Tag Archives: audio submission requirements

A Critical Ear: The ACX Reference Sample Pack

Hi! This is Brendan from the ACX QA Team. I’m here today to introduce our Reference Sample Pack, a new tool we’ve developed to illustrate how your audiobook should—and should not—sound during the various stages of production.

This tool will help you spot problems in your audio and give you an idea of the audio quality your listeners will be expecting from productions on Audible. We’ve also included files that can be used to calibrate your Digital Audio Workstation (DAW) for recording. Mastering level specifications, especially RMS, can be difficult to understand via text alone. What better way to learn what kind of audio “passes” ACX QA than to have passable files at hand for you to refer to and test on your own setup?

Getting Started

To use the Reference Sample Pack, download the zip file onto your computer. Unzip this folder and you will find nine WAV files that can be loaded into your DAW of choice. We processed, and in some cases distorted, the same raw file for each example, then divided the samples into two categories: files that can be used as good production targets, and files containing issues you should try to avoid.

What’s Inside

Start with our PDF guide, which contains exact details on what you should listen for while playing.


The “Good Production” Files

File 1: A Raw, Unedited File (good-production_01_raw-recording.wav)

This file has a few issues that need to be resolved before it can pass QA, the mouse clicks and excessive spacing at the start of the file for example, but nothing you hear can’t be resolved during the editing and mastering stages.

File 2: An Edited File (good-production_02_edited-recording.wav)

This next file contains the same performance, edited properly.


Notice the edits made between “Step 1” and “Step 2.” We trimmed the spacing (circled in purple) at the top of the file to half a second, and removed the mouse clicks and deep intake breaths (circled in yellow), replacing them with clean room tone.

Learning proper editing techniques can take some time, but I’ve found that the Alex the Audio Scientist blog post on editing and spacing is a helpful starting point. I even use the same QC sheet referenced in Alex’s post when I work on my own projects.

File 3: An Edited Master, Pre-Encoding (good-production_03_edited-mastered-recording.wav)

Ever wonder what a file that meets our Audio Submission Requirements, with peaks around -3dB and RMS levels between -18 and -23dB RMS, would look like in your DAW? This is it! Observe how consistent the peaks in this file are, then check where this file peaks on your meters. If your file is too dynamic or sounds a little muddy, you may need to utilize mastering tools like those detailed in Alex the Audio Scientist’s Mastering Audiobooks blog post

The “Avoid” Files

The “Avoid” files contain common problems you should steer clear of during production. Included here are:

  • A file that has been recorded at levels that are too low,
  • A file that’s been heavily gated,
  • A recording processed with heavy noise reduction, and
  • Files with Peak or RMS levels that do not meet our requirements.

You should not use these files to calibrate your system for recording. Rather, train your ears to notice these sounds as you work on your own files, and use these examples to understand the most common issues you may run into during production.

Try It Yourself

The sample pack also includes the script used during the recording of the samples. If you are testing out your levels before you begin a new project and want to compare your recordings to the “target” files in this pack, we recommend you use this script, which can be found on the last page of the file “ACX—Sample Guide.pdf.” Record your read of the script and compare your noise floor and peak level to the “Step 2” file. The closer you can get to matching the samples, the more confident you can be that you will pass QA inspection later on in the process.

Final Thoughts

It can be easy to get caught up in post-production, using too many plugins or tools when trying to meet specifications, or trying to fix poorly recorded audio that is beyond repair. At ACX, we believe the best time to address audio issues is before they make their way onto your recording. Training your ears to know when problems are occurring will be far more beneficial than having the latest noise removal or EQ plugins will ever be. The better you get at listening to yourself, the better your productions will sound to others.

Did you find the QA Team’s Reference Sample Pack helpful? Tell us in the comments below.