Automatic audiobook
mastering in minutes
chapterpass formats your voice recordings to meet Audible’s strict ACX technical standards. Drop a file in, get a submission-ready file out.
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.
Example output
Every file comes back with a report
This is the same report you get for every file: each spec measured, with the ACX target beside it. Targets sourced from ACX: Audio Submission Requirements. For what each number means, read the ACX audio specs guide.
How it works
Three steps, all in your browser
Upload your chapters
Drop your edited recordings straight into this browser tab. No account, no install, nothing to configure.
Mastered on your device
chapterpass levels loudness, controls peaks, manages the noise floor, sets the right format, pads the silences, and masters every file to the ACX spec.
Download your masters
Save ACX-ready files in minutes, each with its own compliance report. Your first chapter is free, so you can hear it before you pay.
Private by design
Runs in your browser
All mastering happens locally in WebAssembly, on your own machine.
Never uploaded
Your recordings stay in this tab. Nothing is ever sent to a server.
Nothing stored
We keep no copy of your audio. Close the tab and nothing of yours remains.
Who does what
Audiobook submission, sorted
We handle
6 checks- Loudness
- Peak control
- Noise floor
- Head & tail silence padding
- Compliant MP3 export
- Compliance report
You bring
4 inputs- Clean recording
- Consistent narration
- Opening & closing credits
- One chapter per file
Pricing
Know the cost before you start
Under 5 hrs
$36/ finished hr
5-10 hrs
$27/ finished hr
10+ hrs
Best rate$18/ finished hr
A 10-hour audiobook, three ways to get ACX-ready
IP exposure, communication overhead
Steep learning curve
Private, deterministic, report-backed
Time saved
Budget saved
Your first file
Built for narrators
“This. Is. Brilliant. This takes QC and mastering from where I started at 5 hours per 1 hour of audio to maybe 2 total for a 10 hour book. It’s mind blowing. Thanks for creating chapterpass!!!”
Laura G.
Multiple Earphones Award Winner · Audie Award Finalist · SOVAS Voice Arts Winner
Guides
Guides to get you ACX-ready
ACX Audio Submission Requirements: RMS, Peak, Noise Floor
ACX audio submission requirements in full: RMS -23 to -18 dBFS, peak below -3 dBFS, noise floor below -60 dBFS. Master your file free in your browser.
Read guide →1 of 3GuideACX Rejected Your Audiobook? Fix Every Issue
From ACX rejection email to fix, without uploading your file. Loudness, noise floor, true peak, format. Files stay in your browser.
Read guide →2 of 3GuideAudacity Audiobook Mastering: Full ACX Workflow
The exact Audacity effect chain for mastering audiobooks to ACX spec. Noise reduction, compressor, normalise, limiter, and the batch macro.
Read guide →3 of 3Browse the full library of ACX audiobook mastering guides, read the mastering tool comparison, or see where your file stands with the free ACX check.
FAQ
Questions, answered
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.
More questions? The full FAQ page has the complete list of answers.
Start free
Master your first file free
Drop a chapter in, see the report, download a submission-ready file. No account, no card.