.

• Log your optimal settings: Once you've obtained a good microphone gain on your audio  interface and positioned your microphone perfectly, mark the area with electrical tape so you have a reference. This way, you'll be able to mimic your exact position and settings from day to day.

• Verify and record room tone: After setting your levels, record "room tone" at the start of every session. This is 15-30 seconds of air that you'll use during editing. Learn more about room tone—and hear more examples—in this ACX blog post.

• It's better to "punch" record mistakes: If you make a mistake while recording, it's better to stop and go back and re-record, rather than plow ahead with the corrected version, thinking you'll go back and edit out the mistake later.

• Read from a tablet: This is how professional narrators avoid sound from pages turning. Apps like iAnnotate let you mark inflections and such, like you would on a script. Just make sure any device sounds or notifications are turned off.

• If you use plugins: If your DAW allows you to record multiple versions simultaneously, one should be raw, and the other can be with plugins activated. If you have to choose between versions, it is much safer to record a raw version and apply plugins afterward.

• Always record to an external hard drive: Don't rely on your computer's hard drive—and save constantly!

• Back up your raw audio: Do this daily. We've outlined a secure system in our blog post on File Management.

• Give your audio files clear, explicit names. Include the recording date and chapter or section number and name.

Additional Links & Resources

• Putting Your Best Sound Forward
• Andi Arndt's Audiobook Agenda

Critical Listening

• Put on your headphones and listen to a few minutes of each section of your audiobook. By briefly taking in the overall sound and rhythm of the narration, you can better identify areas that stand out as distractions. 
• Turn up the volume so it's easier to detect noises that may become problems after mastering (the last step of production).

Editing

• Remove extraneous sounds from your recording (mouth noises, pops, keyboard clicks, etc.).
• Modify the pace of narration, if necessary.
• When appropriate, replace portions of the recording that you edited out with clean room tone.
• Divide the chapters into individual files, and prepare the spacing of their heads and tails to ACX's Audio Submission Requirements: 0.5-1 second at the head and 1-5 seconds at the tail.

QC

• Listen through the entire audiobook while reading the manuscript to ensure they match exactly.
• Mark down any errors (misreads, mispronunciations, or noises you can't edit out) to a QC sheet, which will be used when you rerecord. You can find the QC sheet Audible Studios editors use here.
• Re-record areas needing improvement and place these new recordings into the edited audio (sometimes called "pickups").

Mastering for ACX Requirements

When Audible releases an audiobook to the market, it has to work within a range of different audio formats employed by Audible, Amazon, and iTunes. This means that audio quality will range from very high fidelity to lesser fidelities that equate to smaller file sizes and quicker downloads.

Mastering Checklist

1. Import all your title's files together so they can be processed at the same time.
2. Check each file to ensure there is no clipping. A good recording and careful editing are both necessary to achieve this.
3. Bring each group of audio files into your digital audio workstation (DAW), and perform the following processes in this order (this is referred to as your "mastering chain"):

• Use an EQ to remove unnecessary low and high frequencies. The human ear can detect a frequency range from 20Hz (bass/low end) to 20,000 kHz (high end). Most EQ plug-ins have a high pass filter and a low pass filter. Using the high pass will remove unwanted low frequencies that could have occurred during recording, such as the hum of your computer. A low pass will remove high frequency noises in your audio, like an air conditioner or microphone hiss. Removing a low frequency hum allows you to better adjust narration levels.
• Use a limiter to bring down peaks. Peaks create distortion and may impede you from getting your audio levels within acceptable range. If you're starting out with any 0dB peaks, find out whether they occurred during recording or after. If it happened during recording, lower your pre-amp's level and re-record those lines of narration.
• Bring up the overall volume to meet ACX's RMS requirement (-18dB RMS to -23dB RMS). If your max peak level is -4dB but your overall RMS level is -27dB RMS, your audio will look like this (click images to expand):

In this case, use a limiter to lower all peaks by -3dB. Your max peak level is now   -7dB, which looks like this:

Since ACX's peaks requirement is -3dB, you can now raise the overall level of the audio by +4dB. That brings your RMS to -23dB RMS, which is within our required range. Your mastered audio now looks something like this:

1. Listen to your audio after mastering to ensure the operation did not over-process or under-process the recordings.

A Word Noise Gates

We don't recommend them. While a noise gate and even noise removal software could be helpful, if used incorrectly, it will heavily degrade the audio. If you have a section that is an hour or two long, one noise gate preset will not work for the entire section. If you put more time and resources into your home studio setup and recording techniques, you shouldn't need noise gating/removal.

Additional Links & Resources

• Alex the Audio Scientist - Mastering
• Alex the Audio Scientist - All About Noise Floor

Before You Begin

Before converting to MP3, back up your work! We highly recommend saving a "final" version of your audiobook before beginning the encoding process. It's best to archive your completed audiobook's contents as individual WAV files (broken up by section) with the following properties:

• Sampling rate: 44.1 kHz
• Bit depth (or bit rate): 16 bit
• A length of 120 minutes or less

Here’s the optimal way to back up your audiobook

1. Have a master folder that will contain all of your audiobook productions.
2. Create a folder for your audiobook in the master folder.
3. Export each section of your audiobook as a WAV, with the specs above, to this folder.
4. Name each file with its section number first, then the section name.
1. Ex: 00_Opening Credits.wav, 01_Introduction.wav, 02_Chapter-01.wav, etc.
5. After naming all the files this way:
1. Drop the exported WAVs into your DAW.
2. Look at the entire waveform of each file to make sure there are no accidental gaps or glitches.
3. Listen to the beginning of each file to ensure it has the correct credits and/or section header.
4. Listen to each file’s tail to ensure there’s proper spacing and no narration from the next section.
6. For safety, copy this folder and make a backup on an entirely different hard drive. This reduces the chance of losing your work in case one of the hard drives fails.

Encoding Your Audiobook

1. In your DAW, open the project with the section you wish to encode.
1. Most DAWs use the words “Export” and “Bounce” to refer to encoding.
2. Highlight the track and make sure it has the correct start and end range.
3. Go to your DAW's encoding menu.
4. Make sure your encoding is set to export as:
1. Constant Bit Rate MP3
2. Bitrate of 192, 256, or 360kbps
3. Check that all files are either mono or stereo (mono is recommended)
5. Set your encode/export/bounce directory to the folder you made for this production.
6. Encode the file.

Congratulations! Your audio files are now ready for submission.

Additional Links & Resources

• ACX 5-Part Blog Series: Why Didn't My Audiobook Pass QA?