What Is ACX? How to Publish an Audiobook on Audible

Audible controls roughly 63% of the U.S. audiobook market, yet most indie authors have never heard of the platform that actually gets their book onto it. That platform is ACX — and understanding what is ACX and how to publish an audiobook on Audible through it is one of the most valuable things you can do for your author business in 2025.

What Is ACX?

ACX stands for Audiobook Creation Exchange. Launched by Audible on May 12, 2011, it's an Amazon-owned marketplace that connects authors, rights holders, narrators, and audio producers — and serves as the official upload portal for distributing audiobooks to Audible, Amazon, and Apple Books simultaneously. Think of it the way you think of KDP for ebooks: ACX is the backend infrastructure that makes your audiobook visible to millions of listeners without requiring a traditional publishing deal.

More than 400,000 audiobooks have been produced through ACX since its launch, making it the single largest audiobook production and distribution pipeline for independent authors in the world. The Audio Publishers Association's 2025 Consumer Survey found that 51% of Americans aged 18 and older — roughly 134 million people — have listened to an audiobook. That's a massive, growing audience that ACX gives you direct access to.

ACX is free to join. You don't pay a listing fee. Instead, ACX earns its cut through the royalty structure it applies to your sales.

How ACX Royalties Work

This is where authors often get confused, so let's be precise.

ACX offers two distribution arrangements:

Exclusive distribution (40% royalty): Your audiobook sells only through Audible, Amazon, and Apple Books for a 7-year term. You earn 40% of the retail price on each sale.
Non-exclusive distribution (25% royalty): You're free to distribute your audiobook elsewhere — other retailers, library platforms, your own website — but your ACX royalty drops to 25%.

For most debut audiobook authors, the exclusive 40% rate is worth considering carefully. Audible's listener base is enormous, and the discoverability tools available on the platform can carry significant weight early in a book's life. That said, if you're building a wide distribution strategy across platforms like Libro.fm, Kobo, or library aggregators like Findaway Voices, the non-exclusive path preserves your flexibility.

One important note: if you produce your audiobook through ACX's marketplace (by hiring a narrator through the platform), uploading it anywhere else would violate your agreement. Always read your production contract before signing.

The Two Ways to Use ACX as an Author

ACX isn't just a distribution portal — it's also a production marketplace. Authors can use it in two distinct ways.

Option 1: Hire a Narrator or Producer Through ACX

You post your book on ACX, audition narrators who submit samples, and either pay them a per-finished-hour (PFH) rate or offer a royalty-share arrangement. Royalty-share means you pay nothing upfront — the narrator receives a percentage of your royalties instead. This sounds appealing when you're cash-strapped, but it comes with tradeoffs: royalty-share locks you into ACX exclusivity for 7 years, and experienced narrators often prefer flat-fee work.

Professional narrators typically charge anywhere from $200 to $400+ per finished hour. An 80,000-word novel produces roughly 8–9 hours of finished audio, which means narrator fees alone can run $1,600–$3,600 before you've touched editing or mastering.

Option 2: Upload a Finished Audiobook You Produced Yourself

This is the path most indie authors take when they've already recorded or produced their audio elsewhere. You simply upload your completed, ACX-compliant files directly. ACX reviews them, and if they pass quality assurance, your audiobook goes live across Audible, Amazon, and Apple Books — typically within 10–14 business days of approval.

This second path is increasingly popular because AI voice technology has made self-production fast and affordable. If you want to understand the full production side of that workflow, our complete guide to AI audiobooks walks through everything from script preparation to final export.

ACX Audio Specifications: What You Need to Know

ACX has strict technical requirements. Submitting files that don't meet them will result in rejection and delays. Here's what your audio must comply with:

Format: MP3, constant bit rate (CBR), 192 kbps or higher
Sample rate: 44.1 kHz
Channels: Stereo or joint stereo
Noise floor: -60 dB or lower
Room tone: 1–5 seconds of room tone at the start and end of each file
Peak levels: No higher than -3 dB
RMS loudness: Between -23 dB and -18 dB
File structure: Each chapter as a separate file, plus an opening credits file

These are collectively known as ACX-compliant audio specs. Meeting them isn't optional — ACX's QA team checks every submission against these standards. If your files are too loud, too noisy, or improperly formatted, you'll receive a rejection notice and need to reprocess and resubmit.

Most professional recording software (Adobe Audition, Audacity, Logic Pro) can handle normalization and export settings. If you're using an AI audiobook platform, check whether it exports ACX-compliant MP3s automatically — this saves significant post-production time.

Step-by-Step: How to Publish an Audiobook on Audible via ACX

Here's the full process from account creation to going live:

Create an ACX account at acx.com. You'll log in with your Amazon account credentials.
Claim your book. Search for your title using its ISBN or ASIN from Amazon's catalog. If your book isn't on Amazon yet, you'll need to publish it there first (even as a free Kindle listing) so ACX can find it.
Set up your audiobook profile. Add your book's description, target audience, and any notes for narrators if you're using the marketplace. If you're uploading finished audio, you'll skip this step.
Choose your production path. Select "I have a finished audiobook" if you're uploading pre-produced files, or post an audition request if you want to hire through ACX.
Upload your audio files. Submit your chapter files plus the opening credits file, all meeting ACX's technical specs.
Complete your retail information. Write your audiobook description (this appears on the Audible product page), set your language, and confirm your rights declaration.
Choose your distribution type. Exclusive (40% royalty) or non-exclusive (25% royalty).
Submit for QA review. ACX's quality assurance team reviews your files. This typically takes 10–14 business days for first-time submissions.
Go live. Once approved, your audiobook appears on Audible, Amazon, and Apple Books. Royalties are paid monthly by check or direct deposit.

Common Reasons ACX Rejects Audiobook Files

Understanding why submissions fail can save you weeks of back-and-forth:

Background noise above -60 dB — even subtle HVAC hum or room echo will trigger rejection
Incorrect loudness normalization — files that are too quiet or too loud relative to the -23 to -18 dB RMS window
Missing room tone — each file needs that 1–5 second buffer at the start and end
Inconsistent audio quality across chapters — if chapter one sounds noticeably different from chapter eight, QA will flag it
Incorrect file naming — ACX expects a specific naming convention; check their current submission requirements before uploading

Is ACX Still the Right Choice in 2025?

ACX remains the dominant path to Audible, which still represents the largest share of audiobook sales in the English-language market. For authors who want maximum reach with minimum complexity, uploading to ACX and accepting the exclusive rate is a defensible strategy — especially for a first audiobook.

That said, the landscape has shifted. Platforms like Findaway Voices (now part of Spotify) and Draft2Digital offer wide distribution to 40+ retailers, including library platforms like OverDrive and hoopla, which ACX doesn't cover. If your readership skews toward library borrowers or international markets, going wide via a distributor and accepting the 25% ACX rate may net you more total revenue.

The decision ultimately comes down to where your readers already are. Romance and thriller authors with established Audible audiences often do better leaning into exclusivity. Nonfiction authors with strong library or international sales may benefit from going wide.

For authors who want to produce their audio quickly and affordably before making that distribution decision, StoryVox generates ACX-compliant MP3 audiobooks from your manuscript — with chapter-by-chapter control and 15+ voices across 8 languages — starting at around $15–30 for a typical novel.

The audiobook market has 134 million potential listeners in the U.S. alone. The technical and contractual details of ACX are learnable in an afternoon. The harder question is why you haven't started yet.