RMS, Amplify, Noise floor

Hi all,

I’m on a Macbook Pro, Sonoma v14, Audacity v3.3.3 and I’m having a difficult time passing the ACX check. When I adjust the amplify setting to -3 (among other settings between -3 and -5) it passes. When I try to adjust the RMS to be in the acceptable range, it goes haywire and I can’t get it below 29. I’ve tried noise reduction, normalization, limiter, etc. and I can’t get the RMS in range. My current project passes with a peak level of -3, noise floor of -88.24, but the RMS is -29.10 on a consistent basis. What can I do to straighten it out? Any advice would be greatly appreciated.


ACX Check is one of two handy-dandy tools for audiobook reading. Audiobook Mastering Macro is the other one.

Mastering guarantees Peak and RMS (loudness). If you read in a quiet, echo-free room, you may be good to go.

There are still theatrical and business considerations. Mouth noises and that selling your book on Amazon, thing.



Linear volume changes (Amplify, Normalize, Loudness Normalization, etc.) change everything by the same dB amount. i.e. If you increase the RMS by 3dB, the peak and noise level also increase by 3db.

Typically you can never hit all 3 numbers with linear adjustments.

The limiter is not linear. It pushes-down the peaks and has very little effect on RMS or the noise level. When you set the RMS correctly the peaks are usually too high so the limiter is applied after setting the RMS level.

Similarly, you need to check (and optionally fix) the noise floor after setting RMS.

Exactly what I need to know, thanks!

There is a relatively new service brought back to life after being silent for the pandemic. Sample Review. They will evaluate a short, posted sample.


They used to do this and that’s how I found out my mouth wasn’t cut out for reading books. Then they stopped, my guess is when half the staff called in sick.


A note: Audiobook Mastering includes all the settings needed to pass ACX including some of the “fudge” values you don’t normally think about. It also includes Low Rolloff For Speech rumble filter similar to the one used for broadcast and movie production.

Can I buy your book on Amazon right now? That’s one of the odd requirements for ACX publishing.


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