ACX Check Issues

Audacity 2.4.2
Windows 10 x64
I am trying to pass ACX Check.
I have a Focusrite Scarlett Solo 3rd Generation connected via USB and Rode nt1-a microphone connected via XLR into my interface.
I have set everything as described through the Audiobook Mastering Tutorial in the Manual.
When I record a chapter I run RMS Normalize then ACX Check. This has always failed ACX standards.
My RMS is good, but Peaks are too high as is the Noise Floor. When I try to adjust my Peak Levels through Normalize and Noise Floor through Noise Reduction effects this throws off RMS. Looking for suggestions. Thank you.

Follow the [u]Recommended Audiobook Mastering Process[/u] in-order and you’ll pass RMS & peak level EVERY TIME!

The Low Roll-Off for Speech removes low-frequency nose.

RMS Normalize sets the RMS level (and the overall “loudness”). RMS Normalize usually boosts the volume so it boosts the noise floor and the peaks and it usually pushes the peaks out-of-spec.

Limiting pushes-down the peaks with very-little effect on the RMS level.

Then, you may need to work on the noise. (Most home studios are not soundproof and home recording equipment is usually noisier than pro equipment.)

That’s weird. The blue link doesn’t go anywhere. This link should do it.

You can post a very short sound test on the forum and we can do an evaluation.

Read down the blue links in that post. They’re very short.


I fixed it.

Thanks guys!

Attached is a raw, unedited version of the sample for evaluation.

I did ACX Check post recording of the raw sample. Only thing was my RMS was -50.

After RMS Normalize I’m at -20db, but Peaks are -0.1; Noise Floor -45.8.

In essence RMS Normalize amplifies unwanted background noise? What settings are appropriate with Noise Reduction effect?

Interesting. It looks like after RMS Normalize, with setting Peak Amplitude to -3.1, with Noise Reduction settings at 6, 6, 3 I have passed ACX Check with -3.1; -20.8; and -62.4. This does seem like it is cutting things close.

Thank you all for helping this newbie with his new venture.

I didn’t listen, but if it “sounds OK” you should be good-to-go.

Only thing was my RMS was -50.

You should be able to record “louder”. You may need to turn-up the gain on your interface, speak louder, or get closer to the mic, etc. And, make sure you are talking into the front side of your directional side-address microphone.

In essence RMS Normalize amplifies unwanted background noise?

Yes. It’s a linear volume adjustment. The RMS, peak, and noise, are all adjusted up (or down) by the same dB amount. (It’s almost an upward adjustment from the raw recording unless you’ve clipped/distorted the peaks.)

You’re going to need to come up with more loud.

Note how tall the blue waves are on your sound file and how tall they are after I mastered it (starting at 2). This is after.

Screen Shot 2020-07-21 at 12.03.15 PM.png
Now look at yours.

This is the relationship between the dB numbers.

For a raw reading, occasional loud peaks may make it up to 50% on the blue waves. It’s never supposed to reach 100%.

Also announce so the green, bouncing sound meter just starts to turn yellow here and there. The meter is never supposed to turn red.

What’s the microphone? Sometimes there’s tricks to using microphones. You don’t always just announce into the end opposite the cable.

Home microphones are almost always of modest volume. If you announce softly, you can create a show that almost vanishes it’s so quiet.

Nobody announces directly into ACX, but you do have to get closer.

Continted? Not Contented? Is that a regional swing? Is it your book?


I downloaded RMS Normalize function as mentioned in “Audiobook Mastering” Tutorial. Should I use this in lieu of the Loudness Normalization effect? By following the steps outlined and my lights turned off I am passing ACX Check.

I want to get it right, but ore importantly I want to understand every aspect of the Effects- what they mean and what they do. How can I learn this?

I am using a Rode nta-1 mic

The ACX spec is RMS.

You can use Loudness Normalization as long as you choose the RMS option.

It appears to be working well. Attached are a new, mastered clip and the ACX Check results.
ACX Eval.png

I want to get it right, but ore importantly I want to understand every aspect of the Effects- what they mean and what they do. How can I learn this?

The low frequency roll-off cuts the low frequencies (bass) below the normal voice range. There is usually (relatively) lots of low frequency noise and this filtering removes any low-frequency noise without affecting the voice. If you use that effect on music you’ll kill the bass but it doesn’t harm voice. (Our ears are not as sensitive to low frequencies so you may not hear the low-frequency noise, but ACX check will measure it.)

Normalization is simply a volume adjustment to a target-level. [u]RMS[/u] is a kind-of average which correlates reasonably-well with “loudness”. (The actual average is zero because the waveform is positive half the time and negative half the time.)

Limiting “pushes down” the peaks without [u]clipping[/u] (without distorting) and without affecting the rest of the waveform.* Normally, limiting has very little effect on the RMS levels. It’s typically used to so you can get the volume louder without clipping. (Audacity itself won’t clip, but many file formats won’t go over 0dB and your digital-to-analog converter won’t’ go over 0dB.) In general you can go all the way to 0dB on the peaks but ACX is more strict and they want the peaks below -3dB.

[u]Noise Reduction[/u] is more complicated than the other effects. It takes a Noise Profile (AKA “Noise fingerprint”) and it tries to remove the noise without excessively damaging/removing the other sounds .


  • If you over-do limiting it you can end-up with squared-off waves similar to clipping and it can sound like clipping.

Thank you all for your help. I look forward to the day when I can teach someone else about all of this. For now I will take my time and keep working at it.

It seems that I am getting the hang of the basic ACX design. Time to get the thing going.

I am very grateful for everyone’s help on this. It was rapid and very effective.

Thank you, again.

Time to get the thing going.

The Audacity tools and techniques are based on our reading of the ACX specifications and publications. They didn’t write the tools. When you submit something, it not only should pass ACX Check, it also must pass the ACX Robot which measures many of the same things, but also Human Quality Control which judges things like theatrical presentation and your unfortunate tendency to spit on the microphone when you talk.

I’m only partly joking about that.

In order to not waste tons of time, ACX will let you submit a short “audition,” first.

I’m going to make this into a pretty web page any minute now.

ACX-Auditions.txt (1.5 KB)