Welcome, students! For my first lesson of the new year, I’ll be focusing on a key piece of equipment in your studio – your microphone. The video below is chock full of helpful info, but before we get to that I want to give a quick shout-out to J.L. Rebeor, who was first to comment with all of the correct answers to my quiz last fall. You can check out her ACX profile here. Congrats, J.L.!
Now, on to the lesson. And be sure to stick around for today’s quiz, as I’ll once again honor the first commenter to earn a 100% in my next post.
Pencils down! It’s time for our quiz. Leave your answers in the comments below for a chance at a mention in a future blog post.
A microphone’s polar pattern indicates _______.
What are the three basic polar patterns a microphone can have?
What polar pattern is preferred for audiobook recording?
If your microphone is positioned too close to your mouth, you may end up with excessive _______ and _______ in your recording.
We’re less than three weeks away from this year’s December 4th deadline to submit your audiobook productions for the best chance of being on sale this holiday season.
With that in mind, today’s lesson is about the file submission process. Being so close to the goal can lead to tunnel vision, but following the steps below, along with my other lessons, will ensure that you don’t stumble at the finish line.
To set yourself up for success when submitting your finished audio, I suggest the following:
Export your entire audiobook to its own folder.
Name each file with its section number first, then the section name.
Ex: 00_Opening Credits, 01_Introduction, 02_Chapter-01, 03__Chapter-02, etc.
Stick to alphanumeric characters, dashes, and underscores. File names with other characters might cause upload issues on ACX.
After using this file naming convention, you should:
Drop all of your files into your audio player of choice (Winamp, VLC, iTunes, etc.)
Listen to the beginning of each file to ensure it has the correct credits and/or section header.
Listen to the end of each file to ensure it includes proper spacing and contains no narration from the next section.
Now that we’ve covered best practices, let’s look at some common issues that cause productions to be returned to the producer by our QA team, and how to rectify them.
Your ACX audiobooks should match the text editions exactly, without repeated sections. Duplicate audio can happen for a few main reasons:
Part of a chapter/section is repeated in another section.
For example, an audiobook production contains opening credits at the start of both the first and second file. To avoid this, make sure each audio chapter/section matches the text exactly during the Edit/QC process. I also recommend checking the head and tail of each file after editing and mastering your audiobook to make sure they don’t contain duplicated audio, and to confirm that each starts with a section header and ends with the last sentence of that section.
A chapter/section is named properly, but uploaded twice to the production manager.
Consider a checklist for your production that lists all of the files, and checking off each file when it’s uploaded.
A chapter or section is named improperly, resulting in duplicate uploads with different file names.
This third issue occurs during the exporting process, when you output each chapter or section from your DAW as an MP3. Before you export each chapter/section, double-check that you are exporting the correct one. If you’ve got multiple sections in one project file, don’t forget to isolate the correct section for export, and be sure to select the next section after exporting the previous.
My favorite solution is to create a separate project/session file for each chapter/section within your DAW of choice. If you have a work folder that contains a project file for each section, your workflow will be smoother and easier when accessing/re-accessing an audiobook’s production. Having a separate project file for each section all but guarantees a section will be exported as two separate files.
Listening to an audiobook in the Audible app.
This is when two or more entire sections are combined into one file. ACX’s Audio Submission Requirements state: Each uploaded file must contain only one chapter or section. This requirement is in place for the sake of the listening experience. Navigation within an audiobook should be simple. If chapters one and two are combined in the same file, the listener won’t be able to skip to the latter on their device; they would be forced to navigate manually through one file in hopes of finding it.
This can also be solved during the export process. As I noted previously, creating a separate project/session file for each chapter/section will ensure you’re not combining two separate pieces of audio.
The retail audio sample for each audiobook has a great deal of influence on the purchasing decisions of Audible’s listeners. They should be instantly captivated by the performance and impressed with the production. Work with your Rights Holder to select a portion that highlights your performance and their storytelling. ACX’s requirements call for “a retail audio sample that is between one and five minutes long.”
A red box highlights Huntress Moon’s retail audio sample.
Additionally, I strongly advise against including opening credits and/or music in your sample. This content is secondary to your actual performance, and potential listeners may not make it through to hear your narration.
Finally, make sure the sample includes no explicit language or material, as listeners of every age and sensibility can preview samples on Audible.
That’s today’s lesson. Following each of the tips above should result in a seamless upload and submission process, which means fewer headaches for you, your Rights Holder, and your potential listeners.
Today’s lesson is going to be a little different from my others. Since I’m lucky enough to have such eager students, I often get questions about one of the more mystifying aspects of audiobook production: mastering. Today, I’ll answer the most common questions and give you a breakdown of the basics steps of the mastering process. But first, let’s review ACX’s Audio Submission Requirements:
Now that we’ve covered the basics, let’s get to those questions.
Q: Why do I need to master my audiobook productions?
A: Mastering is the the final step of post-production and the glue that brings the entire audiobook together. All chapters/sections are brought up to matching levels, which provides a smooth listening experience. Additionally, removing unwanted high and low frequencies can help reduce any hum or hiss that may be in a recording.
Q: Why do I need to follow all of these mastering requirements?
A: Audible offers each audiobook in a range of different audio formats to accommodate listeners on 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. Basically, if your RMS is between -18dB and -23dB RMS, with peaks at -3dB, you’ll achieve the optimal sound across all formats.
Q: What is RMS?
A: RMS has many functions, but for audiobooks it’s the value assigned to the overall volume level of an audio file. Audible will apply light dynamics processing once your audiobooks are submitted, so your production’s overall levels should not be too high or too low. For example, a production with a low RMS but loud peaks could end up with technical issues within the file, such as uneven narration levels, a high noise floor, etc.
Q: What is peaking?
Examples of peaks in an audiobook recording.
A: Peaks are the loudest part or parts of an audio file. If the script calls for a change from calm to excited, or from speaking to yelling, those excited or loud parts will most likely have the highest peaks. Our Audio Submission Requirements call for peaks to be under -3dB, which helps prevent distortion. If you have any 0dB peaks after mastering, you’ll need to adjust your limiter or normalizer settings and try again on your edited audio. If you have 0dB peaks before mastering, you’ll need to find out whether those peaks occurred during recording or after. If it happened during recording, you’ll need to lower your pre-amp’s level and re-record those lines of narration.
Q: What is an EQ?
A: An EQ (short for “equalizer”) is a tool that allows you to adjust the level of any frequency in an audio file. The typical frequency range that the human ear can detect is 20Hz to 20,000 kHz. The lower frequencies in this range are the bass/low range, while the middle is the mid-range, and high frequencies are the high range. Most EQ plug-ins will have high pass filter and a low pass filter. Using the high pass will remove any unwanted bass (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. I strongly recommend applying EQ before you master, as unwanted high or low frequencies can have an impact on the next step in your mastering process – applying a limiter. Removing a low frequency hum allows the limiter to more easily adjust to the narration at hand.
Q: What is a limiter?
A: A limiter is a dynamics processor. Applying a limiter lowers any high peaks in your audio, which allows the volume of the narration to be more even throughout. This lets you bring up the overall volume of your audio, which may be necessary to meet ACX’s RMS requirement (-18dB RMS to -23dB RMS). For example, if your max peak level is -4dB but your overall RMS level is -27dB RMS, your audio will look similar to the image below:
(Click images to expand)
In this case, you can use a limiter to lower all peaks by -3dB. Your max peak level would now be -7dB, as illustrated below.
Since ACX’s peaks requirement is -3dB, you can now raise the overall level of the audio by +4dB. That would bring your RMS to -23dB RMS, which is within our required range. Your mastered audio would then look something like this:
Now that we’ve gone over mastering as a concept, I think you’re ready to take a look at my Mastering Breakdown. It’s a great checklist to mark off each time you master an audiobook.
ALEX’S MASTERING BREAKDOWN
Assess all audio files to ensure no peaks or clipping exist in the audio.
Group all similar files together during the assessment so they can be processed at the same time.
Apply your “Mastering Chain” byusing the following processes, in order:
Remove all unnecessary low and high frequencies by applying EQ 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.
Listen to your audio after mastering to ensure the operation did not over-process or under-process the recordings. If the resultant audio is at one consistent volume with no change in dynamic level, you’ve likely over- If your audio has sudden spikes and drop offs (indicating it is too dynamic), you’ve under-processed.
That wraps up today’s lesson. I hope you all have a stronger understanding of audiobook mastering than when we started. Mastering your productions can seem daunting and technical, but once you know which aspects of your voice and recording space need to be accounted for, you’ll be able to apply the same processes over and over again with minimal changes. You’ll take your audiobook productions from good to great, and your listeners will appreciate the subtle improvements in sound quality you’ve achieved.
Class is back in session! I hope you learned a lot from my previous video, All About Noise Floor. Today, I’ve got a lesson on Room Tone, including a neat trick to save you some valuable time in the editing stage. Watch the video below closely; there will be a quiz afterward, and the first person to get all four questions correct will get an honorable mention (including a link to their ACX profile) in my next post.
Did you get all that? I hope so, because it’s time for that quiz I mentioned. Leave your answers in the comments to show how much you learned.
Audiobook room tone is defined as the _____ sound in your studio, and should be as close to perfect _____ as possible.
Room tone has three uses in your audiobook production:
The most effective way to utilize room tone in an efficient manner is to use your DAW’s _____ or _____ feature.
When using Pro Tools, the paste special feature is _____ on a Mac and _____ on a PC.
Hi, folks! I hope you’re ready to learn, because today, I’d like to kick off fall audiobook production lessons with three facets of your post-recording process:
Editing, QC, and Spacing
Audiobook editing is both an art and a skill. The aim is to achieve a clean, professional-sounding audiobook that elevates the source material. It consists of a two-step process commonly referred to as “Editing and QC.”
Step 1: Editing:
Remove extraneous sounds from your recording (mouth noises, pops, keyboard clicks, etc.).
Modify the pace of narration, if necessary.
When appropriate, portions of the recording that are edited out are replaced with clean room tone.
Step 2: QC (Quality Control):
Listen to the audio 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.
Once you’ve completed the QC step, you’ll rerecord the errors you’ve marked and re-insert them into your original audio files. These rerecorded sections of audio are sometimes called “pickups.”
A Pro Tools session featuring unedited, or “raw,” audio on top and edited audio below.
Audible Studios’ editors aim for a specific ratio of time spent on the edit or QC to the audiobook’s overall running time to ensure that these steps fall within the schedule and budget of the full production.
When editing, the ratio should be 3:1, or three hours spent editing for every one hour of recorded time.
For the QC process, the ratio should be 1.2:1, or 72 minutes of QC for every 60 minutes of recording.
If you find yourself working faster than this, I recommend a second edit and QC pass to make sure you haven’t missed an error. If you’re consistently taking longer than recommended, you may be focusing too much on certain aspects of the edit. Try listening to some samples and reading reviews on Audible to learn what really bothers listeners.
One way to stay within these guidelines is to speed up the playback in your DAW, so that you cover more ground than at the normal speed. While this may take some practice, it can help ensure that your editing is done quickly and correctly. If you go this route, I recommend you start at 1.2x speed, working your way up to 1.5x speed, as you get more comfortable.
When it comes to spacing, ACX’s requirements help ensure that your audiobook productions stand shoulder to shoulder with all the titles on sale at Audible, Amazon, and iTunes. Our requirements state:
Each uploaded file must have between 0.5 and 1 second of room tone at the head, and between 1 and 5 seconds of room tone at the tail.
Editor’s Note: We’ve since adjusted our spacing requirements to improve the listener experience. The current requirement states that each uploaded file must have no more than 5 seconds of room tone at the beginning and end.
Why is this so important? Think of the spacing within your audiobook as the layout of words on pages and of pages within chapters of a print or eBook. Without proper spacing denoting the end of a scene or beginning of a new chapter, your listener could feel lost within the book, and the impact of your narration may be lessened. The easiest way to follow this requirement is to paste in the appropriate amount of clean room tone at the head and tail of each file.
I hope this gives you a good understanding of one of the most important aspects of audiobook production. Check out my other posts for more audiobook production education, and come back soon for more tips straight from The Audio Scientist.
Quick Tips for Editing and Spacing:
Make sure you have clean room tone. If you don’t, you could be creating more problems than you’re solving.
Record new room tone any time you change your microphone or studio settings. The old room tone may not match the sound of the new recording you are applying it to.
Always wear headphones. You need to be in an isolated environment to ensure the narration stays natural and any cut is seamless.
Get into the habit of marking everything. If you find a click, pop, noise, or QC error, make sure you mark the instance within your DAW! That way, when you go back to make the edits, you won’t have missed anything.
We’d like to introduce you to the newest member of the ACX team, Alex the Audio Scientist. Alex has a degree in Audiobook Studies from ACX University, and he’ll be stopping by the blog from time to time to explain some key aspects of audiobook recording and production. So without further ado, take it away Alex!
Nice to Meet You!
Hi everyone I’m excited to share my knowledge of all things audiobooks and help you improve your ACX productions. Before today’s lesson, I hope you’ve read previous posts on this blog regarding home studio setup, because today I’ll cover a common problem with voice recording spaces: a high noise floor. Enjoy the video below, and take good notes – there’ll be a quiz afterward!
And we’re back. Ready for that quiz I mentioned? Let’s see how much you learned. Leave your answers in the comments below. The first person to get every answer correct will get a shout out in my next post!
The noise floor is the ________ level of background noise in a recording, when no narration is taking place.
A high noise floor in a home studio can be caused by ________, ________, ________, ________, or ________.
Its best to address your noise floor issues during the ________ stage.
I recommended using a ________ to remove unwanted frequencies, such as a low rumble.
The appropriate frequency range to target the removal of this low rumble is usually between ________ and ________ Hz.
The ACX Audio Submission Requirements call for a noise floor no higher than ________ dB RMS.
Welcome back to the second half of my two-part home studio setup series. Last week I covered where to place your home studio, how to properly soundproof it, and the basic equipment you’ll use in it. Today, I’d like to share real-world examples from three Audible Approved Producers. Let’s look at (and listen to) the great results a home studio can produce.
Visible Sound Audiobooks
The controlling and deadening of acoustic reflections in her bedroom and specifically around the microphone is one of the main contributing factors to the professional audio quality of her recordings – Ben Glawe of Visible Sound Audiobooks.
This home studio photo comes to us from Visible Sound Audiobooks, an Audible-Approved Producer whose operations primarily take place in a Brooklyn bedroom. How does this team achieve their professional sound quality in the midst of the country’s busiest city? House-narrator Christine Papania explains:
The biggest noise problem with my bedroom was my window, which overlooks a a noisy street in Brooklyn as well as a park. I bought special blackout curtains which block out light and sound from windows, which lowered the outside noise to acceptable levels. My laptop fan was also leaking noise into the microphone, but the addition of a silent laptop cooling pad fixed the problem.
Now we’ll hear a recording from Visible Sound’s space. You might be surprised how good it sounds!
Kate Udall got her start as a narrator at Audible Studios. After working on her production chops and securing some great ACX titles, she earned herself the Audible-Approved Producer distinction. Kate’s studio is a great representation of an effective DIY home recording setup.
According to Kate
We call it Fuzzy Jail around here. It is made of blankets, the size of a cell and I am often inside in locked-down solitary confinement.
Kate uses thick packing blankets to isolate her recording studio from the rest of the room’s noises, which also provides the added benefit of reducing sound reflections that may otherwise occur on the side wall to the left. Her microphone is situated in front of an Auralex Mudguard, a great tool that can further reduce sonic clutter that occurs in home recording environments. She is also wise to set up an external monitor and other necessary components so that her laptop, which sits outside of the recording environment, does not introduce more artifacts and noises into the recorded signal.
Lets listen to a recording from Kate’s Studio:
Stephen Bel Davies
Our final example shows the upper limits are of home audiobook production. Yes, you are looking at a home studio! This photo comes to us from veteran narrator Stephen Bel Davies.
Located in his Manhattan bedroom, this Studiobricks* installation is the top-of-the-line option for home recording due to its incredible noise-blocking capabilities and reflection controlled environment. Acoustic treatments on all walls, as well as the ceiling, guarantees a deadened recording space with extremely dampened artifacts and reflections. While Stephen is able to achieve a stunning -60dB of sound reduction with this setup, it doesn’t come cheap. These installations will set you back about at least $4,000 before factoring in installation costs. Still – one can dream!
Here is a bit of audio produced in Stephen’s studio.
While Whisper Rooms are an ideal recording environment for any audiobook narrator, they are not necessary to produce a great recording. The most important consideration during an ACX production is consistency – both in practice and in aesthetic. For this reason, after you’ve installed your home studio, I strongly encourage you to read up on my four-part series, How to Succeed at Audiobook Production, which goes over methodologies to ensure success with your new audio production system.
How do you achieve a professional recording? Leave your feedback in the comments below.
(This section originally misidentified Mr. Bel Davies home studio as a WhisperRoom.)
Welcome to the latest musings from Andrew the Audio Scientist. Today, I’ll be addressing the most essential component of a successful ACX audiobook production: constructing a home recording studio. You may be surprised to find how clean and clear your narration can sound after implementing just a few of the techniques and products below into your own studio setup. Let’s take a look at the two main aspects of a solid studio arrangement.
The most important consideration when building your home studio is its location. The ideal recording space dimensions are rectangular (NOT square), with low ceilings and 90º corners. Closets and other enclosed spaces make perfectly great recording spaces after implementing a few basic room treatments.
Reflection absorption materials, such as the ones detailed on the ACX Beginners Amazon Wish List can make all the difference. The primary reflection points that should be addressed are any surfaces behind the microphone and on the side walls, at a distance exactly half-way between your sitting position and the microphone stand. If you want to go the DIY route, the same effect can be achieved by hanging your old winter coats on the walls, or even throwing up moving blankets where clothing is not an option. The idea is to use fabrics that are thick and provide ample absorption so that once sound hits the material, it stops dead in its tracks.
Isolation is an important consideration for your room, too. An important step in the audiobook production process is the pasting of clean room tone on top of edits and other extraneous noises. Doing so can be greatly inhibited, though, by a non-ideal recording space. You may find the room tone to be too noisy to affect any real sonic improvements. To combat this and other noise problems, make sure to isolate outside noises from your recording space by hanging blackout curtains at all windows, and insulating your room’s open cracks and crevices. However, note that there are some rooms where even the most expensive room treatments are unlikely to make a big impact.
Avoid installing your studio in large rooms such as kitchens and sun rooms. These will cause undesirable echo and reverberation, and result in a muddy sound.
Small rooms with reflective surfaces like bathrooms should also be avoided, because the porcelain and mirrors will send your voice flying across the room without remorse.
Last but not least, recording outdoors is a big no-no. While the sounds of nature can be pleasant, squawking birds and passing cars are not sounds that belong in audiobook productions.
This is pretty obvious – if you want to record your voice at home, you’ll need a microphone. Not so obvious, however, is the kind of microphone you need to purchase. At ACX, we recommend a large-diaphragm cardioid condenser microphone. These microphones are typically more accurate and clean than other types of vocal microphones, but are also more sensitive to recording mistakes. You’ll need to adhere to some setup best practices to get the most out of your purchase:
Placement – A microphone is best set up at a point no further than 40% away from the front wall. Ideally, the microphone would be placed half-way between the side walls.
Height – Microphones placed at or below mouth-level tend to pick up more “body” of a voice, while placement above the mouth (closer to the nasal cavity) capture a more “bright” and airy sound. However, this is a very personal aspect to studio configuration that is best left to experimentation.
Diagram of a ideal mic placement within a home studio
Distance – It is never necessary to stand the microphone further than 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 does not already come with one. (For you DIYers, you can also construct your own pop filter out of – no joke – some pantyhose and flex tubing, as demonstrated in this Lifehacker article)
One of our favorite starter microphones of this type is the Rode NT1-A, which can be found on the ACX Beginners Amazon Wish List. The NT1-A kit available on Amazon comes with a pop filter and all of the mounting hardware needed to get started. This, in conjunction with the Blue Icicle XLR-to-USB microphone interface and a solid microphone stand, provides an excellent starter ACX production system.
Following these basic rules for home studio setup will allow you to transform the appropriate area of your living space into a great sounding vocal booth. Check out Part 2 to see and hear examples of some real-life Audible Approved Producers home studios.
Now that you’re caught up, let’s move on to the fourth and final part of my series: encoding and file delivery.
Rounding The Final Corner
Upon a successful master, your audiobook production is not quite finished. Keeping that in mind, watch the final video in our series, and review the key points I discuss after.
The Home Stretch
I recommend you perform another final QC pass on your audio before moving on to encoding and delivering your audio. After putting so much effort into your production, the last thing we want to do is send an audio review notice to fix missing chapters or out-of-order audio files. The post-mastering QC pass needn’t be as in-depth as what I recommend in the article on editing; it could be as simple as verifying the volume levels are meet our specifications, that the content is complete, and that the audio files are numbered and named in the proper order.
If everything looks ready, then we can begin the encoding process. I cover this in more detail in my post, Encoding Audio with Andrew the Audio Scientist, but I’ll summarize here. That post contains a link to our instructions detailing how to encode your audiobook to ACX specifications using the free and cross-platform fre:ac encoding software.
Also be cognizant of ACX’s file-level requirements. The encoding options you choose can potentially cause the run-time or the file size to go over our specifications. Each file must contain a single chapter with a length no longer than 120 minutes..
Crossing the Finish Line
Once you verify your audio complies with our MP3 encoding and file-level requirements, you’re ready to upload our audio to the ACX production manager! Here are some last-minute tips that could potentially save you from an audio review notice.
1. Be smart about your sample. The retail sample you provide will likely be a customer’s first glimpse into your work, so make this moment count! I recommend grabbing the audio from an early point in the book, so you don’t give away plot developments. Also, be mindful of the ACX sample requirements, which expressly prohibit erotic/mature content. If your book is on the wilder side, find a section that is appropriate for all audiences.
2. Double-check your book’s chapter order when uploading your files. Files arrive to ACX in the same order as they are uploaded to the Production Manager. Doing this last check will make the QA process simpler and faster, allowing us to get your title on sale more quickly.
3. Ensure your file names are clear and concise. To help ACX best understand your audio, I recommend naming your audio using a template such as:
Since we are at the end of the How to Succeed at Audiobook Production series (but not the end of my regular contributions to the blog), I want to take this opportunity to thank our users, subscribers and readers for your loyal viewership.
But don’t worry, I’ll be back with more audiobook production tips soon. In the meantime, share your own with your fellow readers in the comments below!
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.
Mastering the Art of 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.
Now, let’s watch part three of How to Succeed at Audiobook Production, and after, review the mastering tips I suggest below.
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.