Chapter fails "ACX check."


I am a publisher and have been involved in many ACX audiobooks. This book is personal as it was written by me. The narrator blew my mind with his audition and I accepted on the spot. However this is his first acceptance so a newbie.

We have all 22 chaps done and after him watching a Webiair he heard about ACX Check and RMS Normalise. he ran both and the chapter failed. (I have attached chap on Dropbox below.

Can you guys advise what we should do?

It passes using the Audacity ACX Check tool

nominal ACX pass.png
but it has conspicuous noise-reduction artifacts …

If ACX are rejecting it that could be the reason.

Noise-reduction damage is not reversible.
Hopefully you have a version before noise-reduction has been applied.

Home reading audiobooks is not for the easily frightened.

I hope to goodness you have WAV or Audacity Projects of each raw chapter of the read. We can’t take effects, corrections or filters out of a production. Once you master, that’s the end of the world.

There is a published ACX Mastering process.

Please note it starts with a raw, uncorrected reading and if you read in a quiet, echo free room, that’s all you need.

Noise Gate and stiff Noise Reduction are not recommended. If you believe ACX, they are forbidden. They take a hard line on this stuff.

So, do you or your presenter have Audacity Projects or WAVes of the original, raw, unprocessed reading?


him watching a Webiair he heard about ACX Check and RMS Normalise

Which webinar?


ACX Check only tests for technical conformance. It can’t tell theatrical quality. Somebody with a damaged voice or uncomfortable reading style can sail right by ACX Check and still produce an unlistenable product. ACX uses technical conformance as a first step and then subjects the work to Human Quality Control. That’s where you go to die if you have clinical asthma, for example.

You can fake out ACX Check, too. It needs at least 3/4 second of clean room tone (background sound) to measure ACX Noise. If it can’t find that, it will measure whatever it can find and may fail a perfectly pleasant performance.

There is a trick to this. It’s possible to get ACX Check readings too good. Nobody can read a performance with noise in the -80dB range. It’s almost impossible. So anybody with readings like that must have been messing with the sound and hope nobody notices.


Thanks guys, my narrator didn’t save the original files so only has mp3. He is new to this. Someone has suggested a limiter?

How and what is the .flac file above and how do I open it?

FLAC files are the same high quality audio files as WAV files, but use “lossless compression” to reduce the file size by about 40% without affecting audio quality.

Flac files can be imported into Audacity and played, or if you install a good audio player (such as Foobar2000) you can play them, or if you install the “DirectShow filters” ( you can play them in Windows Media Player.

Someone has suggested a limiter?

We suggest reading it again.

The voice timber and quality is damaged from either excessive noise reduction or MP3 compression artifacts…or both. MP3 works by throwing away sound it doesn’t think you want any more. There is no good quality voice left to rescue.

You are well into the middle of the production process with the presenter and we never established whether anything he does is acceptable. We know he has already made several very serious production errors even past the voice damage.

Please perform and post a 20 second mono sound clip of raw voice performance.