Guides · Reference
Audiobook production glossary
The words you meet making an audiobook, in plain language, with a note on what StellAurator does about each one. ACX’s figures are as ACX published them in October 2026.
A
- Acoustic treatment
- Soft, absorbent material that reduces echo in the recording space, so the voice sounds close and dry. See the room treatment guide.
- ACX (Audiobook Creation Exchange)
- Audible’s service for producing audiobooks and submitting them for sale on Audible and Amazon, and on Apple Books. Every file is reviewed against ACX’s Audio Submission Requirements before the book goes on sale. StellAurator exports one file per chapter in the format ACX requires and measures each chapter against those requirements first. See ACX’s audio requirements, explained.
- ACX Audio Submission Requirements
- The technical rules every ACX file must meet. The levels: loudness between -23 dB and -18 dB RMS, peaks below -3 dB, a noise floor below -60 dB RMS. The files: MP3 at a constant 192 kbps or higher at 44.1 kHz, room tone at the start and end, at most 120 minutes per file, one chapter or section per file. The ACX check in StellAurator measures the loudness, the peaks, the noise floor and the file format, before and after processing, and reports a pass or a fail. ACX also reviews the performance and the rights.
- ACX check
- A measurement of a file against ACX’s technical requirements. Several programs offer one. It measures the numbers; the performance and the rights are ACX’s review. StellAurator runs it in Finish, for a chapter or the whole book.
- Audible
- Amazon’s audiobook store and subscription service. Independent authors reach it through ACX.
- Audio interface
- A box that connects a studio microphone, by its XLR cable, to a computer and powers it. StellAurator works with any microphone Windows sees. See the audio interface guide.
- Audiobook production
- Everything between a finished manuscript and finished audio files: casting or choosing the narrator, recording, editing, cleaning up, mastering to a store’s requirements, proof listening, and export. StellAurator does every one of these steps in one Windows program.
- Audiobook recording software
- A program used to record narration. General audio editors record a waveform; audiobook-specific software records against the text of the book. StellAurator records from the manuscript, and every recording is stored on the line it belongs to.
B
- Bit depth
- How finely each sample measures the level. Recordings are commonly made at 24 bit or 16 bit.
- Bit rate (CBR and VBR)
- How much data each second of a compressed file uses. CBR (constant bit rate) keeps it the same throughout; VBR (variable bit rate) changes it. ACX requires constant bit rate MP3 at 192 kbps or higher.
- Breaths
- The sound of the narrator breathing between phrases. Productions lower breaths and leave them in; a reading with no breaths sounds wrong. StellAurator lowers breaths and does not remove them, and you mark a breath you want left alone.
C
- Chapter file
- One file per chapter or section of the book, which is how ACX expects a book to be delivered.
- Clipping
- Distortion that happens when a signal goes past the loudest level the recording can hold. A clipped peak does not repair cleanly, so it is avoided while recording.
- Closed-back headphones
- Headphones that keep their sound from leaking into the microphone while you record. See the headphone guide.
- Compression
- A process that narrows the difference between the louder and quieter passages of a recording, so the narration sits at a more even level.
D
- DAW (digital audio workstation)
- A general program for recording and editing audio on a timeline. Many narrators use one for audiobooks. StellAurator is built around the manuscript instead. Its timeline shows the chapter’s lines with their recordings, and the music and sound effects under them.
- Decibel (dB, dBFS)
- The unit used to measure audio level. In digital audio, levels are measured below full scale (dBFS), where 0 dB is the loudest level a file can hold, so useful levels are negative numbers.
- Dual narration
- An audiobook read by two narrators, one for each point-of-view character, who take turns chapter by chapter.
- Duet narration
- An audiobook in which two narrators share scenes, each reading their own characters’ lines, so the voices alternate within a chapter.
- Dynamic and condenser microphones
- The two common kinds of studio microphone. A dynamic microphone picks up less of the room; a condenser picks up more detail and more of the room.
E
- Equalization (EQ)
- Adjusting the balance between the low and the high frequencies in a recording. StellAurator’s tone controls adjust the warmth and the air of a voice, and its presence.
F
- False start
- A reading abandoned partway, followed at once by a second attempt at the same words. After a false start, you choose in StellAurator which reading to keep.
- Full cast (multicast) audiobook
- An audiobook in which each character is read by a different voice, instead of one narrator reading everything. StellAurator casts each character separately and sends each actor the lines assigned to them alone.
H
- Hum
- A steady low tone from electrical interference, at 50 or 60 Hz, the frequency of the mains. StellAurator analyzes recordings for hum and suggests a fix.
L
- Limiter
- A processor that stops peaks from going past a set ceiling, such as -3 dB for ACX, after the overall level has been raised.
- Line
- One unit of the manuscript as it is recorded: a sentence or a short passage of narration or dialogue. In StellAurator every recording is placed on its line, with its waveform and length, and the line is marked as recorded.
- LUFS
- Loudness units relative to full scale, a measure of perceived loudness used by streaming services. ACX states its loudness requirement in RMS instead.
M
- M4B
- An audiobook file format that can hold the whole book in one file, with chapter markers. StellAurator exports one M4B with a chapter mark at the start of each chapter and the book’s title and author, for stores other than ACX.
- Manuscript
- The text of the book being recorded. StellAurator opens a Word file, a PDF or an EPUB as a manuscript, or pasted text.
- Mastering
- The last processing step before delivery: setting the final level, controlling peaks and checking every file against the store’s requirements. In StellAurator, Finish takes a chapter or the whole book through Diagnose, Plan, Apply, Check and Export.
- Mono and stereo
- Mono is one channel of audio; stereo is two. A single narrator is recorded in mono. ACX accepts either, and every file in the book has to match.
- Mouth clicks
- Small clicks and pops from the mouth and tongue that a microphone picks up. StellAurator marks the clicks and pops in a recording and repairs them, and Undo takes any fix back.
- MP3
- A compressed audio file format. ACX requires MP3 files for submission.
- Music bed
- Music played quietly under narration for a stretch of the book. Beds and music cues go on the chapter’s timeline in StellAurator’s Score mode.
N
- Narrator
- The person who reads the book aloud. In a full-cast production, the narrator reads the narration and actors read the characters. See StellAurator for narrators.
- Noise floor
- The level of a recording when nobody is speaking: the room, fans, the street and the microphone’s own hiss. ACX requires it below -60 dB RMS. StellAurator shows a live background noise meter while you record and measures the noise floor in its ACX check.
- Noise reduction
- Processing that lowers steady background noise. Heavy noise reduction leaves a voice thin or watery, which reviewers hear. StellAurator reduces background noise only where it is audible.
- Normalization
- Raising or lowering a whole recording to a target level. StellAurator sets each chapter’s loudness on export (for ACX, -20 dB RMS with peaks held at -3 dB). Its Normalize tool takes a target in LUFS or RMS, or a peak or true-peak ceiling.
O
- Opening credits and closing credits
- Short spoken passages that name the title, the author and the narrator at the start and end of the audiobook. ACX expects them in their own files.
P
- Peak
- The single loudest sample in a file. ACX requires peaks below -3 dB.
- Per finished hour (PFH)
- How narration and production fees are quoted: a rate for each hour of the finished audiobook, not each hour of work.
- Pickup (pickups)
- A line or passage recorded again after the main recording, to fix a mistake, a misreading or a noise found in proof listening. Lines you mark in StellAurator collect in the Pickups list, where you record each one again or send it back to the actor who recorded it.
- Plosive
- A burst of air from P and B sounds that hits the microphone as a thump. A pop filter and microphone placement reduce them. StellAurator analyzes recordings for plosives and suggests a fix.
- Pop filter
- A screen in front of the microphone that softens plosives.
- Producer
- The person or company that records and finishes an audiobook. On ACX a narrator who also edits and masters is the producer too.
- Proof listening (proofing)
- Listening to the finished audio while following the text, to catch a misread or skipped word, a noise or an audible edit. Proof listen in StellAurator plays a chapter as it will be exported and ticks off each line as it is heard. Press F to mark a line for recording again without stopping playback.
- Punch and roll (punch-and-roll recording)
- A recording method in which the narrator stops at a mistake, plays back the moments just before it, and records again from that point. The mistake is replaced as the narration goes.
R
- Retail sample
- The short excerpt a store plays to shoppers. ACX’s runs one to five minutes, taken from the audiobook, with no explicit material.
- Rights holder
- The person or company that owns the audio rights to the book: the author, or the publisher when the author has sold them.
- RMS (root mean square)
- The average level of a whole file, not its loudest moment. ACX requires every file to measure between -23 dB and -18 dB RMS.
- Room tone
- The sound of the recording space with nobody speaking. ACX asks for room tone at the start and end of each file, and editors use it to fill gaps so the background stays even.
- An ACX arrangement in which the rights holder and the narrator or producer split the audiobook’s royalties instead of paying a fee per finished hour.
- Rumble
- Low-frequency noise from traffic, footsteps, air conditioning or a desk being bumped. StellAurator’s tidy-up settings include a rumble cut, applied to the book’s recordings once it is set.
S
- Sample rate
- How many times per second the sound is measured. ACX requires 44.1 kHz (44,100 times a second) for the files it receives.
- Sibilance (and de-essing)
- Harsh or hissing S sounds. A de-esser softens them. StellAurator’s tidy-up settings include an S softener, and its repair tools include a de-esser.
- Spool
- StellAurator’s word for one complete reading of the book. A book holds several spools, and the export takes a whole spool or the recordings you select.
T
- Take
- One recorded attempt at a line or passage. A narrator records several takes and keeps the best. Every take stays on its line in StellAurator, and you choose an earlier reading again whenever you like.
- Teleprompter
- A display of the script that scrolls while the narrator reads, so the narrator does not look away or touch the recording controls. StellAurator’s teleprompter holds the current line in a highlighted band and scrolls at the pace you set. You stop and reread a sentence, then continue.
- Text to speech (TTS)
- Speech generated by a computer from written text, also called a synthetic or AI voice. StellAurator includes twenty-six built-in computer voices that work offline, and connects to outside voice services if you want them. ACX does not accept computer-generated narration.
- Timeline
- The view of a project laid out in time, with a track for the voice and tracks for music and sound effects.
U
- USB microphone
- A microphone that plugs straight into a computer, with no interface needed. See the microphone guide.
V
- Voice conversion (speech-to-speech)
- Technology that changes a recorded voice into another voice while keeping the original timing and delivery. In StellAurator, with a voice conversion service connected, your own reading becomes each character’s voice. The converted take is stored beside your original, and the file is marked as a speech-to-speech modified human performance.
W
- WAV
- An uncompressed audio file format, used for recording and editing.
Record your audiobook in StellAurator
Every step in this glossary, from the teleprompter to the ACX check, is in the free 7-day trial. Exporting the finished audiobook is not. No card.