Editing and mastering are both required for a professional audiobook, but they do completely different things. Editing is about content: removing mistakes, cleaning up noise, and making the narration sound polished. Mastering is about numbers: adjusting loudness, peaks, and noise floor to meet the technical specifications platforms like ACX require. You finish editing first, then master. Do either one wrong, or skip one entirely, and your audiobook will fail submission.
What Is Audiobook Editing?
Editing transforms a raw recording into a clean, finished performance. It is a content operation, not a technical one. The editor's job is to ensure the audio sounds natural and mistake-free, not to hit any particular loudness target.
What Does Editing Actually Involve?
Removing mistakes and retakes. False starts, stumbles, re-reads, and any passages recorded twice need to be cut and replaced with clean room tone so the pacing flows naturally.[1]
Cleaning mouth noise. Tongue clicks, lip smacks, and saliva sounds are picked up by sensitive condenser microphones and are distracting over a long listen. Editors remove these individually using spectral editing tools or automated de-click processing. ACX instructs producers to "remove extraneous sounds from your recording (mouth noises, pops, keyboard clicks, etc.)" before submitting.[1]
Managing breaths. Not all breaths are removed. Loud, gaspy breaths at the start of a paragraph typically get cut or reduced. Breaths within sentences are often left in place because removing them all makes the narration sound robotic. The standard practice is to lower the level of distracting breaths or replace them with silence, rather than deleting every breath in the file.[2]
Adjusting pacing. Accidental long pauses (losing your place, hesitating on a word) get trimmed. Dramatic pauses written into the text get left in or even lengthened. The goal is a narration that feels intentional throughout, with no dead air that sounds like an error.[2]
Ensuring room tone consistency. When you cut out a mistake, you leave a gap. That gap must be filled with room tone, the ambient silence of your recording environment, rather than digital silence (absolute zero). Digital silence creates an audible and unnatural transition. Room tone recorded at the start of each session provides the material for these repairs.[1]
Verifying manuscript accuracy. An editor listens to the narration while following the manuscript to catch mispronounced names, skipped sentences, and wrong words. ACX's human reviewers do the same check. Errors they find cause rejection.[3]
Re-recording pickups. Sections that can't be fixed in editing, because the noise is too embedded in the narration or the performance needs to be re-done, go back to the narrator as "pickups." These re-recorded sections are then cut into the original audio and must match the recording characteristics of the surrounding material.
What Editing Does Not Do
Editing does not adjust loudness. It does not set your peak level. It does not change your noise floor measurement. It does not convert your file format or add silence padding. All of those are mastering tasks.
This distinction matters practically: if you start mastering before editing is complete, any subsequent edit (removing a click, cutting a sentence, inserting a pickup) changes the audio content, which changes the loudness and noise floor. You would need to master again. The rule is simple: complete all editing before mastering begins. For a full breakdown of the production sequence, see the audiobook production workflow guide.
What Is Audiobook Mastering?
Mastering is the final technical processing stage. It takes your clean, edited recording and adjusts it to meet the measurable specifications that distribution platforms require. For audiobooks, those specifications are fixed numbers, not creative targets.
What Does Mastering Actually Involve?
Loudness normalisation to meet RMS requirements. ACX requires an RMS loudness between -23 and -18 dBFS.[4] Raw home recordings typically land between -28 and -35 dBFS, well below the floor. Mastering brings the average loudness into range consistently across every chapter file.
Peak limiting below -3 dBFS. No true peak in your audio can exceed -3 dBFS. A true-peak limiter, not a standard sample-peak limiter, catches inter-sample peaks that occur between digital samples and cause distortion on playback devices.[4] For the full explanation see audiobook true peak explained.
Noise floor management below -60 dBFS. The silence between sentences must measure below -60 dBFS. This threshold is quieter than most home offices. When loudness normalisation raises your overall level, it raises the noise floor too. Mastering manages this through high-pass filtering and, where needed, targeted noise reduction before the gain stage.[4] The audiobook noise floor guide covers this in detail.
Format conversion. ACX requires mono MP3 at 44,100 Hz and 192 kbps CBR. This is a binary specification: any other format causes instant automated rejection. Format conversion is always the final step because MP3 encoding can shift peak levels by 0.5 to 1 dB, so you verify the encoded output, not the WAV before encoding.[4]
Silence padding. Each chapter needs 0.5 to 1 second of room tone at the head and 1 to 5 seconds at the tail. This is a separate specification from noise floor. The silence must be room tone, not digital silence. For the details, see audiobook silence padding explained.
What Mastering Does Not Do
Mastering does not remove clicks or mouth noise. It does not fix echo or reverb baked into a recording. It does not correct mispronunciations. It does not adjust pacing. It does not add opening or closing credits. Those are all editing and performance concerns.
This is one of the most common misunderstandings in audiobook production: narrators assume mastering will "clean up" their recording. It will not. Mastering operates on numbers (levels, peaks, format). A click that was in the recording before mastering will still be in the recording after mastering, just at a different overall level. See what ChapterPass does and does not do for a precise breakdown.
When Does Each Stage Happen in the Production Workflow?
The four-stage audiobook production pipeline is: recording, editing, mastering, submission. Editing and mastering are never interchangeable, and they never happen in parallel.
1. Recording. You capture narration in a treated space. Record at 24-bit, 44.1 kHz or higher. Record 30 to 60 seconds of room tone at the start of every session; you will use this for gap-fills and silence padding.
2. Editing. You clean the raw recording. Remove mistakes, manage breaths, cut mouth noise, verify manuscript accuracy, insert pickups. Deliver a finished performance that sounds natural and polished. Do not touch loudness or peaks at this stage.
3. Mastering. You process the clean, edited file through the technical signal chain: high-pass filter, compression, loudness normalisation, peak limiting, noise floor verification, silence padding, format conversion. Every chapter gets identical settings to ensure consistency across the book.
4. Submission. You upload verified, compliant files to ACX or your distributor. The ACX submission page and the ACX audio requirements guide cover the full spec table.
The one-way dependency is: editing must be finished before mastering begins. There is no equivalent constraint between recording and editing; you can edit as you record if you prefer.
Can You Skip Editing?
No. Skipping editing and going straight to mastering is the most common mistake first-time narrators make. Mastering cannot compensate for what editing missed.
Clicks and pops in your audio will still be clicks and pops after mastering. They will be at a slightly different level, but they will be audible, and ACX's human reviewers will flag them. Echo and room reverb are embedded in the recording; no level adjustment removes them. Manuscript errors, mispronounced words, and skipped sentences remain exactly as you recorded them.
The ACX human quality review exists specifically to catch what automated checks cannot: editing failures. An audiobook with perfect mastering numbers but audible mouth clicks, inconsistent room tone, or misread passages will still be rejected. ACX's guide to reviewing audio states that reviewers listen for "extraneous background noises," "double takes the producer may have forgotten to take out," and "mispronunciations of names, places, or terms."[3] None of those are mastering problems.
Can You Skip Mastering?
No. A cleanly edited recording that has not been mastered will fail ACX's automated technical checks.
Raw recordings almost always have the wrong loudness (-28 to -35 dBFS typical versus the required -23 to -18 dBFS), peaks that exceed -3 dBFS, noise floors that drift above -60 dBFS when loudness is adjusted, and the wrong file format. Every one of these is a binary fail in ACX's automated check layer. The check runs before a human reviewer ever hears your audio.
Beyond format compliance, consistency across chapters is a mastering responsibility. If you apply different processing settings to different chapters, or no processing at all, the loudness will vary noticeably from chapter to chapter. ACX reviewers flag inconsistency during the human review pass.[4] Batch-processing all chapters through identical mastering settings is the standard solution.
What Does ACX Check That Relates to Each?
ACX runs two independent review layers on every submitted audiobook.[4]
The Automated Technical Check (Mastering)
This is a system measurement against eight specifications. It runs first, before any human listens to your audio. Files that fail any one spec are rejected automatically. The eight specs are:
- RMS loudness: -23 to -18 dBFS
- True peak: below -3 dBFS
- Noise floor: below -60 dBFS
- Sample rate: 44,100 Hz
- Channels: mono
- Format: MP3, 192 kbps CBR
- Head silence: 0.5 to 1 second
- Tail silence: 1 to 5 seconds
These are all mastering outputs. A correctly mastered file passes every one of them. For the complete technical detail on each spec, see the ACX audio requirements guide.
The Human Quality Review (Editing)
After the automated check passes, a human reviewer listens to your audio. This is where editing quality gets evaluated. The reviewer listens for clicks, pops, and mouth noise; room echo and reverb; double-takes and unedited retakes; inconsistent recording characteristics between chapters; mispronounced words and manuscript deviations; and whether the narration is human (ACX does not accept AI-generated audio outside its Voice Replica programme).[3]
These are all editing-stage concerns. No mastering tool catches them. A technically perfect file with audible mouth clicks will be rejected at the human review stage. The full breakdown of what ACX checks covers both layers in detail.
How Does ChapterPass Fit In?
ChapterPass is a mastering tool. It handles the automated technical check layer: loudness, peaks, noise floor, format, and silence padding. It takes your edited chapter files and processes them to meet all eight ACX specifications, then verifies every output before you download.[4]
ChapterPass does not edit your audio. It does not remove mouth noise, clean clicks, fix echo, or adjust pacing. Those steps need to happen in your editing software, before you upload to ChapterPass.
The workflow is: edit your chapters in your DAW until the performance is clean and correct, then upload to ChapterPass for mastering. First file is free, so you can verify the output on your first chapter before committing the rest.
ChapterPass is also a complement to the editing work you have already done, not a shortcut around it. A clean edit produces better mastering output because there is less unwanted noise to manage. A mastered file that still has clicks and pops will fail at the human review stage regardless of how accurate the technical numbers are.
For narrators earlier in the process, the guide to preparing your audiobook for ACX covers the complete workflow from recording setup to final submission.
Editing vs Mastering: Side by Side
| Editing | Mastering | |
|---|---|---|
| Goal | Clean, accurate performance | Technical spec compliance |
| Input | Raw recording | Finished, edited file |
| Output | Polished narration | Submission-ready file |
| What it fixes | Mistakes, noise, pacing, manuscript errors | Loudness, peaks, noise floor, format |
| What it cannot fix | Wrong loudness, bad format | Clicks, echo, mispronunciations |
| When it happens | Second stage | Third stage |
| ACX check it affects | Human quality review | Automated technical check |
| Can be automated | Partially (de-click, breath removal) | Yes, for fixed specs |
| Required for submission | Yes | Yes |
Frequently Asked Questions
Do I need to edit before I master?
Yes, always. Mastering processes the entire file; any edit you make after mastering (removing a click, inserting a pickup) changes the audio content, which changes the loudness. If you edit after mastering, you need to master again. Finish all editing first, then master the finished file.
Can mastering fix a noisy recording?
Not if the noise is under your narration. Mastering can manage the noise floor during silent sections (between sentences) to keep it below -60 dBFS. It cannot remove noise that is present at the same time as your narration, because any processing aggressive enough to remove the noise would damage the voice signal too. The fix is to re-record in a quieter environment.
What is the difference between editing and mixing for audiobooks?
Editing removes problems from a single recording. Mixing balances multiple audio elements into one output, for example, two narrators recorded separately, or narration combined with background music. Most single-narrator audiobooks require editing and mastering but not mixing. For the full comparison, see audiobook mastering vs mixing.
Does ChapterPass do any editing?
No. ChapterPass handles technical mastering only: loudness normalisation, peak limiting, noise floor management, format conversion, and silence padding. It does not remove clicks, manage breaths, fix pacing, or correct any content in your recording. Edit your chapters first, then upload to ChapterPass for mastering.