Producing an audiobook that meets ACX’s rigorous technical standards is the gateway to distribution on Audible, iTunes, and Amazon. Every year, thousands of submissions are rejected for simple, avoidable issues—background noise, clipped peaks, or mismatched loudness. Understanding how to properly record and edit audiobooks not only saves you hours of rework but also ensures your narration sounds polished and professional to listeners. This expanded guide walks you through every stage of the process, from room treatment and microphone technique to editing, mastering, and final quality control, so you can confidently submit an ACX-compliant master.

Preparing Your Recording Environment

Your recording space is the foundation of a clean audiobook. Even the best microphone cannot fix a room full of echo, street noise, or HVAC hum. The ACX requirement for background noise is no more than –60 dB relative to the signal—that is extremely quiet. Achieving this starts with treating your environment.

Choosing a Quiet Space

Select a room with minimal hard surfaces. If you do not have a dedicated vocal booth, a walk-in closet filled with clothes works well. Avoid rooms with bare walls, tile floors, or large windows. Use heavy curtains, blankets, or acoustic foam to absorb sound. The goal is to eliminate slap echo (quick reflections) and external noise. If you record on a budget, build a portable vocal booth using PVC pipe and moving blankets—a common solution used by professional voice actors.

Microphone and Equipment Setup

Use a large-diaphragm condenser microphone or a high-quality dynamic microphone. For most narrators, a cardioid condenser (e.g., Rode NT1-A, Audio-Technica AT2020) works well. Pair it with an audio interface (Focusrite Scarlett 2i2 or similar) that provides clean preamps and phantom power. Set the gain so your voice peaks around –6 dB to –3 dB—never hitting 0 dB (digital clipping). Use a suspension boom arm and a shock mount to reduce vibrations from footfalls or desk movements.

A pop filter is essential. Place it 2–3 inches from the microphone grille. This stops plosive sounds (p, b, t) from causing low-frequency thumps. Test your position by saying “Peter Piper picked a peck of pickled peppers.” If the filter works, you should hear no puff of air. Keep your microphone at a consistent distance: 6–12 inches is typical. Closer gives a warmer, more intimate sound; further away reduces proximity effect but may capture more room tone. Pick one distance and stick to it throughout the recording.

Recording Techniques for Professional Audiobooks

With your environment set, the next step is capturing a clean, consistent performance. ACX requires that each audio file be free of audible clicks, pops, mouth noises, and excessive breaths. Good recording technique reduces cleanup later.

Maintaining Consistency

Position your microphone at the same angle and distance for every session. Mark the spot on the floor with tape. If you move your head while reading, the volume fluctuates—forcing you to apply heavy compression later. Speak clearly, at a steady pace, with natural intonation. Do not whisper or shout; aim for a dynamic range that stays within the –24 dB to –3 dB window.

Managing Breaths and Mouth Noises

Hydrate well before and during recording. Dry mouth creates clicks and smacks. Avoid dairy or sugary drinks—they cause excess saliva. Take small sips of room-temperature water. For breaths, you have two options: record natural breaths (most listeners expect them) or edit them out if they are too loud. In editing, you can reduce breath levels instead of removing them entirely, preserving a natural flow. For now, just try to keep breathing quiet and consistent.

Recording in Segments

Do not record an entire chapter in one take. Break it into paragraphs or logical sections (every 3–5 minutes). After a mistake, pause for a few seconds, then repeat the line from the beginning of that sentence or phrase. This makes editing simpler—you will see the silence as a visual gap in your waveform and can easily delete the error. Many producers also use a “punch-and-roll” technique: when you flub a line, roll back a few seconds and record over it. In Audacity, you can use the “Punch and Roll” tool; in Reaper, it is built into the recording settings.

Editing Your Audiobook to ACX Standards

Once the raw recording is done, editing separates a hobbyist from a professional. ACX does not specify exact editing steps, but their submission requirements (noise floor, peak level, loudness) demand careful cleanup. Plan on spending two to three hours of editing for every finished hour of audio.

Removing Mistakes and Long Pauses

Start by trimming the silence at the beginning and end of each file to no more than 1 second. Then go through the waveform visually: highlight and delete section where you flubbed words, made lip smacks, or there are coughs. For long pauses (more than one second), shorten them. Normal pauses for punctuation should be between 0.2 and 0.5 seconds. Chapter breaks typically have 1–2 seconds of silence.

Noise Reduction

Apply noise reduction after you have removed all audible errors. Use the “Noise Print” method: select a segment of pure room tone (silence during a pause) of about 2–3 seconds. In Audacity, go to Effect → Noise Reduction → Get Noise Profile. Then select the entire track, apply with settings: Noise Reduction (dB) 12–18, Sensitivity 6.00, Frequency Smoothing 3 bands. Too aggressive reduction causes “whispering” artifacts; always preview. For professional results, use a noise gate to eliminate low-level hum between phrases, set to –50 dB threshold, with a fast attack and slow release.

Mouth Click Removal

Isolated clicks can be removed manually. Zoom into the waveform: clicks appear as sharp spikes. In Audacity, use the “Repair” tool (Effect → Repair) or just delete a few milliseconds around the click and crossfade the gap. Alternatively, use spectral editing (in Adobe Audition or Izotope RX) to see the sound and remove it without affecting surrounding audio.

Volume Leveling and Compression

ACX requires the integrated loudness to be –18 LUFS (plus/minus 2 dB), with a maximum peak of –3 dB. To achieve this, first normalize all files to a consistent RMS level (e.g., –18 dB RMS). Then apply light compression: a compressor with a ratio of 3:1, threshold around –20 dB, attack 10 ms, release 100 ms. This smooths out loud and quiet passages without sounding squashed. After compression, use a limiter set to –3 dB to catch any errant peaks. Finally, check the integrated loudness with a loudness meter (e.g., Youlean Loudness Meter). Adjust the overall gain so the track sits at –18 LUFS.

Mastering to Meet ACX Technical Specifications

Mastering is the final processing that ensures every file conforms to ACX’s exacting requirements. The official ACX Audio Submission Requirements list these key specifications:

  • Sample Rate: 44.1 kHz (this is the standard for audio CDs; do not use 48 kHz).
  • Bit Depth: 16-bit (24-bit is acceptable for production but ACX requires a 16-bit final file).
  • Channels: Mono or Stereo. Mono is preferred because audiobooks are listened to on a single speaker or earbud, and mono reduces file size. If you record in stereo (same audio on both channels) you must sum to mono or leave it as dual mono. ACX accepts both, but mono is simpler.
  • Peak Level: No higher than –3 dBFS. This headroom prevents distortion on playback devices. Use a hard limiter to ensure peaks never exceed –3 dB.
  • Background Noise: No more than –60 dB relative to the speech level. This is measured in the quietest part of the file (between words). If your noise floor is above –60 dB, you will need stronger noise reduction or a quieter recording environment.

Additionally, ACX specifies a loudness range (LRA) of 8–12 for most content, but the primary metric is Integrated Loudness (–18 LUFS). To verify all specs, use the ACX Check tool in Pro Tools, or a third-party plugin like MeterPlugs Loudness Analyzer. Export each chapter as a WAV file (PCM format, no compression) with the naming convention: TitleNumber_AuthorName_PartNumber (e.g., HowToWrite_JDoe_Ch01.wav).

Setting Up Your DAW for ACX Compliance

In any editing software, set your project sample rate to 44.1 kHz. When exporting, choose “WAV (Microsoft) signed 16-bit PCM”. Do not use MP3 or any compressed format. For stereo files, ensure both channels are identical; if not, you can convert to mono. A quick way in Audacity: Tracks → Mix → Mix Stereo Down to Mono. In Reaper, set the track to mono and record that way.

Quality Control and Final Submission

Before you upload to ACX, listen through the entire audiobook on good headphones (closed-back to simulate a listener’s experience). Pay attention to:

  • Consistency – Does the volume vary between chapters? Use loudness normalization across all files to match.
  • Errors – Are there any remaining misreads, background bumps, or digital glitches? Mark them with markers and fix.
  • Headroom – Use a peak meter to confirm no file exceeds –3 dBFS.
  • Noise floor – In a quiet section, use a spectral analyzer or check the RMS level. If you see noise above –60 dB, apply additional noise reduction or retake that section.

You can also run your files through free ACX checkers like the Audacity “ACX Check” plugin (available in the Audacity manual) or the web-based Audiobook Adventures ACX Check. Many producers use Adobe Audition with the “Match Loudness” panel to batch-normalize all files to –18 LUFS. Reaper also has built-in loudness analysis with the SWS extension.

While you can produce ACX-compliant audiobooks with free software like Audacity, professional tools speed up the workflow. Here are the most commonly used:

  • Audacity – Free, open-source, and widely used. The ACX Check plugin is a must.
  • Adobe Audition – Excellent spectral editing, noise reduction, and batch loudness matching.
  • Reaper – Affordable, highly customizable, and lightweight. Ideal for long-form projects.
  • iZotope RX – Industry-standard spectral repair for removing clicks, mouth noises, and hum. Used by professional post-production houses.

For detailed guidelines, always refer to the official ACX Audio Submission Requirements page. It contains the most up-to-date specifications, including acceptable file formats, naming conventions, and metadata.

Meeting ACX’s mastering standards is achievable with careful planning and methodical editing. By treating your recording environment, capturing a consistent performance, editing meticulously, and mastering within the required loudness and peak limits, you will submit audiobooks that pass quality control on the first try. The effort you invest in proper technique pays off in positive reviews, more sales, and a reputation as a reliable producer in the growing audiobook market.