ACX Dang that noise floor

With the help of Audacity, I’ve been recording books for some time, and have 6 or 7 on Audible at present. THANK YOU for everything you do. This searchable Forum has been such a help over the years!

I ran into something with this latest book. I have already recorded the whole book, and a friend mastered it, and I submitted it, and was told that I needed to raise the RMS and diminish the noise floor in some chapters. I have been going through and getting things tidied up for re-submission. I did not know of the existence of ACX Check and what a help that is.

As I go through I’m finding that some of the chapters have a sound that doesn’t appear on others, something in the noise floor. Perhaps I will end up just re-recording those chapters, but I wanted to see if it is possible to save them. If nothing else I’d like to understand what I have here, and how to handle it.

I’m attaching a short clip from the raw WAV file

, and secondly a clip after I used Notch Filter, then Amplify, then Limiter

. Hard to believe, but this edited version of Chapter 6 passes the ACX check–this little clip doesn’t, but the whole chapter does. I can still hear the sound, though, and think they might turn it down anyway due to that noise.

Grateful for any instruction and help you can give me, even if I do end up having to re-record.

See [u]Audiobook Mastering[/u].

You’ll need to get the levels set before any noise reduction because boosting the audio will also boost the noise.

Since you’ve passed before (with the same setup and the same room studio?) some slight noise reduction will probably get you there.

Ch 6 Raw has a stupendous amount of noise back there. Are you in a room with loud air conditioning or other forced air system? That’s what it sounds like.

I can’t Noise Reduce it. By the time I get it to pass, Noise Reduction is starting to make your voice like talking in a wine glass. If I really lean on the correction, the voice volume starts to wander and throws the other readings off.

ACX Check looks for one good second of background silence in the whole chapter and measures that. The rest of the chapter could be complete trash as long as you have that one well-behaved second in there, it will seem to pass. That’s why they have Human Quality Control in addition to the automated testing. There is another common item, too. It has to be room tone or “real” background sound, not Audacity > Generate > Silence. They look for noise values that are too good.

Any idea what that wind noise could be? I guess it’s possible it’s microphone noise. But if it’s coming and going, that’s the signature of HVAC or Air Conditioning.

This is not good news. ACX usually wants the chapters to match. Patching up one chapter to not only pass, but match can be a challenge.


Thanks so much for your help. Sounds like I’ll have to do some re-recording.

It’s funny about some files being like this and some being fine. I recorded all my other books right at that same desk. There must have been something contributing this extra noise, off and on, that I didn’t notice at the time.

Do you happen to know–I think when I was first recording for ACX, I read somewhere that the allow you to re-submit a book only once. If they reject the second version, you can never submit that book again. Do you remember whether that’s the case? If so, I need to make it really perfect.

It look electrical: the noise above 16kHz is attenuated when the person is speaking,
& there is virtually no noise at 900Hz …

I read somewhere that the allow you to re-submit a book only once.

That’s a little severe, but it wouldn’t surprise me. Typically, they only complain about one thing whether your presentation has multiple problems or not. It’s not their job to troubleshoot your studio.

We should note the alternative to home recording is not stop reading. It’s read in an actual sound studio with a recording engineer. More than one poster is on the forum because they stopped using a successful sound studio and decided to read at home…and couldn’t.

I’ve been recording books for some time, and have 6 or 7 on Audible at present.

That makes you the unicorn. Usually somebody with that severe a problem just fails first time out. No casual home user ever passes ACX Noise. It’s severe. -60dB means background noise has to be 1000 times quieter than your voice.

You really can’t hear that noise in real time?

It look electrical: the noise above 16kHz is attenuated when the person is speaking,
& there is virtually no noise at 900Hz …

I noticed that odd sound signature. Noisy microphones or microphone interfaces tend to be “rain in the trees” sound without lumps and bumps in the tones. It’s also possible this is computer fan noise—a computer is warming up after a long time in use and deciding to cool itself. I have a machine which works like that. A half-hour into heavy use and I can hear a low-volume rushing whistle as the fans kick in.

In any event, because you are a unicorn, you know how to fix this—how to read successfully. Repeatedly read until you get a clean chapter. Do pay attention to the timing of the failures. Are they always the last chapter after long sessions?

It’s also good you can hear the failures. There have been posters with bad speakers or headphones who couldn’t hear the problem. Those people are in serious trouble.


We can continue to troubleshoot with you. The forum record is Ian who just wanted to record audiobooks from his apartment in Hollywood. 39 forum chapters and over a year.

I forget his name, but the one before that was a guitar performer who just wanted to record his Flamenco music. We replaced his microphone system.


Found it.

The second longest post in forum history is by Bruno in Portugal. He wanted to record Flamenco guitar on his computer. That was the whole job. 18 forum chapters over three and a half months.


No casual home user ever passes ACX Noise. It’s severe. -60dB means background noise has to be 1000 times quieter than your voice.

Ch 6 Raw background noise is 100 times quieter than your voice.


You guys are the greatest. Thanks for being there.

Sounds like there’s really no way to fix the problems in this chapter; I’ll need to re-record it.

The reason for the unicorn might be that I used to record in a home studio in Maryland, and now I’m recording in a home studio in Tennessee. It’s the same equipment, but a different room.

HOWEVER I think I recorded both Chs 5 (fine) and 6 (awful) while still in Maryland.

Today I’ll explore later chapters, and see whether the problem appears and disappears.

I bought my equipment in Dec 2010, following the advice of someone who’d seen a YouTube I posted and spotted a number of problems right away. I bought what he recommended:

Behringer C-1U Studio Condenser Microphone with USB Interface
(Dynamic would have been better, right?)

Behringer HPS5000 Studio Headphones

(and I’m currently using Audacity 2.3.3)

Thanks for helping me out. I’ll let you know later how chapters 8, 9, 10 etc sound.

Incidentally this is my book “First Fruits”,
It’s a one-reading-a-day book, for 40 days. Originally I had 10 chapters, 4 “days” per chapter. Then I realized that would be hard for a listener to navigate if trying to find a particular day (esp while driving). So after ACX rejected it (voice too quiet, noise floor too noisy), I divided it into 40 separate, short chapters.

Behringer C-1U Studio Condenser Microphone with USB Interface

I have a plain C-1.

But I have a USB interface (on the left) which comes built-in with yours.

(Dynamic would have been better, right?)

Dynamic microphones can have their own problems. I’d be more in favor of finding out where your noise is coming from, particularly since your current setup has been successful. I don’t think you can buy your way out of this problem.


Quick update–I’m up to Ch 20, and so far only Chs 6 & 7 have the noisy Noise Floor (say that three times fast). The others are OK.
Mysteries of the Audio Universe.

so far only Chs 6 & 7 have the noisy Noise Floor so far only Chs 6 & 7 have the noisy Noise Floor so far only Chs 6 & 7 have the noisy Noise Floor so far only Chs 6 & 7 have the noisy Noise Floor

And the only real shortcoming to doing is this way, assuming ACX accepts your work, is Voice for Hire. You can’t just tell a client you’re going to present their work. It will always be: “There’s an 80% chance I’ll present your work because sometimes my system does something funny.”

Being obsessive, that would make me insane.


I never was able to figure out a way to get into the Voice For Hire racket. So I only have to please myself; I record only my own books.

But because people always told me I have a nice voice, I recorded books for the blind for many years. Maryland (and I was told, every state) has a closed-circuit radio station where volunteers read the newspaper, TV listings, novels, magazines, all kinds of things. Reading novels was fun.

Well, I uploaded all the files to ACX today, and we’ll see what happens. I had to record new Chs 6 & 7, and they pass the ACX Check (like all the other chapters), but they do sound somewhat different since they were recorded in my new house. Hopefully it’s close enough to pass. Thanks for your help. I will be back, if they give it thumbs down.

Hopefully it’s close enough to pass.

I don’t think anybody at ACX is going to sit and listen to every word of every submission (in my opinion). It’s a much better business model to inspect new users in great detail and back away to casual spot checking as the ability and fame of the reader improves. It’s possible they won’t catch it, but plan what you would do if they do.

Again in my opinion, an inspector would spot check each chapter which would show the quality shift immediately.


Hi there. I opened this thread in November while trying to prepare files to re-submit to ACX. I’ve passed ACX approval quickly in the past and have 7 audiobooks for sale at present.

With this new book, “First Fruits,” I recorded most of it at my home desk in MD, and the rest of it after moving to TN–a new location, but same equipment.

I submitted it and received a Review that the noise floor was too high, and my voice was too low / soft. With your help I worked everything over (using Amplify, Notch Filter, and Limiter if necessary) and tested each file on the ACX Check; they all passed.

So I submitted these new files on Dec 3, and yesterday I received a Review stating:

<<Issue: All files contain excessive background/ambient noise and do not meet our noise floor requirement. Please revise all files.>>

I guess they think voice volume is OK, and dramatics etc are all right. I’m relieved that they didn’t notice a distinction between the MD and TN recordings.

(They do also say some files are not quiet enough at the beginning and end. Wish they’d said which ones! I’ll take a quiet patch and stick it on the beginning and end of every file.)

I am attaching a sample from a chapter I submitted to ACX. This was recorded in my new home office. ACX did not differentiate between the new recordings and the older ones from my last home.

I might just have to re-record the whole thing. 9 hours! Bummer!

They do also say some files are not quiet enough at the beginning and end.

Can you post the exact response?

You may be the second reader that moved houses in the middle of a book and ran into troubles. Unless you moved from a soundproof studio to another soundproof studio, the recordings are always going to pick up some of the room flavor. ACX hates distractions and having the chapters change background is a distraction.

It would be really good to read their exact response. Having your voice change volume through a recording can indicate Windows settings problems.

Are you following the Audiobook Mastering suite of tools? Does that ring a bell? You didn’t say that anywhere in the post and you have problems and errors the suite was designed to fix.

Can you record a test? I know you’re not a New User, but you did move houses and ACX started rejecting your work. Something happened.

Read down the blue links. They’re very short.


I know I moved from Maryland to California and my voice recordings are very different now.

… ??

Mostly because the California place has a sound studio. Hard to beat that.


It’s possible squeeze down the noise using noise-reduction & an expander

Rather than using Audcaity’s amplify, have you tried turning-up the mic-gain/boost in Window’s recording devices ?
Doing that maybe could also improve the signal-to-noise ratio, (worth a try).

That mic currently costs less than $40 : it’s not really a professional spec item.
A stand-alone recording device will have lower-noise, (they can be hired by the day).