For self-published audiobook narrators
ACX sent your audio back? Fix it in minutes.
Drop in your chapter files. ChapterReady sets the loudness, peaks, noise floor and room tone, saves each chapter as the MP3 ACX asks for, then measures it again so you can see it passes before you upload.
| Before | After | ACX needs | |
|---|---|---|---|
| Loudness | -26.9 dB | -20.2 dB | -23 to -18 |
| Peaks | -11.2 dB | -4.6 dB | -3 or lower |
| Noise floor | -56.2 dB | -72.4 dB | -60 or lower |
| Start tone | 4.21 s | 0.77 s | 0.5 to 1 s |
| End tone | 1.08 s | 2.53 s | 1 to 5 s |
| Format | WAV stereo | MP3 192k CBR | MP3 192k+ CBR |
Why ACX sends files back
Every file you upload is measured against a list of technical rules, and a file that misses one is returned. Loudness and noise are the hardest to get right in a home studio.
- RMS between -23 and -18 dBRecordings made with safe microphone levels often come in below -23 dB.
- Peaks at -3 dB or lowerTurning a quiet file up pushes loud words over this line.
- Noise floor at -60 dB or lowerFridges, laptop fans, traffic and room echo all count against you.
- Room tone at both ends0.5 to 1 second at the start of each file and 1 to 5 seconds at the end.
- 192 kbps CBR MP3 at 44.1 kHzVariable bit rate and 48 kHz files are rejected.
- 120 minutes per file at mostOne chapter per file, and every file in mono or every file in stereo.
Fixing this yourself means learning noise profiles, compressors, limiters and Audacity macros, then repeating it for every chapter. Every change to one setting moves the others.
How it works
Drop in your chapters
WAV, MP3, FLAC, M4A or AIFF. Add a whole book at once and they're processed one after another.
Wait a minute or two
Noise is reduced, levels are set and room tone is trimmed or added. A 45-minute chapter took under two minutes in our tests.
Check the report, then download
See the before and after numbers for each ACX rule, listen in the page, and download each MP3 or the whole book as a ZIP.
Cheaper and faster than hiring on Fiverr
The usual fix is to hire a freelancer to master your files. That means an order per batch, a day or more of waiting, and messages back and forth when a chapter still fails. ChapterReady does the same technical job in one place while you wait, and shows you the numbers.
| ChapterReady | A mastering gig on Fiverr | |
|---|---|---|
| A 10-hour book | £30 for the whole book | About £69 for basic ACX mastering, or £250 and up with hand editing |
| Turnaround | Minutes, while you watch | 1 to 3 days per order, plus time for revisions |
| Proof it passes | Every finished MP3 is measured again and you see the numbers | Depends on the seller |
| Re-recorded a chapter | Drop it in again while your pass is active | Message the seller or place a new order |
| Your recordings | Stay on your computer | Uploaded to someone you've never met |
| If it still fails | Our team fixes it, or you get a full refund within 30 days | Revisions, then Fiverr's dispute process |
Fiverr prices are from a popular, well-reviewed ACX mastering gig in September 2026: £6.89 per finished hour for basic mastering including Fiverr's service fee, and £23.56 per finished hour before fees for hand editing. Hand editing does more than ChapterReady: a person removes breaths and mouth clicks by ear. If your files only need to pass ACX's technical check, you don't need to pay for that.
Your recording never leaves your computer
All the processing happens inside your browser tab. Nothing is uploaded, so an unreleased book stays unreleased. There's no account to create and no file size to pay for.
What ChapterReady fixes
- Loudness set to about -20 dB RMS
- Peaks held under -3 dB, with a margin for MP3 encoding
- Background hiss, hum and fan noise reduced by up to 24 dB
- Rumble below 80 Hz removed
- 0.75 seconds of room tone at the start, 2.5 seconds at the end
- Stereo turned into mono so every file matches
- Saved as 192 kbps constant bit rate MP3 at 44.1 kHz
What it can't fix
After the technical check, a person at ACX listens to your files. They listen for mouth clicks, plosives, edits you can hear, misread lines and chapters that sound different from each other. Software can't fix a performance.
ChapterReady also can't repair clipping, where the recording was too loud and distorted. A recording that is mostly noise will sound watery after heavy noise reduction, and the report warns you when that happens.
Listen to every fixed file before you upload it.
One price per book
Check as many files as you like for free and see every number first. Buy a book pass when you're happy with the result.
Book pass
£30 per book
- Every chapter of one audiobook, up to 15 hours of finished audio (about 135,000 words)
- 90 days to finish and re-run as many times as you need
- Download each MP3 or the whole book as a ZIP
- No subscription and no account
- Card payment by Stripe
It passes, or you get your money back
If a file you fixed with ChapterReady still fails ACX's technical check, send it to us and our team will fix it. If we can't, we refund your book pass in full. Claim within 30 days of buying. Full terms.
Questions
Will my book definitely pass ACX?
No tool can promise that, because a person at ACX also listens to every file. ChapterReady makes sure each measurable rule is met and shows you the numbers from the finished MP3, so the technical check isn't the reason your book comes back.
Is my audio uploaded anywhere?
No. The processing runs in your browser using your computer, and your files never reach our servers. The only exception is if you send a file to our team to fix under the refund promise. We use it only for that and delete it within 30 days.
What counts as one book?
A book pass covers up to 15 hours of finished audio, about 135,000 words of narration. That's longer than most novels. Each chapter you download uses time equal to its length, and downloading the same file again is free. Checking files and listening to them in the page is always free.
What does the refund promise cover?
If a file you fixed with ChapterReady fails ACX's technical requirements (loudness, peaks, noise floor, room tone or format), email it to us with ACX's message. Our team will fix it. If we can't, we refund your book pass in full, as long as you ask within 30 days of buying it. It doesn't cover ACX's listening review of the performance, such as misread lines or mouth noise.
What if my book is longer, or I need more time?
Buy a second book pass. It adds another 15 hours to what you have left and gives you 90 days from that purchase. Time left on a pass when it expires isn't carried over.
What if my recording is very noisy?
ChapterReady reduces noise by up to 24 dB and tells you when it had to work hard. If noise is close to the level of your voice, the result can sound watery. Re-recording in a quieter space is the only real fix for that.
Can I use it on my phone?
Use a laptop or desktop. Long chapters need a lot of memory while they're processed, and phones run out. It works in current versions of Chrome, Edge, Firefox and Safari.
Do I get my files back as mono?
Yes. ACX accepts mono or stereo as long as every file matches, and mono is the normal choice for narration. It also keeps your files smaller.
Is ChapterReady part of ACX or Audible?
No. ChapterReady is made by NimblePanda Ltd, an independent UK company. It isn't affiliated with or endorsed by ACX, Audible or Amazon.
I have a question that isn't here
Email hello@nimblepanda.co.uk and a person will reply.
See where your chapters stand
Checking is free and takes a couple of minutes per chapter. You only pay if you want the fixed files.