What Is the ACX Audio Submission Checklist?

The ACX Audio Submission Checklist is a formal set of technical and content specifications that every audiobook must meet before it can be published on Audible, Amazon, and iTunes through ACX (Audiobook Creation Exchange). It acts as the final gatekeeper between your finished recording and the worldwide audience of listeners. Understanding this checklist is not optional—it’s the difference between a smooth launch and repeated rejections that cost you weeks of time.

ACX receives thousands of submissions every month, so their review process is automated and unforgiving. Files that violate even one requirement can be flagged and returned without detailed feedback. The checklist is designed to make compliance transparent: every requirement is published, every test is repeatable, and every successful submission follows the same rules. This article breaks down every component of that checklist, explains why it matters, and shows you exactly how to verify your work before you hit submit.

The Complete Breakdown of the ACX Audio Submission Checklist

The checklist can be grouped into five primary categories: audio quality, file format and encoding, file naming and organization, chapter markers, and metadata. Each category contains multiple specific requirements. We’ll cover each in depth.

1. Audio Quality Requirements

Audio quality is the most subjective yet most heavily enforced part of the checklist. ACX expects professional-grade sound with no audible flaws. Specifically:

  • No background noise – The noise floor must be below -60 dBFS. Any consistent hum, hiss, or room tone that rises above this threshold will fail review.
  • No distortion or clipping – Peaks should never reach 0 dBFS. Ideally keep maximum levels at -3 dBFS or lower to prevent digital clipping.
  • No echoes or reverb – Recordings made in untreated rooms often have slap echo or boxiness. These must be removed with acoustic treatment or post-production editing.
  • Consistent volume – The loudness of the narration must be uniform across all chapters. ACX uses an RMS (root mean square) measurement between -18 dB and -23 dB for the entire audiobook. Many producers target -20 dB RMS.
  • No artifacts – Clicking, popping, mouth noises, and breaths that are distracting must be edited out. Normal breaths are acceptable, but loud, sibilant, or plosive breaths need to be reduced or removed.

Why this matters: A listener’s brain is extremely sensitive to changes in ambient noise and volume. If you record Chapter 1 in a carpeted room and Chapter 2 in a kitchen, the shift will be jarring. The checklist exists to guarantee a seamless listening experience.

2. File Format and Encoding Specifications

ACX mandates that all audio files be delivered as MP3s with specific encoding parameters. You cannot submit WAV, FLAC, or any other format unless you are working with a producer who has special arrangements.

  • File format: MP3 only.
  • Bit rate: 192 kbps constant bit rate (CBR). Variable bit rate (VBR) is not accepted. Always set your encoder to CBR 192.
  • Sample rate: 44.1 kHz. Do not use 48 kHz or any other sample rate. A 48 kHz file submitted at 192 kbps will be rejected.
  • Channels: Mono or stereo. Narrated audiobooks are almost always mono. Using stereo doubles the file size without benefit, but it is technically allowed.
  • Joint stereo: If you export in stereo, joint stereo encoding (mid/side) is not accepted. Use simple stereo or, better, export in mono.

To meet these requirements, export your final mastered audio as a 24-bit WAV or AIFF at 44.1 kHz, then convert to MP3 using a tool like Apple’s AudioMover, free software like Audacity (with LAME encoder), or a dedicated batch converter. Always double-check the exported file properties in a media info program.

External link: Official ACX Audio Submission Requirements (ACX Help).

3. File Naming and Organization

ACX uses your file names to automatically map chapters. Incorrect naming is one of the most common reasons for rejection. The naming convention is simple but rigid:

  • Each file must be named exactly as the chapter title appears in your ACX project (including punctuation and capitalization). For example: Chapter 01 – Introduction.mp3.
  • Do not add extra numbers, underscores, or version tags (e.g., v2_final_chapter01.mp3).
  • All files must be submitted in a single ZIP archive. The filenames inside the ZIP must match the chapter order exactly.
  • Do not include any extraneous files in the ZIP – no cover art, production notes, or text files.

Before zipping, double check that the alphabetical sort of your file names matches the chronological order of your audiobook. If you have chapter numbers like “Chapter 1” and “Chapter 10”, the system will sort alphabetically, so “Chapter 10” will appear before “Chapter 2”. To avoid this, use leading zeros: “Chapter 01”, “Chapter 02”… “Chapter 10”.

4. Chapter Markers

Chapter markers within the MP3 files are used by Audible to allow listeners to skip to the next chapter. The requirements are:

  • Each MP3 file should contain exactly one chapter marker at the very beginning of the audio.
  • Do not embed multiple chapter markers within a single file. ACX’s system will treat multiple markers as an error.
  • The chapter title in the marker metadata should match the file name and the ACX project chapter title.
  • Markers must be placed at 00:00.000 – not one second into the audio.

To set chapter markers, use an MP3 tagging tool like Mp3tag, iTunes, or Adobe Audition. Simply edit the “Chapter” or “Track number” field if your software supports it. For batch processing, many producers use a script or a dedicated audio processing tool to automate marker insertion.

5. Metadata Requirements

Metadata might seem minor, but ACX checks it against your project details. If they don’t match, the system flags the submission. Required metadata fields include:

  • Title: Exactly as it appears in your ACX project, including subtitle if applicable.
  • Author: The author name as registered in your ACX account.
  • Narrator: The narrator name as listed on the project.
  • Copyright year: The publication year.
  • Genre and language: Must match the ACX project settings.

You can add metadata using tagging software or directly in your DAW during export. Many producers prepare a template with all correct metadata and apply it to every file before zipping.

How to Use the Checklist Effectively (Step by Step)

Now that you know what the checklist covers, let’s build a practical quality control workflow. Follow these steps before every submission.

Step 1: Prepare a Master Copy

After editing and proofing, create a single continuous master audio file in WAV or AIFF at 44.1 kHz, 24-bit. This is your “audiobook master.” It should have consistent levels, edited noises, and required loudness.

Step 2: Split into Chapters

Using audio editing software (Audacity, Reaper, Adobe Audition, etc.), mark chapter boundaries and export each chapter as a separate WAV file. Name each file exactly as it will appear in ACX (e.g., “Chapter 01 – The Beginning.wav”).

Step 3: Export to MP3

Convert each WAV to MP3 with the following settings:

  • Format: MP3
  • Bit rate: 192 kbps CBR
  • Sample rate: 44.1 kHz
  • Channels: Mono (or stereo, but mono is standard)
  • Encoder quality: Standard or High (do not use “low” or “fast”)

After conversion, check the file properties in a media player to confirm that the bit rate is exactly 192 kbps and sample rate is 44100 Hz.

Step 4: Add Chapter Markers and Metadata

Use a tagging tool to embed:

  • Chapter marker at 00:00.000 in each file.
  • Metadata: title, author, narrator, copyright.
  • Album name (usually the audiobook title).
  • Genre: “Audiobooks” or as specified in ACX.

Step 5: Validate Every File

Play back each MP3 file from start to end. Listen for:

  • Consistent volume from chapter to chapter.
  • No pops, clicks, or digital artifacts.
  • Accurate chapter endings and beginnings (no silence gaps longer than 0.5 seconds).

Many producers run a loudness analysis tool (e.g., Youlean Loudness Meter) to verify RMS levels are between -18 and -23 dB.

Step 6: Create the ZIP Archive

Select all MP3 files (no other files) and compress them into a single ZIP. Ensure that the ZIP file name follows ACX naming conventions (usually the audiobook title with no special characters). Do NOT use RAR, 7z, or any other compression format.

Step 7: Upload and Perform a Test Listen

ACX provides a preview player after you upload. Use it to check a few chapters. If you can play the entire audiobook through without issues, you’re likely ready. If you hear a glitch, correct the file and re-upload.

Common Mistakes and How to Avoid Them

Even experienced producers make errors. Here are the most frequent reasons for ACX rejection and how to avoid them.

  • Incorrect bit rate: Using VBR or lower than 192 kbps. Always double-check the export settings. Use a batch encoder with a preset.
  • Background noise: Failing to noise-gate or noise-reduce. Use spectral analysis to see noise floor. For difficult recordings, consider using iZotope RX for noise reduction.
  • Volume mismatches: One chapter is louder than the next. Use normalization and loudness matching across all chapters. Match RMS to within 0.5 dB.
  • File naming errors: Extra characters, wrong case, or missing leading zeros. Create a checklist and verify each file name against the ACX project.
  • Missing or duplicate chapter markers: Use a dedicated tagging tool that can batch-add markers.
  • Wrong sample rate: 48 kHz instead of 44.1 kHz. Always check your DAW export settings.

Tools to Help You Automate Compliance

Manual checking is tedious. Use these tools to automate parts of the process:

  • Audacity + LAME: Free, open-source audio editor. Can batch export MP3s with custom settings.
  • Mp3tag: Free tag editor that can add chapter markers and metadata in bulk.
  • Checkmate: An online service that analyzes your audio files for ACX compliance (Audiobook Mastery Checkmate).
  • Loudness Analyzer: Standalone or plugin (e.g., Youlean, TBProAudio dpMeter).
  • Batch converter: Switch Audio Converter, dBpoweramp, or Foobar2000 for converting to MP3 with exact settings.

Benefits of Following the Checklist Meticulously

Adhering to the ACX Audio Submission Checklist is not just about avoiding rejection—it directly affects your reputation and income as a narrator or author-publisher. Here are the concrete benefits:

  • Faster approval times: Compliant files often pass within 24–48 hours. Resubmissions can take 2–4 weeks due to reviewer backlogs.
  • Higher listener satisfaction: Consistent audio quality means fewer complaints and returns. Listeners are more likely to leave positive reviews and recommend your book.
  • Professional credibility: ACX reviewers see thousands of submissions. A clean submission marks you as a professional, which can lead to more opportunities (e.g., preferred narrator status).
  • Less stress: When you have a reliable process, you remove the anxiety of “will it pass?” and can focus on creating more content.
  • Repeat business: Authors who produce clean audiobooks are more likely to hire the same narrator or use the same producer for future projects.

Final Advice: Build a Custom Checklist Based on This Article

Print out the categories and specific requirements listed in this article and create a physical or digital checklist. For each chapter, verify every point. Even better, work with a partner or a proof-listener who can go through the checklist independently before you upload. Two sets of ears catch more errors than one.

Remember that ACX occasionally updates their requirements. Always check the official ACX help page before each major project to ensure your checklist is current. Additionally, the Audible Quality Standards guide provides supplementary details that apply to the distribution side.

The ACX Audio Submission Checklist is your best friend during post-production. Embrace it, automate it, and never submit a file that hasn’t passed every test. Your listeners—and your approval rate—will thank you.