An Audiobook Audio Preflight Before You Submit to ACX
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An audiobook preflight should answer two different questions: does the exported file meet the submission specifications, and does the finished recording sound right from beginning to end? Treating those as separate checks makes it easier to find a technical failure without overlooking a repeated line, awkward edit or change in narration tone.
Use the workflow below to organize your files, measurements and listening notes before submission. It is a quality-control plan, not a guarantee of ACX acceptance, and the current official requirements remain the reference for your project.
Keep a dated requirements reference
Requirements checked: 8 October 2026. ACX's official submission guidance, dated 15 April 2026, specifies:
- Average file level: −23 to −18 dB RMS
- Peaks: no higher than −3 dB
- Noise floor: no higher than −60 dB RMS
- Export: MP3 at 44.1 kHz, using constant bit rate of at least 192 kbps
- Channels: consistent across the book, either all mono or all stereo
- Room tone: 1–5 seconds recommended at each end, with spacing not exceeding 5 seconds
- Organization: one chapter or section per file, with separate opening and closing credits
Check the complete ACX audio submission requirements for content, credits, file naming and any updates before uploading. These file-level specifications do not describe a booth's sound-reduction performance.
Build a file inventory before measuring
Create a list of every intended delivery file. Give each an identifiable version and mark which session or master produced it. Keep working files apart from the folder you intend to upload so an old export cannot be mistaken for the final version.
Record the file's place in the book, the script or manuscript version used, and any unresolved pickup. This inventory is your control sheet. If the narrator, editor and mastering engineer are different people, agree on who updates it and who closes an open issue.
A file should move into the delivery folder only after its current export has been checked. A successful check on an earlier revision does not validate a later file with the same name.
Measure the exported file, not only the session
Use tools appropriate for the specified measurements and record which file you tested. Note the tool and version alongside the result. Do not substitute a differently labeled loudness measurement for RMS or assume two meters are reporting the same quantity.
If a result is unclear, ask an audiobook engineer to interpret the reading and the measurement method. The goal is to understand and correct the file, rather than repeatedly changing settings until one display looks acceptable.
After any change to the master or export settings, create a new labeled export and check that version again. Keep a short revision note explaining what was changed. That makes it possible to trace a failed check back to its source without guessing which copy was tested.
Use automated analysis within its limits
ACX's audio-quality guidance describes Audio Lab checks for properties including RMS, peaks, encoding, channels and spacing. It also states that Audio Lab does not detect noise-floor problems or editing errors.
Use its results as one part of the preflight. Save the report with the matching file version, review any flagged issue and retain separate tasks for the checks that the tool does not perform. An automated pass cannot tell you that the manuscript was read correctly or that an edit is musically and conversationally natural.
Only upload material to an analysis service when you have the necessary rights and project permission. Confidential narration should follow the client's approved handling process.
Listen through the actual delivery file
Set aside a listening pass in which you follow the current manuscript and note problems without stopping to repair each one immediately. Use timestamps and concise descriptions so the editor can locate the issue later.
Check the beginning and ending, the transitions between paragraphs, proper names and any section that required a pickup. Listen for missing or repeated words, changes in background sound, distracting mouth or handling noises and edits that cut into a word or breath unnaturally.
Then compare neighboring chapter openings and endings. The whole book is a listening experience, not merely a folder of individually checked files. A noticeable change deserves investigation even when each file's measurements look acceptable.
Keep playback comfortable. Raising a quiet interval to an extreme listening level may reveal detail, but do not confuse that diagnostic exercise with the listener's ordinary experience or a properly performed measurement.
Try a small original preflight exercise
Before committing the full book to a workflow, rehearse the process with a short original passage such as:
“The studio window caught the last light of the evening. Nora set her notes beside the microphone, checked the first line, and began again with a quieter voice.”
This passage is provided for your own practice; no recording or measured result is supplied here. Record it with your intended setup, preserve the source file and create an export using the planned delivery settings.
Give the export a version name, measure it, save the results and listen while reading the text. If you make a revision, repeat the check on the new export. The useful outcome is a working process and an honest record of what you found, not a fictional “passing” example.
Keep recording-space decisions separate
If the preflight reveals recurring background interruptions or a tonal problem, return to the recording setup before assuming that another export setting will solve it. Identify whether the concern involves the performance, equipment, sound within the room or sound entering from elsewhere.
Review interior acoustic treatment for the sound within a booth and ventilation options for the intended recording workflow. Follow required operating instructions during tests. A file's noise-floor result is not a booth isolation rating, and a booth cannot guarantee that an audiobook will meet every delivery requirement.
Close the preflight with a clear record
For each final file, retain its version, export settings, measurement report, listening-check date and unresolved issues. Record who confirmed a correction when several people are involved. Check that the file selected for upload is the same one that completed the process.
Finish by opening the current official requirements again. A careful preflight gives you evidence that the files were reviewed and a straightforward way to address questions. ACX's final acceptance process remains separate from your internal checklist.