Audacity for Audiobooks: ACX Settings, Macro and Export

Audacity 3.7 or Audacity 4?

Audacity 4.0 rebuilt the interface on Qt, and its release notes say “most Audacity 3 workflows remain available, but some controls have moved or changed”.² For an audiobook, the differences that matter:

The menu paths below are Audacity 3’s, which most tutorials use. Audacity 4 keeps the effects in its Effect menu, but if something is missing, Audacity 3.7 is still offered on Audacity’s site as an older version.²

Recording settings

1. 1

   Choose the microphone and mono

   In the Audio Setup toolbar pick your microphone and Mono: a single voice needs one channel, and ACX wants every file in a book the same (all mono or all stereo).

2. 2

   Set the project to 44.1 kHz

   ACX requires 44.1 kHz files, so record at that rate rather than converting later.

3. 3

   Set the level

   Start Monitoring and read a paragraph: normal speech should sit between −18 and −12 dB on the meter, with occasional peaks near −6 dB and never in the red.

4. 4

   Measure the room first

   Record ten seconds of silence and check it with ACX Check, or measure the room with the noise floor meter: under −60 dB is ACX’s limit.

Audacity’s audiobook page adds two habits worth keeping: start from an unprocessed recording, and export each raw chapter as a 16-bit WAV backup before editing, “ideally not on the machine”.^1,9,14

Punch and Roll

Narrators fix mistakes as they go with Punch and Roll: stop at the mistake, click just before it, and press Shift+D (Transport > Recording > Punch and Roll Record). Audacity deletes everything after that point, plays five seconds of pre-roll, and records again from the splice with a 10 ms crossfade. Wear headphones, and set latency correction first so the splice lands in time.⁸ Audacity 4 rebuilt Punch and Roll for its new interface.² No install at all? The narration recorder does punch-and-roll in the browser.

Cleaning up: clicks, breaths, sibilance

Audacity’s audiobook page is blunt: its mastering suite does not address “harsh sibilance, gritty voice or wet mouth noises”.¹ What Audacity offers:

• Click Removal (Effect > Noise Removal and Repair) needs a selection of at least 4,096 samples; Repair fixes one click of up to 128 samples.¹⁰ Both were made for crackle as much as mouth noise, so listen after each pass.
• Breaths: select each one and lower it with Amplify (a negative amount), or replace it with room tone. Audacity has no automatic breath tool.
• De-essing: Audacity has no built-in de-esser (Audacity 4.0.1’s built-in effects include none),¹³ and Audacity’s plugin site lists none, so you need a third-party VST3 plugin.

Mastering for ACX

Audacity’s own process, from its Audiobook Mastering page. Select the whole chapter first.¹

1. 1

   Effect > EQ and Filters > Filter Curve EQ

   Presets & settings > Factory Presets > Low roll-off for speech > Apply. It removes rumble below the voice.

2. 2

   Effect > Volume and Compression > Loudness Normalization

   Normalize RMS to −20 dB (not the default perceived loudness), then Apply.

3. 3

   Effect > Volume and Compression > Limiter

   Hold every peak under −3.5 dB, half a decibel inside ACX’s −3 dB (settings below).

4. 4

   Analyze > ACX Check

   Peak no louder than −3 dB, RMS between −23 and −18 dB, noise floor −60 dB or quieter. If the noise is under about −65 dB and it sounds right, you may be done.

The settings stay where you left them, so later chapters are select, Filter Curve, Loudness Normalization, Limiter, ACX Check.¹ Loudness Normalization’s RMS option and Audacity’s −20 dB default are why that number appears everywhere.⁵

The macro (Audacity 3)

Audacity’s page offers the same chain as a macro: download Audiobook-Mastering-Macro.txt, import it in Tools > Macro Manager, then run Tools > Apply Macro > Audiobook-Mastering-Macro on a chapter.¹ Run ACX Check on the result. Audacity 4.0 has no Macro Manager.²

Installing ACX Check

ACX Check isn’t part of Audacity: it is a free Nyquist plugin by Steve Daulton on Audacity’s plugin site. It shows the peak, the RMS and the noise floor, measured from the quietest half-second of the selection, and warns when the sample rate isn’t 44.1 kHz or a file is longer than 120 minutes.⁶

1. Download ACX-Check.ny from plugins.audacityteam.org (Analyzers)
2. Tools > Nyquist Plugin Installer > Browse > ACX-Check.ny
3. Open > Apply > OK, then restart Audacity
4. Select a chapter > Analyze > ACX Check

Its own notes warn that a pass is “no guarantee of ACX acceptance”, and that a whine (USB interfaces often add one near 1 kHz) can be rejected even under −60 dB.⁶ Our ACX checker measures the same three numbers in the browser, for a whole book at once.

When the noise fails

Noise over −60 dB is the usual home-studio failure. Audacity’s suggestions, gentlest first:^1,11

1. 1

   Get a noise profile

   Select a few seconds of room tone only, open Effect > Noise Reduction and press Get Noise Profile.

2. 2

   Reduce gently

   Select the chapter and apply Noise Reduction at 6, 6, 6 (noise reduction dB, sensitivity, frequency smoothing). Not enough? Undo and try 9, 6, 6.

3. 3

   Stop before 12

   At 12 dB or more the voice can turn “wine-glassy or honky” and may not pass ACX’s listening check. Fix the room or the microphone instead.

4. 4

   Hum and whine

   A steady hum at one pitch responds to Effect > Notch Filter; USB whine responds badly to Noise Reduction.

Audacity’s page puts ACX’s human quality check plainly: it “does not like heavy processing”, and the audiobook should sound like “someone telling you a story over cups of tea”.¹

Exporting for ACX

File > Export Audio, one file per chapter:^12,14

Keep 1 to 5 seconds of room tone at the start and end of each file, and keep a WAV of every mastered chapter: MP3 is lossy, so re-export from the WAV if you need to fix something.¹⁴ The ACX requirements guide lists every rule, file names and credits included.

The no-install route

Every step above also exists here, in the browser, with nothing uploaded: the noise floor meter, the narration recorder with punch-and-roll, narration clean-up for clicks, breaths and sibilance, ACX mastering for RMS, peaks, noise and room tone (out as 192 kbps CBR MP3), and the ACX checker. Mix them with Audacity as you like: record and edit in Audacity, then clean up and master here.