An ACX submission checklist keeps your delivery organised so you never face a technical rejection. The platform enforces strict audio specifications. If your files deviate on loudness, format, peak levels, or silence padding, they fail the initial automated analysis.
The process of moving from a finished recording to a published audiobook involves nine phases. You must prepare the raw files, master the audio to spec, append the correct room tone, export in the proper format, standardise your file names, cut a retail sample, frame the book with credits, upload the package, and wait for human review.
If you handle these steps methodically, your audiobook sails through. This guide breaks down each requirement, showing you exactly what to do and why it matters. To see if your files are ready right now, run them through the Free ACX Check. The tool sits in your browser and measures every spec against the platform target.
What is the ACX submission checklist?
Here is the entire technical journey from raw recording to platform approval. Every chapter file must meet these standards.[1]
| Step | What to do | What it satisfies | ACX requirement |
|---|---|---|---|
| File prep | Clean the audio, remove mistakes, standardise to 44,100 Hz mono WAV. | Source consistency | 44.1 kHz, mono. |
| Mastering | Compress, normalise, gate, and limit the audio. | Volume and clarity | RMS -23 to -18 dBFS, True Peak below -3 dBFS, Noise floor below -60 dBFS. |
| Silence padding | Paste recorded room tone at the start and end. | Pacing and separation | 0.5 to 1 s head, 1 to 5 s tail. No digital silence. |
| Encoding | Export the finished files to MP3 using Constant Bit Rate. | Delivery format | MP3 format, 192 kbps CBR minimum. |
| File naming | Number your track files sequentially. | Chapter ordering | Clear numerical progression (e.g. 01_Title.mp3). |
| Retail sample | Pick a compelling excerpt with no explicit content. | Storefront preview | 1 to 5 minutes duration, exact ACX audio specs. |
| Credits | Record dedicated opening and closing tracks. | Metadata match | Title, author, narrator named explicitly. |
| Upload | Place files in the ACX project dashboard. | Platform intake | One file per chapter. |
| Wait | Monitor your email for the status transition. | Approval | Wait 10 to 14 business days. |
How do I prepare my files before mastering?
Start with clean raw audio. ACX requires a sample rate of 44,100 Hz and a single mono channel.[1] Video software often defaults to 48,000 Hz stereo, so standardise your format immediately. Most DAWs let you batch convert these parameters before you begin post-production.
Edit your dialogue. Remove mistaken takes, heavy mouth clicks, and intrusive breaths. Mastering will amplify everything in the file, so an unedited click becomes much louder after processing. Keep the files in a lossless format like WAV during this stage. Encoding to MP3 degrades the audio slightly, so you only want to do it once at the very end.
For an inside look at a popular DAW setup, read the Audacity audiobook mastering guide.
How do I master my files to ACX specs?
Mastering shapes your raw performance to fit standard consumer devices. ACX measures three interconnected numbers to ensure a good listening experience: RMS loudness, true peak, and noise floor.[1]
Your RMS loudness must sit between -23 and -18 dBFS. RMS is the average energy of your voice. If it falls too low, listeners cannot hear you over highway noise. If it pushes too high, the audio feels fatiguing. Target -20 dBFS. This places you squarely in the middle of the window, leaving room for natural dynamic variation.
Your true peak must stay below -3 dBFS. Peaks are the loudest single moments in the file. The -3 dBFS ceiling provides headroom so the platform can transcode your file to different formats later without causing digital distortion. Use a true-peak-aware limiter rather than a standard peak limiter to catch clipping that falls between digital samples.
Your noise floor must rest below -60 dBFS. ACX wants silent moments to actually sound silent. The most common technical roadblock is that turning up your quiet narration also turns up the background hiss. If you struggle here, refer to the audiobook noise floor guide for the solution. If you want the technical heavy lifting handled for you, ChapterPass processes all these variables automatically.
What are the rules for silence padding?
ACX uses silence to help listeners transition between chapters and to give software players defined markers for navigation.[1] You must include 0.5 to 1 second of head silence at the start of the file. You must include 1 to 5 seconds of tail silence at the end of the file.
The critical detail is the type of silence. You cannot use digital silence (absolute zero signal). Complete digital silence sounds unnatural and creates an audible click when the speaking abruptly begins. You must use room tone. This is the natural, quiet ambient sound of your recording booth. Record thirty seconds of quiet room tone after a session, copy short clips of it, and use those clips to pad your chapter files.
How do I encode my files for ACX?
Once you finish mastering and padding the audio, you must export it for delivery. ACX rejects WAV or FLAC files. You must submit MP3 files encoded at 192 kbps or higher.[1]
The encoding must use Constant Bit Rate (CBR). Many audio programs default to Variable Bit Rate (VBR) to save file sizes, but VBR causes playback glitches in older smartphone apps and dedicated audiobook players. In your DAW export menu, select MP3, choose CBR, and select 192 kbps.
If you receive a notification about bitrate failure, it almost always means a VBR setting slipped into the export process. The ACX rejection fix guide explains exactly how to decode these failure notices.
How should I name my ACX files?
ACX reads your file names to sort the chapters in the upload dashboard.[2] If you name them haphazardly, you drag the chapter tracks into the wrong order, confusing the listener.
Standardise your naming convention. Begin every file with a number. Use leading zeros so alphabetical sorting works correctly. For example, use "01_Prologue.mp3", "02_Chapter1.mp3", and "11_Chapter10.mp3". File names are invisible to the end listener, but keeping them strictly structured prevents you from assigning Chapter 4 to the Chapter 5 slot in the submission portal.
How do I choose my retail sample?
The retail audio sample is the preview track customers hear on Audible before they buy. It heavily influences sales. The sample must run between 1 and 5 minutes long.[3] It must meet the exact same audio specifications (loudness, peak, noise floor) as the main chapters.
Pick a section from early in the book that hooks the listener. Do not include explicit content, spoilers, or the opening credits. A strong dialogue exchange or an intriguing character introduction works best. Take a copy of your mastered main chapter, cut the specific segment, add your room tone to the head and tail, and export it as a separate MP3.
If you are unfamiliar with the broader context of audio distribution, the ACX audio requirements breakdown clarifies how this sample integrates with storefronts.
What goes in the opening and closing credits?
Every ACX project requires dedicated opening and closing files.[4] These act as the title page and the back cover of the listening experience.
The opening credits file must state the title of the book, the author name, and the narrator name. Do not bury this information in a sweeping introduction. Keep it simple and clear. The closing credits file must state "The End" or a variation like "This has been an Audible production of...".
These files must meet all standard ACX technical measurements, including head and tail silence. Treat them identically to your main chapters during the mastering phase.
How do I upload my files to ACX?
Log in to the ACX dashboard and navigate to your active project. You will see an interface called the Audio Submission Manager. This manager displays empty slots for your opening credits, main body files, closing credits, and retail sample.
Click each slot and upload the corresponding MP3 file. The platform assigns the chapters sequentially based on the order you arrange them in this screen. Listen to the first few seconds of each uploaded track through the online preview player to confirm you placed the right audio in the right container. If everything aligns, press submit to send the project for analysis.
How long does ACX take to approve an audiobook?
Once you press submit, the system runs an automated analysis. If your files fail the loudness, peak, or noise parameters, you receive an email within minutes or hours. Fix the specific number requested and upload the replacement file.
If the automated review finds no technical faults, the project joins the queue for human quality review. A team member listens to sections of the audio to assess pacing, performance, and manuscript accuracy. This phase typically takes 10 to 14 business days. If the reviewer approves the content, they pass the title to retail distribution. Your title then appears on Audible, Amazon, and iTunes within a few days.
Common Questions
Do I need to submit a single giant MP3 file for the whole book?
No. ACX explicitly requires you to break the book down.[1] You must submit one file per chapter, plus individual files for the opening credits, the closing credits, and the retail sample.
Can I use music in the opening credits?
Yes, but only if you own the distribution rights to the music. Free background tracks from the internet often trigger copyright flags. The music must also conform to the same true peak and RMS loudness targets as the narration.
Why does my DAW export dialog warn about variable bit rate?
Variable bit rate dynamically changes file quality to save hard drive space. ACX requires Constant Bit Rate (CBR) because it streams reliably across all legacy devices.[1] Ignore the warning, select CBR, and export at 192 kbps.
What if a chapter is incredibly short, like 30 seconds?
ACX does not specify a minimum duration for standard chapters. You still must hit the loudness limits and include the proper head and tail room tone. Only the retail sample has a hard minimum of one minute.[3]
Do I have to master the retail sample differently?
No. The retail sample is subjected to the same automated analysis as your main chapters. The easiest method is to take your already-mastered chapter, trim out the section you want, add the room tone, and export.
What happens if I find a mistake after submitting?
If the project is still in human review, you cannot alter the files. If the project is approved and live on retail stores, you can use the ACX dashboard to flag specific audio files for replacement.
If you want to skip manual limiters, complicated export settings, and tedious loudness calculations, you can automate the process. ChapterPass masters your audiobook files to meet every ACX metric perfectly. The tool handles formatting, controls the background noise, and pads the necessary room tone. Try it today on the pricing page or test a single track completely free.