# Narrator Check

Local tools for audiobook and spoken-word production: manuscript length and PFH estimates, ACX chapter repair, podcast loudness normalization and whole-book consistency checks. The tools never upload your files; an opt-in developer API is a separate surface.

Contact: support@narratorcheck.com
Canonical: https://narratorcheck.com/

- [Fix Audio for ACX: Free ACX Audio Checker — Narrator Check](https://narratorcheck.com/) — Free online ACX audio checker: measure RMS, peak, noise floor, format and room tone, fix what is fixable and export a compliant MP3. Nothing is uploaded.
- [Audiobook Calculator: Words to Minutes and Reading Time](https://narratorcheck.com/audiobook-calculator/) — Words to minutes and hours: paste text or open an EPUB, PDF, DOCX or TXT for speaking time, finished audiobook hours, a PFH budget and production time.
- [Room Tone Checker and Fixer for Audiobooks](https://narratorcheck.com/room-tone/) — Measure the room tone at the head and tail of a chapter against ACX and other platforms, then top it up or trim it. Nothing is uploaded.
- [Podcast Loudness Normalizer and LUFS Meter — Narrator Check](https://narratorcheck.com/podcast-loudness-normalizer/) — Measure integrated LUFS and true peak, normalize podcast or voice-over audio to a selected target, and verify the corrected MP3 locally.
- [Audiobook Batch Checker for a Whole Book — Narrator Check](https://narratorcheck.com/audiobook-batch-checker/) — Check a full audiobook batch for ACX failures and chapter-to-chapter RMS, peak and noise-floor consistency, locally in your browser.
- [Test Your Recording Space — Narrator Check](https://narratorcheck.com/test-your-recording-space/) — Measure the noise floor of your room and your voice level with your own microphone, and see if the gap is wide enough for an audiobook that can pass ACX.
- [Mic Test Online: Microphone Test With Real Numbers](https://narratorcheck.com/microphone-test/) — Test your microphone online and see the numbers: level, peak, background noise, sample rate and channels, then play your voice back. Nothing is uploaded.
- [Remove Background Noise From Audio, Free and Local](https://narratorcheck.com/remove-background-noise/) — Clean up a recording in your browser: learn the noise from its own quiet passage, subtract it, and hear the before and after. Nothing is uploaded.
- [Audio Joiner: Merge Audio Into One MP3 or M4B](https://narratorcheck.com/audio-joiner/) — Merge audio files into one MP3, or MP3 to M4B with a chapter per part, in your browser: reorder, reconcile rates and channels. Nothing is uploaded.
- [Trim Audio Online: Cut a Recording, Free](https://narratorcheck.com/trim-audio/) — Cut audio online by typing a start and end in seconds, hear the result beside the original, and download an MP3 at its own rate. Nothing is uploaded.
- [Audio Converter: WAV, AIFF, MP3 and M4A, Local](https://narratorcheck.com/audio-converter/) — A free online audio converter that never uploads your file: WAV, AIFF, MP3 and M4A in, MP3 or uncompressed WAV out, all in your browser.
- [M4A to MP3 Converter, Free and Local](https://narratorcheck.com/m4a-to-mp3/) — Convert M4A or AAC to a 192 kbps MP3 in your browser. The file is never uploaded, there is no account, and you can hear what the encode cost.
- [MP3 to WAV Converter, Free and Local](https://narratorcheck.com/mp3-to-wav/) — Convert an MP3 to an uncompressed 16-bit WAV in your browser, keeping the source sample rate. Nothing is uploaded and no account is needed.
- [WAV to MP3 Converter, Free and Local](https://narratorcheck.com/wav-to-mp3/) — Convert a WAV or AIFF master to a 192 kbps MP3 in your browser, keeping its sample rate, and hear what it cost.
- [Hear Your Manuscript Read Aloud: Free, Private Read-Back](https://narratorcheck.com/hear-your-manuscript/) — Hear an EPUB, DOCX or text manuscript read aloud, chapter by chapter, to proof it by ear. A synthetic voice, run in your browser; nothing is uploaded.
- [Audiobook Pronunciation Guide Builder, Free and Private](https://narratorcheck.com/pronunciation-guide/) — Find the names and unusual words in a manuscript, hear each respelling read aloud, and export the pronunciation guide for your narrator as PDF or text.
- [Proof-Listen an Audiobook Chapter Against the Manuscript](https://narratorcheck.com/proof-listen/) — Compare a recorded chapter with its manuscript word by word: misreads, skipped lines and added words, each with a timecode to hear. Nothing is uploaded.
- [ACX audio requirements, explained one number at a time](https://narratorcheck.com/acx-audio-requirements/) — What the five ACX audio requirements mean, how each is measured, why files fail them and what the fix is, with the official ACX requirements linked.
- [Why ACX rejected your audio file, by the wording it gave you](https://narratorcheck.com/why-was-my-file-rejected/) — One section per rejection reason: what the number means, what causes it, whether it can be fixed in software, and when the honest answer is to re-record.
- [Audacity ACX mastering: the exact chain, and where it breaks](https://narratorcheck.com/audacity-acx-mastering/) — The three-effect Audacity chain for ACX with its exact settings, why each value is what it is, and the open macro bug that blows out audio in Audacity 3.6.
- [Audiobook requirements: ACX, Spotify, Google Play, Apple](https://narratorcheck.com/audiobook-requirements-by-platform/) — What ACX, Spotify, Google Play, Apple and Kobo publish about audiobook audio and AI narration, from their own pages, with the gaps named.
- [How to Record an Audiobook (and Make It Pass ACX)](https://narratorcheck.com/how-to-record-an-audiobook/) — How to make an audiobook at home: room, microphone, levels, room tone, editing, mastering to ACX and checking each file, with a free tool per step.
- [Narrator Check API: ACX check and fix over HTTP](https://narratorcheck.com/developers/) — An HTTP API for ACX chapter checks and fixes, loudness normalization and proof-listening text-to-speech, with presigned uploads and a CLI.
- [Developer account — Narrator Check](https://narratorcheck.com/account/) — Sign in with Google for API keys, usage and your plan. No tool on this site needs an account; this one exists only for the developer API.
- [About Narrator Check — who made this, and why it is free](https://narratorcheck.com/about/) — Why this tool is free, what it does not do, and why nothing you drop on it is uploaded. The honest answers, including the limits.
- [Privacy — Narrator Check](https://narratorcheck.com/privacy/) — How the tools process audio in your tab, which cookieless events are recorded, and what the optional developer API and its accounts keep.
- [Terms — Narrator Check](https://narratorcheck.com/terms/) — The measurable checks Narrator Check performs, their limits, the terms of the optional developer API, and why to keep your original master.
- [Contact — Narrator Check](https://narratorcheck.com/contact/) — Contact Narrator Check support about an audio measurement or refusal without sending your private chapter recording.
- [Licences — Narrator Check](https://narratorcheck.com/licences/) — Every third-party component Narrator Check runs in your browser, its licence, and the GPL source offer for eSpeak NG.

## Key facts

- ACX requires RMS between -23 and -18 dBFS, peak no higher than -3 dBFS, a noise floor of -60 dBFS RMS or lower, 1 to 5 seconds of room tone at each end, and a 192 kbps or higher constant-bitrate MP3 at 44.1 kHz, with each file under 120 minutes. Source: https://help.acx.com/s/article/what-are-the-acx-audio-submission-requirements
- ACX's own Audio Lab checks RMS, peak levels, bitrate, bitrate method, sample rate, mixed channels, duplicate files and spacing - and does NOT check noise floor, which human Quality Control rejects for. Source: https://help.acx.com/s/article/acx-audio-analysis-tool-faq-s
- Passing any automated analysis, including this site's, does not guarantee ACX approval: human QA judges pronunciation, extraneous sounds and consistency that no meter measures.
- ACX states RMS can be measured in multiple ways, which is why DAW meters disagree with each other and with ACX.
- Narrator Check measures all of these in the browser, corrects the correctable ones, re-encodes a 192 kbps CBR MP3 and re-measures its own output before offering it. The tools never upload audio; every check and fix runs in the browser tab. A separate, opt-in developer API (https://narratorcheck.com/developers/) processes only the files its key holders send to it.
- Apple's podcast requirements ask for about -16 dB LKFS within 1 dB and true peak no higher than -1 dBFS. Google Play Books asks for MP3 at 128 kbps or higher mono, 256 kbps or higher stereo, CBR preferred. Apple Books publishes an audiobook specification but no loudness or peak levels; it asks for 22.05 kHz 16-bit as a minimum, and inverts everyone else's file structure — a book under 23 hours must be delivered as a single track, and only above that may it be split into at most 25 tracks of at least 60 minutes each.