Automatic ACX
Audiobook Mastering
for Narrators
ChapterPass is an automated processing tool that formats your voice recordings to meet strict Audible technical standards.
Open on your computer
Mastering runs entirely in your browser and needs the processing power of a full computer.
Drop your chapter files here
or browse files
Accepted formats: WAV, MP3, FLAC, AIFF, M4A. Maximum duration 120 minutes.
How it works
Upload Your Chapters
Drop your finished recordings into ChapterPass. No account, no plugins, no prep. Everything runs locally, so your files never leave your browser.
Start Processing
A 9-step mastering pipeline filters, levels, limits, and shapes your noise floor. Every file is then verified against the 8 ACX technical specs: RMS loudness, true peak, noise floor, sample rate, channel count, bit rate, head silence, and tail silence.
Download Your Masters
Download your ACX technical-spec files in minutes, with a full compliance report for every chapter. Your first chapter is free, so you can hear it before paying.
Audiobook submission, sorted
You bring the performance. ChapterPass handles the technical specs that platforms like ACX require. Built for human narrators.
You bring
- Clean recording
- Consistent narration
- Opening & closing credits
- One chapter per file
We handle
- Loudness
- Peak control
- Background noise
- Head & tail silence padding
- Compliant MP3 export
- Compliance report
Know the cost before you start.
Your first file is free. No account, no card, no catch.
For a 10-hour audiobook, four ways to get ACX technical-spec files.
| Mastering Method | Estimated Cost | Time | Trade-offs |
|---|---|---|---|
| Human mastering engineer | $700 to $1,200 | 3 to 7 days | IP exposure, communication overhead |
| Fiverr freelancer | $100 to $300 | 1 to 3 days | Variable quality, IP exposure |
| Manual in Audacity | Free | 2 to 10+ hours | Steep learning curve, high rejection risk |
| ChapterPass (10+ tier) | $180 | ~5 minutes | Private, deterministic, report-backed |
Why narrators choose ChapterPass
Saved on average vs. the alternatives
Lower cost than studio mastering
Files shared. Your audio goes nowhere.
Savings and cost figures estimated from the comparison above.
FAQ
Do my files leave my computer?
No. All processing runs locally in your browser via WebAssembly. Your audio files are never uploaded to a server, never stored remotely, and never accessible to anyone but you.
How much does ChapterPass cost?
Your first file is free, no account or payment needed. After that, pricing depends on total audio length: under 5 hours costs $36 per finished hour, 5 to 10 hours costs $27 per finished hour, and 10+ hours costs $18 per finished hour. You see the exact price before you pay. No subscriptions, no hidden fees.
Does ChapterPass guarantee my audiobook will pass platform quality review?
No. ChapterPass handles the measurable technical specs: loudness, peaks, noise floor, format, and silence. ACX also runs a human quality review that listens for clicks, pops, mouth noise, echo, pacing, and manuscript accuracy. Recording quality issues will still cause rejection regardless of what ChapterPass does to the technical numbers.
Does ChapterPass remove clicks, pops, or mouth noise?
No. ChapterPass adjusts loudness, limits peaks, manages noise floor in silent sections, and converts to the right format. It does not edit the content of your narration. Removing clicks, pops, mouth noise, or other recording artefacts needs to happen in your recording software before you upload.
Do I need a DAW to use ChapterPass?
Not for the technical mastering. That is what ChapterPass replaces. You will still need a way to record and edit your narration (remove mistakes, clean up audio, add credits). That could be a DAW or a simpler audio editor like Audacity. Once your edited recording is ready, ChapterPass handles the mastering step.
Should I use Audacity, hire a mastering engineer, or use ChapterPass?
All three routes produce distribution-ready files. Audacity is free and gives you full control, but you configure four effects, run a macro, and verify results manually. Hiring a mastering engineer is hands-off: you send files, you receive mastered files, typically hundreds of dollars per finished hour. ChapterPass sits between: drop a file in, get a verified file out, $18 to $36 per finished hour, first file free, files stay on your device.
Latest releases
Practical guides to help you master, format, and deliver your audiobook with confidence.
ACX Audio Specs + Fix Your File Free (2026)
May 29, 2026
The exact ACX targets for RMS, peak and noise floor, plus a free in-browser way to master your file so it passes on the first try.
ACX Rejected Your Audiobook? Fix Every Issue
May 20, 2026
From ACX rejection email to fix, without uploading your file. Loudness, noise floor, true peak, format. Files stay in your browser.
Audacity Audiobook Mastering: Full ACX Workflow
May 20, 2026
The exact Audacity effect chain for mastering audiobooks to ACX spec. Noise reduction, compressor, normalise, limiter, and the batch macro.
Browse the full library of ACX audiobook mastering guides, or read the mastering tool comparison.