Frequently Asked Questions

No. All processing runs locally in your browser. Your files are never uploaded to a server, never stored remotely, and never accessible to anyone but you. If you are working under a publisher non-disclosure agreement or on an unreleased manuscript, your audio does not leave your device.

ChapterPass is a browser-based tool that masters your audiobook files for distribution. You upload your recorded chapters and the engine masters every chapter to ACX spec: loudness, peaks, noise floor, format, and silence padding. Every output is verified against ACX's measurable technical specs before you can download it. Your files never leave your browser. All processing runs locally on your device.

ChapterPass accepts WAV, MP3, FLAC, AIFF, and M4A files. For best results, upload uncompressed WAV or lossless FLAC. If you upload an MP3 below 192 kbps, ChapterPass will flag it with a warning. The file will still process, but the output quality may suffer since the engine is working with already-degraded audio. The output is always mono MP3 at 192 kbps CBR, the format ACX requires.

Yes. Your first file is completely free. No account, no payment info, no strings. Upload a chapter, process it, and check the results. If you're happy, pay to process the rest.

A typical chapter processes in a few minutes. Chapters over 60 minutes take proportionally more time. The engine runs entirely in your browser, so speed depends on your device. You can upload multiple chapters at once and each will be processed in sequence.

Three things make the biggest difference. Keep the ChapterPass tab visible while your files are processing, because browsers slow down background tabs to save power. Close tabs and apps you are not using, since each one competes for memory. Plug in your laptop. On battery, processors throttle down to conserve power.

ChapterPass runs on desktop or laptop browsers. Chrome, Firefox, Safari, or Edge on a computer. Mobile browsers can't reliably provide the memory and CPU the engine needs.

Not for the mastering step; that's 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. Audacity is free and handles all of it. Once your edited recording is ready, ChapterPass handles the mastering step. See Audacity audiobook mastering for the exact effect chain.

Yes. Master to ACX spec and the output also meets the requirements for INaudio (formerly Findaway Voices), Authors Republic, and Google Play Books. The cross-platform comparison table shows the exact overlaps.

ChapterPass is deterministic, not AI. Same input, same output, every time. No machine learning, no neural networks, no generative models. It's the same type of signal chain hardware limiters and mastering chains have used for decades, automated and verified against ACX specs.

ChapterPass handles the measurable technical specs: loudness, peaks, noise floor, format, and silence. ACX also runs a human quality review for clicks, pops, mouth noise, echo, pacing, and manuscript accuracy, which no mastering tool can pass for you. Recording quality issues will still cause rejection regardless of what ChapterPass does to the technical numbers. For the full decision tree, see fix ACX rejection.

ChapterPass handles loudness, peaks, noise floor in silent sections, and format conversion. It does not edit the content of your narration. Clicks, pops, mouth noise, and other recording artefacts are best removed in your recording software before you upload. See what ChapterPass does for the full scope.

No. ACX requires opening credits (title, author, narrator) and closing credits at the end of your audiobook. You need to record these yourself and include them as separate chapter files. ChapterPass processes whatever files you give it. It does not create new content.

Yes. ChapterPass handles the technical mastering, but your recording quality is your responsibility. Before uploading, make sure your audio is clean: no background noise louder than room tone, no clicks or pops, no echo or reverb, and consistent narration quality across all chapters. If you start with a good recording, ChapterPass will produce a great result. See audiobook noise floor guide for the most common recording quality issue.

The issue is almost certainly in ACX's human quality review, not the technical specs. Common reasons: audible clicks or pops, mouth noise, room echo, inconsistent tone between chapters, missing credits, or narration that does not match the manuscript. Check your rejection email for specifics. For a step-by-step fix guide, see fix ACX rejection.