Andrew the Audio Scientist here, and today I’m presenting part three of my How to Succeed at Audiobook Production series. Let’s dig into one of the most important, yet least understood aspects of audiobook production: Mastering. But before we tackle that, make sure you’ve done proper editing and QC passes on your raw audio. Check out last week’s post for more on those important steps, and read on for my advice on audiobook mastering.
Before we get to the video below, I want to remind you of the key to producing reliably great sounding audiobooks, especially in the mastering stage: consistency.
Mastering is, in essence, the process of bringing your files closer to one another in terms of sound quality and dynamic range, so the listener will enjoy a book which sounds the same all the way through.
The most important thing to remember about mastering is that it is done not to make a poor recording sound good, but rather to make a good recording sound great. Mastering, like editing, is a key aspect of the perceived professionalism of your production. While the average customer is not thinking about the mastering of a title while listening, the boost of clarity and consistency your narration receives from a proper master cannot be ignored. So, while the process of mastering an audiobook may appear cryptic at first, it is essential to achieving an optimal sound quality for your production.
Audiobook mastering involves a few major steps:
- Assess all audio files to ensure no peaks or clipping exist in the audio. A good recording and careful editing are both necessary to achieve this.
- Group all similar files together during the assessment so they can be processed at the same time.
- Bring each group of audio files into your DAW, and perform the following processes in the following order (this is referred to as your “mastering chain”):
- Remove all unnecessary low and high frequencies to clean up the sound of your recordings and provide more headroom in order to boost your files levels effectively. This is a great way to minimize hum and hiss in an otherwise good recording!
- Bring all files up to the proper dynamic levels as specified by the ACX Audio Submission Requirements page by using normalization, compression and/or limiting, and, if necessary, a final volume adjustment.
- Check the audio after mastering to ensure the operation did not over-process or under-process the recordings.
A common mastering chain for an ACX production is as follows:
Remove low (80hz and lower) and high (16kHz and higher) frequencies by using a high-pass and low-pass filter, respectively. Set the high-pass filter to remove sounds below 80hz, and set the low-pass filter to remove sounds above 16kHz. If available, set the Q to the highest-possible setting for both filters. Usually, that setting is 24dB or 48dB per octave.
Typically, you should normalize your peaks to -6dB.
We recommend using a limiter, if available, instead of a compressor. Compression can achieve similar results, but it may also decrease the dynamic range of your vocal recording if used improperly. To properly utilize limiting on your files, start by setting your limiter’s maximum output to -3dB. Then, turn up the gain on your limiter until you have achieved a loud, clear, and consistent sound. Don’t boost the level too high. Otherwise, you may distort your voice, or bring up the noise floor of your recording too much. Remember: the better your recording and editing, the easier this process will be! If you have not yet read the first and second parts of this blog post series, I strongly recommend you do so. It can greatly reduce the workload involved in mastering your audiobook.
Tips for Each Step of the Mastering Process
Before you begin mastering, record and edit the entire audiobook to completion. Then, make a final “completed edits backup,” – which I refer to in my prior blog post on file management – of each chapter. Maintaining a backup file is imperative, in case you discover any issues with the audio while mastering.
A good recording is everything. Prior to mastering, a well-recorded audio file will have an RMS value no greater than -28dB RMS and peaks at a level no higher than -12 dB This provides the headroom needed to boost the volume of your production without needing to compress the signal heavily. If your peaks are already nearing -3dB before mastering, make sure no loud noises remain in the audio. If no erroneous sounds are found, then it’s likely you recorded too loudly. This is why learning how to properly prepare for and record your narration is essential to performing a successful master.
Plugins cannot help an inconsistent or noisy recording. Some people attempt to fix deficiencies in their recordings or their editing by using noise reduction plugins and gates. Software like this can be effective if used properly, but more often than not, the use of such plugins will cause more harm than good on an audiobook production. I strongly recommended you take the time to focus on your recording environment, as well as your recording and editing techniques, so you do not need to resort to the use of such software. It will save you valuable time as well as money – those plugins can get expensive!
In order to group your audio files together effectively, leverage the audio measurement tools available in your DAW to find the audio files that are similar to one another. If you are an Audacity user, the “stats.ny” plugin will be essential to performing this task. See this thread from the Audacity forums for installation and use instructions.
Most DAWs have a similar capability, so if you are not aware of what tools can be used to achieve these actions in your particular software, contact the manufacturer to receive assistance in their use.
Double-check your masters. Use the same function on your DAW that you used to group your pre-mastered files in order to check your new mastered files. If your audio measurements fall within the ACX Audio Submission Requirements, you should be good to go, which brings us to our final step.
Verify the following ACX Audio Submission Requirements. Are all of your files’ peaks hitting around -3dB? Is each file’s average RMS between -18 and -23dB RMS? How audible is your noise floor at normal listening levels? There’s no shame in attempting a second master if you’ve found flaws in your new mastered files – that’s why you saved your Completed Edits Backup files after you completed your edits.
In truth, the most important mastering tip I can impart upon you, is to try, try again until you get it right! Mastering is very much a process of trial and error until you learn the tips and tricks that suit your production environment. Once you find settings for your mastering chain that work well for your voice and recording space, remember to save the configurations as presets so that you can easily reference them for your next ACX title. If you’ve established a consistent workflow for the recording and editing stages of audiobook production, then your mastering workflow will be a piece of cake!
Do you have mastering tips that Andrew didn’t cover here? Share them in the comments below, and join us next week for the fourth and final part of Andrew’s series: encoding and file delivery.