Frequently Asked Questions

ChapterPass is a web tool that masters your audiobook chapter files for ACX submission[1]. You upload your recorded chapters, and the engine adjusts loudness, limits peaks, manages noise floor, converts to the required format, and pads silence at the start and end of each file. Every output file is verified against ACX's measurable technical specs before you can download it. Your files never leave your browser. All processing runs locally.

ChapterPass accepts WAV, MP3, FLAC, AIFF, and M4A files. For best results, upload uncompressed WAV or lossless FLAC files. 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 in 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.

Your first file is completely free. No account, no credit card, no signup. After that, pricing is €0.01 per second of audio, roughly €36 ($40) per finished hour. You see the exact price before you pay.

Your first file is free, with no account or payment needed. After that, pricing is €0.01 per second, roughly €36 ($40) per finished hour. A typical 30-minute chapter costs about €18 ($20). You'll see the exact price before you pay. No subscriptions, no hidden fees.

The two services cover different ground. ChapterPass handles technical mastering: loudness, peaks, noise floor, format, and silence padding. A human editor also handles content cleanup like clicks, pops, mouth noise, room echo, and pacing. If your source audio is already clean, ChapterPass is the faster and cheaper path to ACX-ready files. If your recordings need content-level editing, a human editor is still worth the investment. Many narrators use both: a human editor for the content pass, then ChapterPass for the final technical mastering.

Processing time depends on chapter length and your computer. A typical chapter processes in a few minutes. Longer chapters (60+ minutes) may take longer. 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. Browsers slow down background tabs to save power, so switching away can make processing take much longer. Close tabs and apps you are not using, since each one competes for memory. And plug in your laptop if you are on battery, because laptops reduce processor speed on battery to save power.

No. All processing runs locally in your browser. Your audio files are never uploaded to a server, never stored remotely, and never accessible to anyone but you. ChapterPass works offline once the page is loaded.

No. ChapterPass handles the measurable technical specs: loudness, peaks, noise floor[1], format, and silence. But ACX also has a human quality review that listens for things like clicks, pops, mouth noise, echo, pacing consistency, and whether your narration matches the manuscript. If your recording has audio quality issues, those will still cause rejection regardless of what ChapterPass does to the technical numbers. ChapterPass masters the audio. It does not fix recording problems.

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 artifacts needs to happen in your recording software before you upload to ChapterPass.

No. ACX requires[1] 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. If you start with a problem recording, the problems will still be there after processing.

ACX checks two things. First, measurable technical specs[1]: loudness, peaks, noise floor, format, sample rate, channels, and silence padding. ChapterPass handles all of these. Second, a human review. ACX's QA team listens to your audio for recording quality issues like clicks, pops, echo, inconsistent narration, missing credits, and content accuracy. Both checks need to pass for your audiobook to be accepted.

If your files passed ChapterPass verification but were still rejected, the issue is almost certainly in ACX's human review, not the technical specs. Common reasons include audible clicks or pops, mouth noise, room echo, inconsistent tone or pacing between chapters, missing opening or closing credits, or narration that doesn't match the manuscript. Check your rejection notice for specifics and address those in your recording or editing software.

Not for the technical mastering. That's what ChapterPass replaces. But you will need some way to record and edit your narration (remove mistakes, clean up audio, add credits). That could be a DAW, or it could be a simpler audio editor. Once your edited recording is ready, ChapterPass handles the mastering step.

ACX requires each chapter to have an RMS loudness between -23 and -18 dBFS[1]. RMS (Root Mean Square) measures the average loudness of your audio over time. If your RMS is too low, the audiobook sounds too quiet. If it's too high, it sounds uncomfortably loud and leaves no headroom. ChapterPass measures your audio and adjusts gain to land within this range automatically.

ACX requires the noise floor to be below -60 dBFS[1]. The noise floor is the level of background sound present during silent passages: room tone, mic hiss, computer fan noise. If your noise floor is above -60 dBFS, ACX will reject the file. ChapterPass manages noise in silent sections to keep the floor below the threshold while preserving a natural sound.

ACX requires mono MP3 files at 44100 Hz sample rate with a constant bit rate (CBR) of 192 kbps or higher.[1] Stereo files will be rejected. Variable bit rate (VBR) MP3s will be rejected. WAV or FLAC files need to be converted to MP3 before submission. ChapterPass converts any supported input format (WAV, MP3, FLAC, AIFF, M4A) to this exact specification.

No. ChapterPass requires a modern desktop or laptop browser. The audio processing engine needs more memory and CPU than mobile browsers can reliably provide. Use Chrome, Firefox, Safari, or Edge on a computer. A typical chapter processes in a few minutes on a modern laptop.