Step‑by‑Step Guide to Finalizing Your Audiobook for ACX Submission

Creating an audiobook is an exciting milestone, but the path from recorded narration to a polished submission on ACX (Audiobook Creation Exchange) requires precision and an eye for detail. ACX has strict technical and quality standards that every title must meet before it can be listed on Audible, Amazon, and iTunes. Even minor missteps—like a slightly off bit rate or a background noise spike—can result in a “require corrections” status, delaying your launch by days or weeks.

This comprehensive guide walks you through every step of the finalization process, from preparing audio files to submitting your complete package. Whether you’re a narrator, rights holder, or a hybrid producer, following these instructions will help you avoid common pitfalls and get your audiobook approved on the first attempt.

1. Pre‑Production Preparation: Setting Up for Success

Before you even press record, establishing a consistent recording environment and workflow saves countless hours of editing later. ACX’s quality standards are non‑negotiable, so the foundation you build in pre‑production directly impacts your approval rate.

Choose a Suitable Recording Space

Your room’s acoustics matter more than your microphone. A untreated room with hard surfaces creates echo and reverb that is difficult to remove without degrading voice quality. Aim for a space with carpet, curtains, and soft furniture. If you lack a quiet room, invest in a portable vocal booth (e.g., a PVC‑frame booth with acoustic blankets) or build a DIY fort using moving blankets. Test your space by recording 30 seconds of silence and analyzing the noise floor in your DAW—it should be below -60 dBFS.

Select the Right Microphone and Technique

A large‑diaphragm condenser microphone (like the Audio‑Technica AT2020 or Rode NT1) is a common choice for voice‑over, but a dynamic microphone (Shure SM7B or Electro‑Voice RE20) can be better if your room is not fully treated. Regardless of mic type, maintain a consistent distance of 6–12 inches from the capsule. Use a pop filter to reduce plosives. Record at a moderate gain level—peaking around -6 dB to -3 dB—to give yourself headroom for editing. Avoid clipping at all costs; a clipped waveform cannot be repaired cleanly.

Establish a Consistent Recording Workflow

  • Warm up your voice for 5–10 minutes before each session.
  • Record in short takes (10–15 minutes) to avoid fatigue and to make punch‑ins easier.
  • Use a consistent microphone position and recording level throughout.
  • Label each file with the chapter number and date in your DAW session.
  • After each session, back up raw files immediately to an external drive or cloud storage.

Investing time in pre‑production prevents the need to re‑record entire chapters later.

2. Preparing Your Audio Files

ACX mandates specific technical specifications to ensure consistent playback across all devices. Before you even think about uploading, verify that every single file adheres to these requirements.

File Format and Bit Rate

  • Format: Only MP3 files are accepted. Do not submit WAV, FLAC, or any other container.
  • Minimum Bit Rate: 192 kbps or higher. Many professionals use 256 kbps for a balance of quality and file size. For exceptionally complex recordings (e.g., music, multiple voices) consider 320 kbps.
  • Maximum Bit Rate: Keep it under 320 kbps to avoid excessive file sizes that may trigger upload errors.

Sample Rate

ACX requires a sample rate of 44,100 Hz (44.1 kHz). This is the standard for CD-quality audio. If your source files are recorded at 48 kHz (common for video production), convert them down using a sample rate converter that applies proper anti-aliasing to prevent distortion. Audacity’s default sample rate conversion is adequate; for higher‑end results, use RX Sample Rate or similar tools.

Channels: Mono vs. Stereo

While ACX accepts both mono and stereo, mono is strongly preferred for spoken-word audiobooks. Stereo files double the file size with no benefit for a single narrator. In fact, presenting a mono narration as stereo can cause phasing issues if the listener’s playback system hard‑pans both channels. Unless your audiobook includes stereo‑sound effects or music that relies on panning, export everything as mono.

File Naming Conventions

ACX does not prescribe a rigid naming system, but consistency is crucial. Use a format that sorts correctly and includes the part or chapter number. For example:

  • TitleOfBook_Part01.mp3
  • AuthorName_Chapter5.mp3
  • ABID_12345_Track01.mp3 (if you have an Audible ID)

Do not use special characters or spaces that might break on upload. Underscores and hyphens are safe. Avoid dates or version numbers in the filename (e.g., Ch3_v2.mp3) as they can confuse the ordering system.

File Size Limits

ACX imposes a per‑file upload limit of 5 GB and a total project limit of 10 GB. A typical 10‑hour audiobook at 192 kbps mono is about 800 MB, so you’re safe—but always check total size before uploading. To estimate: file size (MB) = (bitrate in kbps) × (duration in seconds) / 8 / 1000.

3. Editing and Quality Control

Technical specs alone won’t get you approved. ACX has a strict audio quality standard that must be met throughout the entire recording. The review team listens for six criteria: noise floor, volume consistency, pacing, breath control, artefacts, and intelligibility. Each of these areas requires careful attention during post‑production.

Noise Reduction and Denoising

Your finished audio must have a noise floor of -60 dB or lower (relative to the RMS level of the speech). Use a spectral analyzer to identify constant background hums (fans, air conditioning, electrical noise). Apply a narrow‑band EQ notch or a denoiser like iZotope RX, Accusonus ERA, or even a free tool like Audacity’s Noise Reduction. Be careful not to over‑process: aggressive denoising can create “watery” or robotic artifacts that ACX will flag. Always audition the processed audio in context—what sounds clean in isolation may sound unnatural in a chapter.

Volume Normalization

ACX expects a consistent average loudness of -23 dB LUFS (plus or minus 2 dB). Peak levels should not exceed -3 dBFS (or -6 dBFS if you want extra headroom). Use a loudness normalization plugin or the Loudness Normalization effect in Audacity with target integrated -23 LUFS. Do not rely on simple peak‑normalization; LUFS is the standard for broadcast and streaming and is what ACX uses. Batch processing all chapters with the same target ensures consistent perceived loudness across your book.

Editing Out Mistakes and Artifacts

Listen through the entire recording on good-quality headphones. Remove:

  • Pops and clicks (microphone bumps, mouth clicks)
  • Overly loud breaths (some breath is natural—don’t remove all of it; reduce to about -24 dB relative to speech)
  • Plosive bursts on “P” and “B” sounds (de‑ess and apply a high‑pass filter below 80 Hz)
  • Sibilance (hissing “S” sounds) using a de‑esser
  • Unexpected room noises (chair creaks, page turns, clothing rustle)
  • Re‑recorded lines that don’t match the ambient sound of surrounding sections (either trim or add subtle crossfades)

Pacing and Silence Lengths

ACX has guidelines for silence within chapters:

  • Between sentences: natural speech rhythm; no fixed rule
  • Between paragraphs: 1–2 seconds
  • At the beginning of a chapter: up to 1 second of silence
  • At the end of a chapter: up to 1 second of silence (do not add long fades)

If you use silence to indicate scene breaks, keep it consistent (commonly 3–5 seconds). Overly long silences (more than 10 seconds) may cause the listener to think playback stopped. Also ensure that chapter transitions do not overlap—the final silence of one file and the initial silence of the next should combine to a natural pause.

Quality Check Tools

Use ACX’s own Audio Checker (free desktop app) to validate your files before uploading. It tests peak level, RMS, noise floor, and sampling rate. Even if you’re confident, run every file through the checker—it catches issues your ears might miss. Additionally, the Audible Quality Check Guide provides a detailed listening protocol.

Alternatively, plugins like Auphonic can automate loudness and noise reduction, saving hours of manual editing. Auphonic’s web service or desktop app applies intelligent algorithms to meet ACX targets.

4. Mastering the Final Mix

After editing and normalization, a final master bus process can ensure consistency across all chapters. Apply a gentle limiter with a ceiling of -3 dBFS to catch any stray peaks. Use a multiband compressor to even out frequency imbalances—for example, a slight dip around 200 Hz reduces muddiness, while a gentle boost at 4 kHz adds clarity without harshness. Avoid aggressive EQ that alters the natural timbre of your voice. A high‑pass filter at 80 Hz removes subsonic rumbles. Export each chapter at the identical settings to maintain a seamless listening experience.

5. Creating the Cover Image

Your audiobook cover is the first thing a potential listener sees. ACX enforces strict specifications to ensure consistent display across retailers.

Dimensions and Resolution

  • Minimum dimensions: 2400 × 2400 pixels
  • Maximum dimensions: 3000 × 3000 pixels (some retailers accept larger, but stick to 2400‑3000)
  • Resolution: 300 dpi
  • Aspect ratio: 1:1 (square)

Color Space and Format

Use RGB color mode, not CMYK (which is for print). Upload as JPEG or PNG. JPEG is preferred for photographic covers; PNG for text-heavy or crisp graphic designs. Do not include a bleed area or trim marks—the image is used as‑is.

File Size Limits

The cover file must be smaller than 10 MB. A 2400×2400 JPEG at quality 80% usually comes in under 3 MB. If you need to reduce size, lower JPEG quality slightly, never scale down below 2400 px.

Design Tips for Approval

  • Do not include Amazon, Audible, or iTunes logos on the cover—they are added automatically.
  • Avoid tiny text that becomes unreadable when rendered as a thumbnail (200 px).
  • Use a high-contrast title for legibility on mobile screens.
  • If you are using a photo of a narrator or celebrity, ensure you have a signed model release and proper licensing.
  • Check the official ACX cover image requirements for the latest details.

6. Writing the Book Description and Metadata

Metadata gets your audiobook found in search results. Inaccurate or missing metadata can seriously limit discoverability.

Title and Subtitle

Enter exactly as it appears on your cover. Do not add “(Audiobook)” unless it’s part of the official title. Avoid all caps or excessive punctuation.

Author and Narrator

Both fields are required. If you are the author and narrator, list yourself in both with the same spelling. Add a short bio (50–150 characters) that highlights relevant experience.
Example Author Bio: “Jane Doe is a bestselling fantasy author with over 500,000 copies sold.”
Example Narrator Bio: “John Smith is a classically trained actor and a multiple Audiobook of the Year finalist.”

Book Description (Synopsis)

This is the most important marketing copy. Write 150–300 words that hook a listener. Structure it like a traditional back‑cover blurb: introduce the protagonist, the central conflict, and a hint of the stakes. Avoid spoilers. Use natural language—no “This audiobook will…” fluff. Tip: If your book has positive reviews, weave a short pull quote into the description (with permission). Research keywords in your genre and incorporate them naturally to improve search ranking.

Keywords and Categories

ACX allows up to three categories. Choose the most specific ones (e.g., “Fiction → Fantasy → Epic” rather than just “Fantasy”). For keywords, you get seven phrases. Use a mix of:

  • Genre variations (“dark fantasy,” “sword and sorcery”)
  • Compelling tags (“time travel romance,” “dystopian thriller”)
  • Series name if applicable (“The Ember Series Book 2”)
  • Listener hooks (“binge‑worthy narration,” “gripping mystery”)

Run your keywords through Amazon’s autocomplete tool to see what real users search for. Avoid generic terms like “audiobook,” which waste keyword slots.

Series Information

If your audiobook is part of a series, enter the series name and book number. This enables automatic “Series” linking on Amazon and Audible, which boosts cross‑sales.

7. Uploading to ACX

With all files ready, it’s time to upload. Follow these steps carefully.

Log In and Create a New Title

Go to acx.com and log in to your account. Click “Add New Title.” You’ll be asked whether you already have the rights or are looking for a narrator. Choose accordingly. If you’re the rights holder, you’ll proceed to fill in metadata.

Upload Audio Files

On the “Audio” tab, you can upload files individually or in bulk. ACX will automatically re‑order if your filenames are numbered. If the sequence is wrong, drag and drop to reorder.

  • Each file should correspond to a chapter or part. Do not combine multiple chapters into one file unless they are very short.
  • After uploading, ACX runs a preliminary validation (format, sampling rate, bit rate, loudness). Warnings will appear for any non‑compliance. Do not proceed until every file shows a green check.

Upload Cover Image

On the “Cover” tab, drag your 2400×2400 JPEG/PNG. ACX will generate a preview. Zoom in to ensure text is sharp and no important elements are cut off.

Fill Out Metadata

The “Details” tab includes all the fields described in Section 5. Be thorough. Missing required fields will block submission.

Choose Distribution

ACX offers two distribution options:

  • Non‑Exclusive: You can sell the audiobook elsewhere. Royalty is 25% for sales on Audible/Amazon/iTunes.
  • Exclusive (ACX Select): Higher royalty (40% on Audible/Amazon, 25% on iTunes) but you cannot sell the audiobook elsewhere for the duration of exclusivity (usually 2 years).

Weigh this decision carefully. If you have a large email list or other channels, non‑exclusive may be better. If you rely solely on Audible, exclusivity often yields higher royalties. Also consider ACX Select’s promotional tools (like free codes and Countdown Deals) which are available only to exclusive titles.

8. Final Quality Assurance (QA) Checklist

Before hitting the “Submit for Review” button, run through this checklist methodically.

Audio

  • All files are MP3, 192–320 kbps, 44.1 kHz, mono (or stereo if necessary)
  • Average loudness touches -23 LUFS (±2 dB)
  • Peak levels never exceed -3 dBFS
  • Noise floor is -60 dB or lower relative to RMS
  • No audible artifacts, clicks, pops, or unrepaired mouth sounds
  • Pacing is natural; silent gaps are uniform
  • File names are consistent and sort correctly
  • Every file passes ACX Audio Checker without warnings

Cover

  • Dimensions: 2400×2400 minimum
  • Color mode: RGB
  • File size under 10 MB
  • No third‑party logos
  • Readable thumbnail

Metadata

  • Title, author, and narrator match exactly the cover and your rights
  • Description is compelling and accurate
  • Categories and keywords are relevant and specific
  • Bios for author and narrator are filled in
  • Distribution option selected

Final Glitch‑Hunt

Listen to the first 5–10 minutes of your audiobook inside the ACX preview player. This emulates how the file will sound after encoding. Click around to verify chapter breaks and that no overlapping audio occurs at boundaries. If possible, have a second listener (trusted beta ear) do the same check—fresh ears catch distracting sounds you might have tuned out.

9. Submission and Review Process

Once you submit, ACX will put your audiobook in a queue. Review times vary—typically 10–14 business days, but can be longer during peak seasons (holiday months).

Possible Review Outcomes

  1. Approved: Congratulations! Your audiobook moves to distribution within a few days.
  2. Require Corrections: The review team will list specific issues. Common reasons: background noise, inconsistent volume, clipped peaks, incorrect metadata, or cover too small.
    Read the notes carefully, fix each issue, and re‑upload the updated files. There is no limit on correction cycles, but each resubmission goes back into the queue. If multiple files need correction, fix them all at once to avoid successive wait times.
  3. Rejected: This is rare. It means the title fundamentally doesn’t meet standards (e.g., rights issues, inappropriate content). ACX will provide a reason and possible appeal route.

After Approval

Your audiobook will appear on Audible.com within 3–5 business days, then on Amazon and iTunes shortly after. You’ll receive an email with a sales link. Promote that link to your audience via your website, social media, newsletter, and any other channels. Consider running a promotional campaign using your free promo codes (if you opted for exclusivity) to generate early reviews and boost rankings.

10. Common Pitfalls and How to Avoid Them

Even experienced producers stumble. Here are the top five reasons ACX submissions get bounced back:

  • Background noise too high: Usually from a noisy room or insufficient soundproofing. Invest in a portable vocal booth or treat your recording space. Even after noise reduction, residual ambient sound can push the floor above -60 dB.
  • Inconsistent loudness across chapters: Each file must hit -23 LUFS independently. Batch‑process with a loudness normalizer like Auphonic or Audacity’s plugin. Do not rely on manual gain adjustments alone.
  • Cover image too small or wrong color space: Use a proper image editor (Photoshop, GIMP, Canva Pro) and check the dimensions before upload. A common mistake is accidentally exporting at 72 dpi instead of 300 dpi—this still shows 2400×2400 pixels but can cause rejection.
  • Incorrect sample rate: Double‑check your export settings. A stray 48 kHz file will fail validation. Set your DAW’s export settings to 44.1 kHz and verify with the ACX Audio Checker.
  • Missing metadata fields: Fill in every required box. Leaving narrator bio blank is a common oversight. Also ensure that the author name matches legal rights—using a pseudonym is fine, but must be consistent across the cover and metadata.

11. Tools and Resources

Leverage these tools to streamline your workflow:

  • ACX Audio Submission Requirements – The official specs page with all technical guidelines.
  • Audacity – Free, open‑source audio editor. Pair with the Loudness Normalization plug‑in (requires FFmpeg) to meet LUFS targets.
  • Auphonic – Automated audio post-production tool that levels loudness, reduces noise, and applies EQ. The web version offers a free tier up to 6 hours per month.
  • Cambridge Audio Mastering Tools – Online LUFS meter and loudness checker for quick validation.
  • Paint.NET – Free image editor for cover resizing and simple retouching. For advanced design, consider GIMP or Canva Pro.
  • Audible Quality Check Guide – Additional listening tips and a downloadable checklist from the parent platform.

12. Conclusion

Finalizing your audiobook for ACX submission is a meticulous process, but it’s the last hurdle before your hard work reaches listeners worldwide. By adhering to the technical specs, polishing your audio to ACX’s quality standards, and crafting compelling metadata, you dramatically increase the odds of a first‑time approval. Take your time with the final QA checklist—one extra hour of proofing can save you two weeks of back‑and‑forth corrections. Once approved, your audiobook will be live on the world’s largest audiobook platform, ready to entertain, inform, and inspire.

With these steps, you’re equipped to submit with confidence. Good luck, and happy narrating!