Why did ACX reject my audio?

Most rejections come down to a handful of problems, and most can be fixed without re-recording. Find your reason below.

Technical failures (the automated check)

Noise floor too high

What it means: the quietest parts of your file (pauses, room tone) are louder than -60 dB. That's hiss, hum or room noise.

Fix: if it's close (say -57 dB), gentle noise reduction or a downward expander on the pauses will usually pass. If it's far off, the noise is coming from your room or your gain: record somewhere quieter, turn off fans and appliances, and set the mic gain a little higher so less gain is needed afterwards. Heavy noise reduction trades a noise failure for a "processed-sounding" one.

RMS too low or too high

What it means: the average loudness isn't between -23 and -18 dB.

Fix: apply gain to bring the average to about -20 dB, with a limiter so peaks stay under -3 dB. Normalizing peaks alone doesn't control RMS; you need loudness-based gain plus limiting.

Peaks above -3 dB

What it means: the loudest moment in the file is too hot.

Fix: lower the limiter ceiling to around -3.5 dB. MP3 encoding can push peaks up a few tenths of a dB, so a file limited to exactly -3.0 dB can fail after export. Always measure the final MP3.

Wrong format: VBR, bitrate or sample rate

What it means: the file isn't a constant-bit-rate MP3 at 192 kbps or higher and 44.1 kHz.

Fix: re-export with CBR (not VBR or ABR), 192 kbps, 44.1 kHz. Recording at 48 kHz is fine as long as the export converts to 44.1 kHz. Make every file in the book the same channel format: all mono or all stereo.

Missing or excessive room tone

What it means: the file starts or ends abruptly, uses digital silence, or has more than 5 seconds of room tone.

Fix: pad each file with 1 to 5 seconds of your real room tone at the start and end.

File too long, or chapters combined

Fix: one chapter per file, each under 120 minutes. Split long chapters with a secondary header. Opening and closing credits each go in their own file.

Quality failures (the listening review)

Inconsistent sound between chapters

Different rooms, mic positions or gain settings make chapters sound like they were recorded in different places. Keep notes on your setup and repeat it exactly. Process every chapter the same way.

Mouth noise, plosives and clicks

Clicks, lip smacks and popped "p" sounds are the most common reasons a technically perfect file is sent back. Hydrate, use a pop filter, speak slightly off-axis, and listen on headphones before upload. Small clicks can be removed one by one in an editor; a de-click plugin helps with many.

Background sounds and outtakes

Page turns, mouse clicks, chair creaks, a dog in the distance, a retake you forgot to remove. A punch-and-roll workflow, where you cut back to the last clean pause and pick up from there, keeps outtakes out of the file to begin with.

Over-processed audio

Strong noise reduction, compression or EQ can make a voice sound thin, watery or pumping. If you needed heavy processing to pass, the room is the real problem.

Before you resubmit

1. Measure every file: RMS, peak and noise floor, from the final MP3.
2. Listen to every chapter on headphones, start to finish.
3. Check the format of every file (CBR, 192 kbps, 44.1 kHz, same channel format).
4. Re-read the full list of ACX requirements and ACX's official page.